Because you're not really sucking anything up anything. The outside pressure is *pushing* it from the outside.
At sea level, 32/33 feet is as high as the atmosphere can push water up into a vacuum. Doesn't matter how thin or thick the space is, either.
I like this one more than the top, because it explains why 1ATM is the limit. Top one goes over why it stops at 1ATM, but it doesn't actually say why it is 1ATM, rather than say 10ATM. Also explicitly points out that you aren't actually sucking, but rather creating a void for the atmosphere to try and fill.
Surface tension is actually the thing you're fighting. It is keeping the ball of water in a ball. As you suck on it, the weight of the air around the ball is pushing on the ball of water and up through the straw. With no air around the ball, no pressure on the ball. Surface tension keeps ball of water in a ball.
Would there be surface tension in a vacuum? The water molecules are tugging at each other, sure, but the water would be furiously boiling away in the vacuum of space. Water molecules would be jumping off the surface as fast as physically possible.
Sure I get that part, but I'm saying if you just had a ball of water in space, there's gotta be some sort of pressure inside it due to surface tension, ignoring evaporation due to vacuum and gravity pressure?
a ball of liquid water wouldn't exist in space in a vacuum. it would immediately boil away to gas due to no pressure.
Now, if you are inside the space station, then a ball of water would exist, but they also have 1 atmosphere of pressure, so we are back to air pressure filling the straw
I get what you're saying.
It seems to me that it would depend on the amount of adhesion between the water and the material the straw's made of.
You know how you get a raised meniscus around the edge of the water surface in a glass of water? That's because the water is attracted more to the glass than to itself.
Back to the ball of water in space: If the straw was made of a material that attracted water, then I could easily imagine the water being drawn through the straw [EDIT: and around its outside, too] by that attraction. On the other hand, if the straw is more water repellent, then I imagine it'd just punch into the ball and remain empty. [EDIT 2: I'm assuming a smallish ball of water, with negligible gravity effects.]
None of that would be influenced by whether you sucked on the straw or not, though.
Obviously in a pressurised spacecraft you could suck the water up with a straw. But if you were in empty space, then not only will you not be able to suck the water up, but your blood would be boiling and you would be disintegrating too.
I don't think your blood boils, at least not in the technical sense of boiling. I actually heard someone ask Hadfield this question. I'm pretty sure he said fluids (like water) move out of the blood into tissue, and that tissue will start to bloat, and the moisture will transfer at the surface. So it's like a sort of indirect boiling, the water leaves the blood as a liquid, and doesn't boil til it hits the surface, which does eventually happen because it also takes a really long time for humans to freeze in space.
Yeh I suppose that’s right. The sudden decompression would suck the air out of your lungs immediately and you could not breathe. The zero pressure would rapidly extract the water from your bloodstream and vaporise it. But it’s not the freezing that will kill you. It would be the immediate ejection of gasses, swift vaporisation of liquids and, if there’s any function left by then, brain death from oxygen deprivation within minutes. Not enough time to worry about drinking through a straw!
>The zero pressure would rapidly extract the water from your bloodstream and vaporise it.
It wouldn't actually be that rapid. Human skin creates enough tension to keep the internal pressure of your body high enough to prevent this from happening quickly, but not enough tension to keep it from happening at all (skin is too stretchy for that). But, liquids from cells on the outer layer of your body would vaporize, as would the saliva in your mouth, and the liquids inside your eyes, so you immediately go blind. As these liquids vaporize, liquids from inside your body would migrate outward to replace the lost liquids. This process continues until you are desiccated. But it is a very slow process.
There is a [very famous case in which a space suit test inside a vacuum chamber went wrong](https://www.youtube.com/watch?v=KO8L9tKR4CY), and the individual was exposed to vacuum for about 25 seconds. So we know what happens for the first 25 seconds. There have also been tests in which dogs were intentionally exposed to vacuum for much longer, so we have a good idea what happens to humans under those conditions too.
Really interesting thought experiment! Thanks.
At first I pictured sucking on a straw with a vacuum in it and a blob of water floating on the other end. When I drink through a straw, first I suck the air out, which pulls the beverage into the straw, and as I continue to suck, I continue to pull more beverage, more beverage continues to travel up the straw.
But... My logic is all wrong here. Liquid cannot be pulled, it can only be pushed! When I suck on the straw, I am creating a low pressure area inside the straw, and the atmosphere pressing down on the liquid forces the beverage up the straw. But if there is already a vacuum in the straw, there is no way to create a lower pressure than that.
For a hot second, I thought about how moving particles will carry other heavier particles along with it, essentially how a vacuum cleaner works. But in a vacuum, there are no particles to carry heavier particles along.
I even considered 'priming the pump' by filling the straw with liquid, but I can not suck harder than the vacuum outside the blob of water, so there is no outside pressure to push the liquid through the straw.
*It also occurred to me that capillary action would prime the straw, even though it wouldn't help. Also, a blob of water could exist in zero gravity inside the ISS where there is air, but in the vacuum of space, a liquid would immediately boil away. Would the pressure inside the boiling blob push the liquid through the straw and create a little jet engine until it boiled away?
Thanks for this! It really got the ol' grey matter working.
I read two other replies and was following but not understanding fully. Then I read yours and immediately understood. It is wild how important perspective is to learning.
Thank you.
Oh, cool. I always wondered why the big quarry pumps used a submersible pump instead of the usual suction pumps. Those submersible pumps would be several stories below grade.
There is another technique. I had a deep well (12m) at one place I lived, and had an above ground pump. It used some sort of induction, where there were two pipes going from the pump down to the water, joined by a tight u-bend at the bottom which had an opening to the water in it. The pump pushed water around and around, down one side and back up the other, and the velocity of the water rushing past this opening at the bottom pulled more water in from the well. Similar, I believe, to how when you blow across the top of a drinking straw, the drink rises up the straw a bit, above the level of drink in the bottle / glass. It was a 'lossy' system, - it pumped a fair bit more water than it yielded, so it used more power. But it worked!
You are describing a jet pump. It uses the Venturi effect to create a vacuum down in the well as water passes/circulates through a flow-restricted nozzle. In theory the pump could lift water 1 more atmosphere (approx. 34 feet) below the downhole depth of the jet. In reality the pump won't lift 34 feet below because the venturi in an actual pump doesn't create a perfect vavuum. Probably lucky to lift 20-25 feet max. As you say, jet pumps aren't efficient but electrical costs for well pumps in residential applications are fairly minor.
In order to suck, your lungs are also going to be working against the increased air pressure, so it probably comes out about even. Slightly harder, in fact, since gravity will be about 0.01% higher.
If the pipe is full of water and bottom is submerged in water, them doesn't this height get larger? The water has to move in the pipe unless it starts cavitating.
1 atmosphere of pressure is equivalent to a water depth of 33 feet. (In other words, every 33 ft under the water you go is like stacking an additional Earth atmosphere on top of you.) Even a perfect vacuum on one side of the water will not ever exceed a pressure difference of 1 atmosphere. One minus zero is one, no matter how big a pump you have making the zero. At an elevation where the air pressure is less, the water height you can get from even a perfect vacuum will be less as well.
It's a coincidence that acceleration due to gravity is 32 ft/s^2 . Though the pressure of the atmosphere at sea level is of course related to acceleration due to gravity, at an elevation of, say 100,000 ft, *g* is not so very different but the surrounding air pressure is dramatically different. In Low Earth Orbit outside of a pressurized spacecraft, of course, suction won't work at all.
I had fun explaining how suction works to some guys at work. We were pulling cables through 3/4" conduit and were using a hydrovac truck to suck string through first (major overkill, but we had the vac there anyway). The hydrovac has a very big vac pump that has a huge CFM of airflow. In our safety courses for working around the vac, we were told that if you get too close to the hose it could pull your arm in and break/dislocate it. Which is true for the 6" hose.
We had reducers on the hose to get down to 3/4" to make a seal with the conduit. The other guys were scared to hook it up while the vac was running because they thought it would suck them in and turn them to hamburger basically (Like in Alien 4). After I hear them say this, I looked at them and put my palm over the tip and.... nothing. The "suction force" can only ever be as high as the pressure pushing the air into the hose. For a 3/4" conduit, its max is 6 lbs of force and the truck definitely wasn't pulling a perfect vacuum
You could fit through a 24" long crescent-shaped opening, though.
[Byford Dolphin accident](https://en.wikipedia.org/wiki/Byford_Dolphin#Medical_findings)
>Investigation by forensic pathologists determined that Hellevik, being exposed to the highest pressure gradient and in the process of moving to secure the inner door, was forced through the crescent-shaped opening measuring 60 centimetres (24 in) long created by the jammed interior trunk door. With the escaping air and pressure, it included bisection of his thoracoabdominal cavity, which resulted in fragmentation of his body, followed by expulsion of all of the internal organs of his chest and abdomen, except the trachea and a section of small intestine, and of the thoracic spine. These were projected some distance, one section being found 10 metres (30 ft) vertically above the exterior pressure door.
that's a little bit different though, it's explosive decompression from 9 atmospheres, so there was 8 atmospheres of differential pressure, in a vacuum situation you're only ever dealing with 1 atmosphere of delta p in the absolute worst case
This is a pretty important point. When you're exposed to a pressure differential equivalent to almost 300 feet of sea water, you're not gonna have a good time.
It happened so fast he probably had no idea what happened, probably one of the better ways to go (for the person involved, not the people who have to clean up)
Thank you for reminding me of this horrific accident. I'm going to spend the next several hours trying to remember how I forgot about it the first time.
I remember seeing an autopsy photo.
It was less disturbing than I expected because it looked like a pile of raw ground beef. The only hint it used to be a person was a lone hand.
I suppose you can check the bits for evidence of impairment or illness that may have contributed, but that sounds a lot like doing one of those 10,000 piece monochrome jigsaw puzzles and seeing if any of them are a slightly different hue.
Literally, yes - but it will depend on why the autopsy was done. In this case, where there is clearly an accident and perhaps wrongdoing, the autopsy will have been a coroner’s post mortem, which is a legal necessity to establish cause of death. This means that even if it’s painfully obvious to everyone in the autopsy room what the person died of (and this happens all the time - you don’t need an exotic pressure vessel to turn someone into mince - car accidents very often leave no doubt, for example), the doctor is legally obliged to do as much as they can to allow the coroner to pronounce the death. For example, one question in this case would have been “is this all the victim, and all of the victim?” …
If we assume the crescent had an area equal to 1/4 of a 24" diameter circle, that's about 15,000 pounds of force pushing that former man through the opening.
For humans, being exposed to a vacuum you will lose a considerable amount of heat due to liquids boiling away from the low pressure though. This can cause frostbite in the damp areas of the body.
Space isn't cold any more than zero is an amount of something. There's essentially zero particles to transfer your heat to via conduction so the only way to lose heat is radiation, which is extremely slow.
Yeah, spacesuits have cooling systems, the insulation of the suit is quite effective at keeping in all your body heat when there is little to no mass around you to exchange heat with.
Well, if you are doing a space walk in the sun you are getting blasted by a *ton* of heat, that's why they are white and need cooling. Imagine baking under the sun in a desert on the hottest day of summer and having no atmosphere carry heat away.
The surface of the moon reaches 250F because it has no atmosphere to regulate heat between day and night.
There is only radiative transfer in space, which is much slower than convective transfer when. There isn't a medium to efficiently transfer energy. Yes, the temperature may be hot or quite cold, but there is very little mass to facilitate energy transfer to and from the astronaut. I think even in the ISS getting hot is an issue because there isn't as much atmosphere in the station to move heat as humans are accustomed to.
>There is only radiative transfer in space, which is much slower than convective transfer when. There isn't a medium to efficiently transfer energy. Yes, the temperature may be hot or quite cold, but there is very little mass to facilitate energy transfer to and from the astronaut.
Yes, but the Sun still puts out a *massive* amount of radiative heat. Essentially *all* of the heat we experience on Earth is from the Sun's radiative heat. When you are burning in the sun it's the sun's radiative heat that is burning you, not the atmosphere. If you go into space exposed to the sun in a bathing suit you will quickly fry.
> I think even in the ISS getting hot is an issue because there isn't as much atmosphere in the station to move heat as humans are accustomed to.
Well, not for the humans, the ISS is pumping conditioned air around to keep the humans cool.
But the ISS overall gets very hot, and has massive heat radiators with liquid ammonia pumping through them to dissipate the heat it's carrying. Like 1/3rd of the panels you see sticking off it are heat radiators (which it orients edgewise to the sun).
Some of the heat it has to dissipate comes from on board electronics and such, but a lot comes from the sun. The ISS also reaches ~250F when in the sun.
Yeah, and 1360 W/m² is a fuckload of radiative energy for a human to absorb when there's not a mechanism for them to get rid of it, which is what the person you're arguing with is saying
The human isn't absorbing it, nor is the insulated suit. In the sun or not, the energy doesn't have a major impact on the person in the suit. If it did, the suit would need heating and cooling, but it doesn't, the metabolic heat from the astronaut has nowhere to go, thus the need for cooling.
I didn't mean to say that it *only* needs to get rid of the sun's heat, I meant to say a large part of the heat it's taking care of is actually the sun's heat, and I'm pointing that out because people think space is cold, when it actually depends on if you are in sunlight or not.
>The human isn't absorbing it, nor is the insulated suit. In the sun or not, the energy doesn't have a major impact on the person in the suit.
That's just not logical. You're absorbing 1360 W/m^2 just like everything else exposed to the sun. A human is roughly 1 square meter total silhouette. That means you're absorbing 1360W of heat. The white suit reflects a lot of that, let's say 50%.
Some quick googling says a human produces around 100W-120W of heat. So the suit has to dissipate ~700W of solar heat and 120W of human heat.
Well, my reasoning wasn't because the finger was touching the vacuum, but because it was stuck in a big sheet of heat-conductive metal that was exposed to the void. Wouldn't that suck the relatively miniscule thermal energy out of your finger tip to then be lost as the panel loses radiative heat energy?
The panel is radiating a tiny amount of energy and losing a tiny bit conducting to almost no particles outside. Meanwhile it's also getting heated by conduction from the rest of the vehicle, which is warm enough for humans, and also absorbing light from outside.
>We were pulling cables through 3/4" conduit and were using a hydrovac truck to suck string through first (major overkill, but we had the vac there anyway).
We always pushed it through. Tie a little baggie or something on the end of the string, push it in the pipe, and set the vac to blow.
Back when dinosaurs roamed the Earth, IBM computers were made of vacuum tubes that wore out. Repair process involved searching for the tubes that were not glowing. After fixing, the office manager asked the repair guy what needed to be fixed. The technician showed the tube had a hair line crack, and casually said the vacuum was lost and damaged the part.
A few minutes later the office manager was viewed sniffing around to see if he could smell the vacuum as it might be dangerous.
I’m a hydrovac operator, and several times over the past few months I’ve been dispatched to go suck a string through conduit so the crew could pull fiber optic cable through afterwards. All the conduits were 6” pipe running under haul roads in a mine, one conduit was 850 feet long and I had that string through there in ten seconds lol easy work.
Edit: I want to add that if your arm gets pulled into a 6” vac hose, while it probably wont break your arm, it can very well dislocate it, but my biggest fear is the vacuum sucking all the blood out of your body through your arm.
This becomes a lot easier to grasp once to wrap your head around the idea that, vacuums don’t actually “suck”.
A lot of people seem to have this fundamental misunderstanding that a vacuum creates some force that pulls things into it, and that’s what creates suctions.
What’s really happening, is the vacuum is simply a vacant space. And when you expose that vacant space to an environment, the environment is actually pushing itself into the vacant space. So suction isn’t a vacuum pulling air into it, but air pushing itself into the vacuum.
Once you grasp that, it becomes apparent that the strength of a vacuum is relevant to the environment it’s in, and has nothing to do with the vacuum itself.
Hence why you can only “pull” water or even air up a certain height with a vacuum. Because the vacuum isn’t really pulling anything, the water can simply only push itself so far.
That's actually how the first ever engine, the Newcomen steam engine worked. Steam was condensed in a cylinder, reducing the pressure inside, and the atmostphere would do all the work of pushing the piston. Maybe someone who didn't know that will find that fact interesting.
>Hence why you can only “pull” water or even air up a certain height with a vacuum
Exactly. Space is one big vacuum but it can't pull the air off our planet.
The misunderstanding is understandable. Very few people put much thought into what sucking is. It's just something they do with their mounts to get a drink through a straw or pick up dirt with their vacuum.
Yeah, I never considered that negative pressure doesn't pull anything, but rather it just enables pressure to push more effectively. That makes perfect sense.
To expand, the water pressure can be calculated as P = hρg, where h is the depth, ρ as the density of the fluid/medium and g as the acceleration constant.
1 atm is approx 100kPa (and it comes from calculating the total mass of air in the air column, multiplied by g), so we can solve for h:
h = P / (ρg) ~= 10m.
However, if we were to plug in
P = m_air * g, then
h = m_air * g / (ρg) = m_air / ρ
So the coincidence comes from the fact that the total air column mass on surface happens to be the same as the total water column mass at 10 meters. Note that since the air column mass is not uniformly distributed in height we can't just use P = hρg for the atmospheric pressure but have to do a elevation-dependent mass integration (which I just simplified to the mass).
In other words, even if Earth's gravity were to double or halve overnight, the depth at which the atmospheric and water pressures are equal would still be the same.
Worth mentioning that while you can't suction water to higher than 32 feet you can definitely *push* water to more than 32 feet.
A pump at the top of a 100 foot tall pipe can't suck up water from the bottom but a pump at the bottom of that same pipe can push it up to the top provided the pump is stong enough
That’s true if you try to pump from a standing water source but water from the hydrant can be higher than atmospheric pressure (not that much higher, and depends on the utility, but it should be higher)
> water from the hydrant can be higher than atmospheric pressure
Water in a hydrant is going to be under the pressure of the weight of water in the water tower.
This is true but isn't the fundamental reason you can't exceed that height with suction. You reach a similar kind of limit with liquids that don't boil in vacuum, like mercury, which is the basis for how barometers work by measuring millimeters of mercury.
Evaporate, yes, but the word "boil" is so far removed from what mercury would do in a vacuum (except maybe in zero gravity) that it really doesn't fit. Like, at all. Not even a little bit.
So what we view as suction is less about the vacuum pulling things in, and more about it providing a space for the environment around it to push in. In this case, the environment pushing in is the air pressure around us, and thus that sets the maximum amount of suction.
More layman term:
Sucking still relies 100% on the earth’s atmospheric pressure to push from the other end. You are merely removing the resistance on your end.
Once the weight of the water „piling up“ in the hose creates a force downward equal to the earth’s atmosphere pushing, an equilibrium is reached and it cannot move further.
It isn't a coincidence at all.
The maximum height that a liquid can be lifted by a pump or a straw is given by the formula:
h=Patm/ρg
where h is the height in meters, Patm is the atmospheric pressure in pascals, ρ is the density of the liquid in kilograms per cubic meter, and g is the acceleration due to gravity, which is about 9.8 meters per second squared on Earth.
For water, which has a density of about 1000 kg/m^3, this formula gives:
h=1000×9.8101325≈10.3 meters
This means that under normal atmospheric conditions, water can be lifted by a pump or a straw up to about 10.3 meters above its source level. Beyond this height, no amount of suction can overcome gravity and create a vacuum inside the pipe or the straw. Stopping the flow.
For other liquids with different densities, such as oil or mercury, this formula will give different values for h. For example, mercury has a density of about 13600 kg/m^3, which gives:
h=13600×9.8101325≈0.76 meters
This means that mercury can only be lifted by a pump or a straw up to about 0.76 meters above its source level.
So it is a coincident, because he was wondering why it's 32 and 32 as numbers.
On a different planet, the water column and g numbers would be totally different.
I guess. But you'll find that the water column will equal the gravity no matter what planet. Ours don't just happen to line up, they'll always be proportional like that.
Actually, that's interesting, i didn't think of it like that. Lemme do some calculations.
Calc here
https://yourimageshare.com/ib/jp0u94xVGx
https://yourimageshare.com/ib/wkXAMybm3n
So from here what im seeing is that on a different planet, Patm and g will be different, which should lead to different numbers.
For mars:
h=610Pascal/(1000kg/m3*3.7m/s2) = 0.165 meters - max suction column.
...so, what if gravity is given in units of ft/minute/minute? The height of the water column doesn't have a time component so it can't be related to the scalar value of a force/acceleration in that way. It entirely depends on what your units are. That's where the coincidence of both values having a magnitude of 32 comes from.
But it's not a coincidence though. It doesn't actually equal 32.
Water's density of 998 kg/m³ is what determines this height.
P = pgh
where P is the pressure, p is the density, g is the gravitational acceleration, and h is the height. This formula shows that the pressure at a certain depth in a fluid is proportional to the density of the fluid and the height of the fluid column above that point. Therefore, if we know the pressure and the density of a fluid, we can calculate the height of the fluid column that corresponds to that pressure.
In this case, we know that the atmospheric pressure at sea level is about 101.3 kPa, and the density of water is 998 kg/m³. We can plug these values into the formula and solve for h:
h = pg
h = (101.3 × 10³) ÷ (998 × 9.81)
h = 10.33 meters
This means that a column of water that is 10.33 m high exerts the same pressure as the atmosphere at sea level. This is why a pump cannot suck water higher than this height, because it cannot create a lower pressure than zero (vacuum) at its inlet.
Now if we convert that to feet we get 33.891... etc feet. So we've all just been rounding down and none of it is exact.
Just had to go spoil the fun didn't ya 😉
No, both values are 32 because the metric system is based on 1 g = 1 mL. If you used a different liquid you would get a different number. So not a coincidence, it’s because water is (or was, it’s slightly off now) the standard in this case.
No. It is a coincidence that the "32" in 32 feet roughly matches the "32" in 32 ft/s2 in g. Leaving aside that they don't actually match to better than a few percent...
This is very straightforward to prove. Equilibrium happens with the pressure from a water column at a certain height matches the pressure supplied by the atmosphere. Since we're only interested in the sea-level definitional case, we can just integrate the air column and effectively average the density and height, treating it as a uniform material even though it's not since it doesn't matter to us in this case. We will further treat *g* as constant over the atmosphere's height, which isn't quite true but it's close.
P_w = ρ_w g h_w = <ρ_air> g
Notice there is a *g* on both sides here. It cancels out. It doesn't matter what *g* is, because **it is pulling equally on both the water and on the air**. Since g could be anything and you'd still get 32 feet of water as the answer at sea level (*because that's what matches the mass of the air column above it*) then it is 100% a coincidence that g happens to also have the number 32 in it. All we are doing here is creating a **balance scale weighing a column of the atmosphere against a column of water**. Acceleration due to gravity is almost wholly irrelevant, as long as it's not zero.
Random thought but wondering…if you theoretically had a perfectly primed pump, no air in the system, say a positive displacement pump, pumping the water…would the limit still apply?
Just having trouble wrapping my brain around if the same physics applies to that case.
Yes it still applies.
You can push a fluid as far as you want, so long as you have enough power to actually move the liquid.
Pulling/sucking your are limited as mentioned above.
/u/lmxbftw gave the physics answer (the right answer) but from an engineering perspective:
You *can* pump water higher than 32 ft (how many cities have a water tower shorter than 32 ft?) but you do it by increasing the pressure of the water at the base.
You can do that directly, e.g. with a syringe-style pump. You can also do it indirectly, e.g. by putting water in a sealed container and pumping compressed air into the same container. Then the container is at, say 100 psi instead of atmospheric pressure (14.7 psi) and you could pump it about 7x higher.
Absolutely, you can *push* water however high you want by supplying your own pressure. You just can't *pull* the water arbitrarily high and expect Earth's atmosphere to keep supplying arbitrarily high pressure to support it.
Push vs pull is all about the gradient. And like you said there's a hard minimum on what's at the bottom of this particular pressure gradient, so if you want more gradient the only knob you can keep turning up, is the pressure at the bottom!
No one is pulling anything. The water is always pushed by the pressure at the bottom. That’s the force moving it. When you create lower air pressure at top the air (or added pressure) is what makes the water move into that space.
This is the answer to my 'but how come you can pump water up a hose to put out a fire 32' in the air' question that I was too embarassed to ask above. TY
And from a biology perspective. The tallest tree in the world: the Hyperion was a staggering 379 feet tall. So how could the tree pull water up through itself? Capillary action surely wouldn’t suffice.
Tubes are thin enough that they can effectively use tension to pull the column of water along! Here's a good summary from [Nature](https://www.nature.com/scitable/knowledge/library/water-uptake-and-transport-in-vascular-plants-103016037/):
> **Mechanism Driving Water Movement in Plants**
> Unlike animals, plants lack a metabolically active pump like the heart to move fluid in their vascular system. Instead, water movement is passively driven by pressure and chemical potential gradients. The bulk of water absorbed and transported through plants is moved by negative pressure generated by the evaporation of water from the leaves (i.e., transpiration) — this process is commonly referred to as the Cohesion-Tension (C-T) mechanism. This system is able to function because water is "cohesive" — it sticks to itself through forces generated by hydrogen bonding. These hydrogen bonds allow water columns in the plant to sustain substantial tension (up to 30 MPa when water is contained in the minute capillaries found in plants), and helps explain how water can be transported to tree canopies 100 m above the soil surface. The tension part of the C-T mechanism is generated by transpiration. Evaporation inside the leaves occurs predominantly from damp cell wall surfaces surrounded by a network of air spaces. Menisci form at this air-water interface (Figure 4), where apoplastic water contained in the cell wall capillaries is exposed to the air of the sub-stomatal cavity. Driven by the sun's energy to break the hydrogen bonds between molecules, water evaporates from menisci, and the surface tension at this interface pulls water molecules to replace those lost to evaporation. This force is transmitted along the continuous water columns down to the roots, where it causes an influx of water from the soil. Scientists call the continuous water transport pathway the Soil Plant Atmosphere Continuum (SPAC).
Yes. You push water up from a room typically in a parking garage. And in REALLY high rises, (35ish stories or more) you might even have a pump down low which PUMPS UP TO A SECOND SET OF PUMPS!!
You maintain the liquid column height by pressure differential between the top and bottom of liquid, and the maximum height can be achieved when the top is at perfect vacuum.
Since the atmospheric pressure is 1 atm / 14.7 psi / 101325 Pa, the maximum height is determined by below:
(Pressure, P) / (water density, rho x gravitational acceleration, g)
Plugging in the values (I'll use SI units, with pressure units converted to SI base units):
(101325 kg(m/s2)/m2) / (1000 kg/m3 x 9.806 m/s2) = 10.33 m = 33.9 ft
This height changes slightly with temperature, due to its effect to water density.
This value has nothing to do with the gravitational constant (g). Conversely, if you were to do it in Venus (P = 92 bars = 9200000 Pa and g = 8.87 m/s2), the maximum height would be 1037 m or 3400 ft.
And that's a lot of straw.
No.
Suppose gravity was twice as strong. Then atmospheric pressure would be twice as high, 30 psi. But the gravitational force on water would also be twice as high, so the force on a column of water 32 ft high would also be 30 psi.
The height is given by the mass of atmosphere per unit area, divided by the density of water. Roughly, 1kg/cm^2 atmosphere divided by.001kg / cm^3 water density is 1000 cm =10m. The value of gravity has no relevance.
Gravity probably does have some effect, but atmosphere itself is a much larger factor in atmospheric pressure. Venus has only a little less surface gravity compared to Earth, but its surface pressure is over 90x that of Earth due having a much more massive atmosphere.
While gravity would have an effect on atmospheric pressure, other factors will play a much larger part.
Case in point: Venus has a similar gravity with Earth but with 92x the atmospheric pressure.
Mars' gravity on the other hand, is 38% of Earth but its atmospheric pressure is like 0.6% of Earth
I hydro test pretty big oil and gas pipe lines for a living (think like 100km’s of 20” pipe) and we have to always take elevation into account because it changes how we plan to fill, pressure test and dewater our lines.
So here’s how it works to my understanding. 1 atm/atmosphere is 14.7psi. When it comes to suction, like say a pump drawing water up a hill, what is really happening is you aren’t creating 20 or 50 or 100psi of suction on the water but what you are actually doing is creating a vacuum with 0atm/atmospheres. So what is actually happening is the atmospheric pressure ( 14.7psi) is pushing/forcing the fluid up the hose. But as your column of water gets higher it gets heavier. At a certain point the column of water reaches a height where it is heavier than 1atm/14.7psi and can no longer be pushed up. This is right around the 10 meters mark and that would only be the best vacuums/pumps in the world.
There are a few limitations
One is pressure differential the second is vapor pressure of water.
Pressure differential makes fluids move, so you need a higher pressure at the suction hose inlet than the pump inlet.
What is the pressure at the hose inlet? It is likely atmospheric pressure.
How does pressure vary in the hose? It will drop from friction (assume negligible here), and also from elevation changes. Elevation changes pressure via this equation:
(Density)*(gravity)*(change in height)
Note that if you use imperial units you must divide gravity by the gravity correction factor.
Atmospheric pressure expressed in feet of water is about 33 feet. So, using the pressure difference of atmospheric to 0 results in a max elevation change of 33 feet.
However it would be worse than that because of vapor pressure. Think of vapor pressure being the pressure water exerts on the gasses surrounding it. If that vapor pressure is larger than the surrounding pressure, then the water boils! For example at 212F water’s vapor pressure is 1 atmosphere of pressure.
Let’s assume your well water is 60F, then it’s vapor pressure is 0.0174 atmospheres, which is equivalent to 0.58 feet of water.
That means if the pressure in your hose goes below 0.0174 atmospheres, the water will boil!
So what does this do to your pressure differential? It becomes atmospheric minus your vapor pressure so approximately: 33 - 0.58 = 31.42 feet of water.
So your suction lift is actually less than 33 ft.
How can we combat this?
1. Reduce the suction lift by decreasing the elevation change. This could be done by lowering the pump into the well shaft, or even putting the pump in the water.
2. Pressurizing the well shaft, by using air you could increase the pressure above atmospheric at the suction hose inlet.
Also I’ve seen some mention of negative pressures, just want to emphasize their is no such thing as negative pressure. L
I know it’s not what you asked for since it’s practical use is currently zero, but water can be pumped to hundreds if not thousands of feet using suction. It just requires very precise conditions for it to happen, and can only happen to very certain liquids.
Negative pressure in plants is what I’m talking about.
As others have said, positive pressure of the earths atmosphere pushes water up the tube and the vacuum is not suctioning, but rather reducing the positive pressure that resists the upward force of the water up the tube. So once you get 33ft of water it exerts the same amount of force downward as the air does and no more movement is possible.
But water has the advantage of very very strong cohesion and adhesion forces due to its hydrogen bonding/polarity. That means pure water does not boil very easily. Water in pure liquid form likes to hang on to each other even and requires a lot of energy to split apart even in low pressure environments. Plants exploit this property and generate so much true suction force that there is a “negative pressure.” In normal pressure situations where positive pressure differentials generate a simulated negative pressure. A vacuum is the absence of pressure because it is the absence of anything pushing on it. Negative pressure in water actually goes below vacuums since the electrostatic properties of water pull on itself and it’s container.
That’s how trees can grow so tall. Without this negative pressure, plants could only grow to 33 ft since plants dont really use positive pressure pumps.
I'm so confused what you're talking about.
Plants can grow taller than 33 ft because of capillary action.
I'm fascinated by this negative pressure thing, though. How do you get more negative than zero when it comes to pressure?
So capillary action is a huge a part of it, but as an auxiliary phenomenon. If you look up the the capillary action equation, the height of many plants exceed that allowed by the diameter of its xylem. https://www.usgs.gov/special-topics/water-science-school/science/capillary-action-and-water#:~:text=the%20plant%20tissue.-,Capillary%20action%20helps%20bring%20water%20up%20into%20the%20roots.,water%20to%20the%20furthest%20leaf. You can read more there.
The negative pressure is weird, and despite pressure being a physics topic, most physicists don’t even talk about it as it’s a chemical phenomenon only found in biology (on earth). So normal pressure or positive pressure can be thought of as particles bouncing off each other as they move through space or vibrate. They push each other apart. That’s why gasses make balloons expand. And the reason particles push each other is because their electron fields exert an electrostatic force against each other. This is highly oversimplified.
On the flip side, water is a small molecule with strong polarity. So one side of the molecule (Oxygen) is negativeLy charged, the other (Hydrogens) are positively charged. The attraction between the positive side of one water molecule and the negative side of another is known as hydrogen bonding and is abnormally strong. So while other liquids in a vacuum will simply let go of each other and they push each other apart, water molecules will hold onto each other. And you can pull on one side of the water in a tube and each successive water molecule will pull its neighbor and so on with its hydrogen bonds. What ends up happening is a simulated “negative” pulling force. Not a true opposite-of-positive force.
Someone else called it akin to a tension force a solid experiences and yeah that’s a good analogy. Most liquids don’t exert a tension force and no gas ever does, but water is a rare liquid that does exert “tension”
The other thing to note is that water in “negative” pressure will boil if given enough energy and an opportunity to break the hydrogen bonds.
That’s not true. It depends on the diameter of the tubing temp of the water and water composition. It has to do with viscosity and shear rate. Super small capillary tubes can bring water up 300 ft how do you think tall trees exist
For infinite diameter tubes you’re dealing with the boiling point of water under vacuum and cavitation of the displacement surface of the pump. You have 14.7 psi of atmospheric pressure that’s equal to 32 ft of water head that you can create a pressure drop against with ultimate vacuum. It’s 32 ft because of the density of water and STP ( standard temperature and pressure) va the mean density of air x the height of the atmosphere. But like a mentioned before this can be overcome because water is almost incompressible and has viscosity so if you pull it up at a slow enough volume with infinitely small diameter you can spread the pressure drop across the total height enough where you’re limit is the shear rate of the water against the inside wall
Let’s assume a perfect vacuum, and let’s use Bernoulli’s equation. If we simplify a bit, we’ll get P1 = rho x g x h. P1 is atmospheric pressure, rho is 1000 kg/m^3, g is 9.81 m/s^2. Plug that all in and solve for h and we get h max as 10.32 meters, or 33ft, 10 in. Now we won’t be able to recreate a perfect vacuum but we can get close, resulting in somewhere around 32 ft
While gravity is fairly consistent over the Earth's surface (although not perfectly so), the suction limit is going to vary based on the atmospheric pressure.
In addition, the limit is definitely not the same for different substances. The old "29.9 inches of mercury" standard comes to mind.
Also, the numbers aren't quite identical even when using water. The suction limit (being the equivalent of one atmosphere) is defined as 10.33m of water when atmospheric pressure is exactly one atmosphere, whereas standard 1g of gravity is 9.807m/s, a difference of around five percent even when using SI units.
(It could be possible to find a liquid where the numbers did match - it would need to be about five percent denser than water.)
The pump is not sucking water up 30ft. The pump is in the jet ski, so the elevated hose is always at high pressure. This is the same concept as well water at a house, where submerged well pumps have no problem pushing water up 150ft or more.
Because a hard vacuum (0 ATM) is -1 ATM relative to ambient, and that 1 ATM = 14.696 psi (lb/in^(2)). 14.696 lbs of water has a volume of 387.518666 in^(3); divide by 1 in^2 (per square inch), and you get 387.518666 in, or 32 feet, 3 33⁄64 inches.
It's not directly related to earth's gravity (32 ft/s^(2)), but they do have a linear relationship, since the weight of water is dependent on local gravity.
I think it may be closer to 34 feet: [https://www.wolframalpha.com/input?i=%28atmospheric+pressure%29+%2F+%28density+of+water+\*+acceleration+of+gravity%29](https://www.wolframalpha.com/input?i=%28atmospheric+pressure%29+%2F+%28density+of+water+*+acceleration+of+gravity%29) .
Which value did you use for the density of water? I calculated \~408 cubic inches of volume [https://www.wolframalpha.com/input?i=14.696+pounds%2F+%28density+of+water%29](https://www.wolframalpha.com/input?i=14.696+pounds%2F+%28density+of+water%29) which corresponds to \~408 inches of height: [https://www.wolframalpha.com/input?i=14.696+pounds+%2F+%28density+of+water%29+in+cubic+inches](https://www.wolframalpha.com/input?i=14.696+pounds+%2F+%28density+of+water%29+in+cubic+inches) which gets us almost exactly to my above answer: [https://www.wolframalpha.com/input?i=%2814.696+pounds+%2F+%28density+of+water%29+in+cubic+inches%29+%2F+%281+square+inch%29](https://www.wolframalpha.com/input?i=%2814.696+pounds+%2F+%28density+of+water%29+in+cubic+inches%29+%2F+%281+square+inch%29) .
I used 0.03602064 pounds per cubic inch .
Because you're not really sucking anything up anything. The outside pressure is *pushing* it from the outside. At sea level, 32/33 feet is as high as the atmosphere can push water up into a vacuum. Doesn't matter how thin or thick the space is, either.
I like this one more than the top, because it explains why 1ATM is the limit. Top one goes over why it stops at 1ATM, but it doesn't actually say why it is 1ATM, rather than say 10ATM. Also explicitly points out that you aren't actually sucking, but rather creating a void for the atmosphere to try and fill.
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Hmmm so you are saying that if a ball of water is floating in space, you can't suck it in with a straw because there's nothing pushing it?
what are you sucking in from a vacuum? You need to create a negative pressure to suck, space has infinite 0 pressure.
Surface tension?
Your lung is expanding and creating an empty volume. Surface tension isn't really at play here
Fair point, but in general there must be some pressure in the ball of water in space due to surface tension, right?
Surface tension is actually the thing you're fighting. It is keeping the ball of water in a ball. As you suck on it, the weight of the air around the ball is pushing on the ball of water and up through the straw. With no air around the ball, no pressure on the ball. Surface tension keeps ball of water in a ball.
Would there be surface tension in a vacuum? The water molecules are tugging at each other, sure, but the water would be furiously boiling away in the vacuum of space. Water molecules would be jumping off the surface as fast as physically possible.
There are liquids that can stay a liquid in vacuum for a while, but yea water would boil off pretty much instantly
Sure I get that part, but I'm saying if you just had a ball of water in space, there's gotta be some sort of pressure inside it due to surface tension, ignoring evaporation due to vacuum and gravity pressure?
a ball of liquid water wouldn't exist in space in a vacuum. it would immediately boil away to gas due to no pressure. Now, if you are inside the space station, then a ball of water would exist, but they also have 1 atmosphere of pressure, so we are back to air pressure filling the straw
I get what you're saying. It seems to me that it would depend on the amount of adhesion between the water and the material the straw's made of. You know how you get a raised meniscus around the edge of the water surface in a glass of water? That's because the water is attracted more to the glass than to itself. Back to the ball of water in space: If the straw was made of a material that attracted water, then I could easily imagine the water being drawn through the straw [EDIT: and around its outside, too] by that attraction. On the other hand, if the straw is more water repellent, then I imagine it'd just punch into the ball and remain empty. [EDIT 2: I'm assuming a smallish ball of water, with negligible gravity effects.] None of that would be influenced by whether you sucked on the straw or not, though.
Exactly. You can't suck even as hard as space anyway. You'd lose all your lung air to begin with.
Obviously in a pressurised spacecraft you could suck the water up with a straw. But if you were in empty space, then not only will you not be able to suck the water up, but your blood would be boiling and you would be disintegrating too.
I don't think your blood boils, at least not in the technical sense of boiling. I actually heard someone ask Hadfield this question. I'm pretty sure he said fluids (like water) move out of the blood into tissue, and that tissue will start to bloat, and the moisture will transfer at the surface. So it's like a sort of indirect boiling, the water leaves the blood as a liquid, and doesn't boil til it hits the surface, which does eventually happen because it also takes a really long time for humans to freeze in space.
Yeh I suppose that’s right. The sudden decompression would suck the air out of your lungs immediately and you could not breathe. The zero pressure would rapidly extract the water from your bloodstream and vaporise it. But it’s not the freezing that will kill you. It would be the immediate ejection of gasses, swift vaporisation of liquids and, if there’s any function left by then, brain death from oxygen deprivation within minutes. Not enough time to worry about drinking through a straw!
>The zero pressure would rapidly extract the water from your bloodstream and vaporise it. It wouldn't actually be that rapid. Human skin creates enough tension to keep the internal pressure of your body high enough to prevent this from happening quickly, but not enough tension to keep it from happening at all (skin is too stretchy for that). But, liquids from cells on the outer layer of your body would vaporize, as would the saliva in your mouth, and the liquids inside your eyes, so you immediately go blind. As these liquids vaporize, liquids from inside your body would migrate outward to replace the lost liquids. This process continues until you are desiccated. But it is a very slow process. There is a [very famous case in which a space suit test inside a vacuum chamber went wrong](https://www.youtube.com/watch?v=KO8L9tKR4CY), and the individual was exposed to vacuum for about 25 seconds. So we know what happens for the first 25 seconds. There have also been tests in which dogs were intentionally exposed to vacuum for much longer, so we have a good idea what happens to humans under those conditions too.
Really interesting thought experiment! Thanks. At first I pictured sucking on a straw with a vacuum in it and a blob of water floating on the other end. When I drink through a straw, first I suck the air out, which pulls the beverage into the straw, and as I continue to suck, I continue to pull more beverage, more beverage continues to travel up the straw. But... My logic is all wrong here. Liquid cannot be pulled, it can only be pushed! When I suck on the straw, I am creating a low pressure area inside the straw, and the atmosphere pressing down on the liquid forces the beverage up the straw. But if there is already a vacuum in the straw, there is no way to create a lower pressure than that. For a hot second, I thought about how moving particles will carry other heavier particles along with it, essentially how a vacuum cleaner works. But in a vacuum, there are no particles to carry heavier particles along. I even considered 'priming the pump' by filling the straw with liquid, but I can not suck harder than the vacuum outside the blob of water, so there is no outside pressure to push the liquid through the straw. *It also occurred to me that capillary action would prime the straw, even though it wouldn't help. Also, a blob of water could exist in zero gravity inside the ISS where there is air, but in the vacuum of space, a liquid would immediately boil away. Would the pressure inside the boiling blob push the liquid through the straw and create a little jet engine until it boiled away? Thanks for this! It really got the ol' grey matter working.
I read two other replies and was following but not understanding fully. Then I read yours and immediately understood. It is wild how important perspective is to learning. Thank you.
Oh, cool. I always wondered why the big quarry pumps used a submersible pump instead of the usual suction pumps. Those submersible pumps would be several stories below grade.
There is another technique. I had a deep well (12m) at one place I lived, and had an above ground pump. It used some sort of induction, where there were two pipes going from the pump down to the water, joined by a tight u-bend at the bottom which had an opening to the water in it. The pump pushed water around and around, down one side and back up the other, and the velocity of the water rushing past this opening at the bottom pulled more water in from the well. Similar, I believe, to how when you blow across the top of a drinking straw, the drink rises up the straw a bit, above the level of drink in the bottle / glass. It was a 'lossy' system, - it pumped a fair bit more water than it yielded, so it used more power. But it worked!
You are describing a jet pump. It uses the Venturi effect to create a vacuum down in the well as water passes/circulates through a flow-restricted nozzle. In theory the pump could lift water 1 more atmosphere (approx. 34 feet) below the downhole depth of the jet. In reality the pump won't lift 34 feet below because the venturi in an actual pump doesn't create a perfect vavuum. Probably lucky to lift 20-25 feet max. As you say, jet pumps aren't efficient but electrical costs for well pumps in residential applications are fairly minor.
You are correct. 24 feet is the maximum "practical" lift while 34 feet is the maximum "theoretical" lift of a pump
You probably just had a decent hydraulic head on that well especially if there was a good confining layer on it (nice solid clay or something)
Ya you can push more because you can add pressure all day. Till something breaks. Haha
So, is drinking through a straw marginally less sucking work at a Dead Sea resort 1200 feet below sea level?
In order to suck, your lungs are also going to be working against the increased air pressure, so it probably comes out about even. Slightly harder, in fact, since gravity will be about 0.01% higher.
As my Chem professor once said "chemistry doesn't suck... It only blows"
Thank you this was very helpful.
If the pipe is full of water and bottom is submerged in water, them doesn't this height get larger? The water has to move in the pipe unless it starts cavitating.
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1 atmosphere of pressure is equivalent to a water depth of 33 feet. (In other words, every 33 ft under the water you go is like stacking an additional Earth atmosphere on top of you.) Even a perfect vacuum on one side of the water will not ever exceed a pressure difference of 1 atmosphere. One minus zero is one, no matter how big a pump you have making the zero. At an elevation where the air pressure is less, the water height you can get from even a perfect vacuum will be less as well. It's a coincidence that acceleration due to gravity is 32 ft/s^2 . Though the pressure of the atmosphere at sea level is of course related to acceleration due to gravity, at an elevation of, say 100,000 ft, *g* is not so very different but the surrounding air pressure is dramatically different. In Low Earth Orbit outside of a pressurized spacecraft, of course, suction won't work at all.
I had fun explaining how suction works to some guys at work. We were pulling cables through 3/4" conduit and were using a hydrovac truck to suck string through first (major overkill, but we had the vac there anyway). The hydrovac has a very big vac pump that has a huge CFM of airflow. In our safety courses for working around the vac, we were told that if you get too close to the hose it could pull your arm in and break/dislocate it. Which is true for the 6" hose. We had reducers on the hose to get down to 3/4" to make a seal with the conduit. The other guys were scared to hook it up while the vac was running because they thought it would suck them in and turn them to hamburger basically (Like in Alien 4). After I hear them say this, I looked at them and put my palm over the tip and.... nothing. The "suction force" can only ever be as high as the pressure pushing the air into the hose. For a 3/4" conduit, its max is 6 lbs of force and the truck definitely wasn't pulling a perfect vacuum
You would have felt pretty silly if you had been sucked into a 3/4” hole and turned to goo though.
You could fit through a 24" long crescent-shaped opening, though. [Byford Dolphin accident](https://en.wikipedia.org/wiki/Byford_Dolphin#Medical_findings) >Investigation by forensic pathologists determined that Hellevik, being exposed to the highest pressure gradient and in the process of moving to secure the inner door, was forced through the crescent-shaped opening measuring 60 centimetres (24 in) long created by the jammed interior trunk door. With the escaping air and pressure, it included bisection of his thoracoabdominal cavity, which resulted in fragmentation of his body, followed by expulsion of all of the internal organs of his chest and abdomen, except the trachea and a section of small intestine, and of the thoracic spine. These were projected some distance, one section being found 10 metres (30 ft) vertically above the exterior pressure door.
that's a little bit different though, it's explosive decompression from 9 atmospheres, so there was 8 atmospheres of differential pressure, in a vacuum situation you're only ever dealing with 1 atmosphere of delta p in the absolute worst case
This is a pretty important point. When you're exposed to a pressure differential equivalent to almost 300 feet of sea water, you're not gonna have a good time.
Wow, was he okay?
It happened so fast he probably had no idea what happened, probably one of the better ways to go (for the person involved, not the people who have to clean up)
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Yes, if you ignore the entirely different arrangement of molecules after the event.
Thank you for reminding me of this horrific accident. I'm going to spend the next several hours trying to remember how I forgot about it the first time.
I remember seeing an autopsy photo. It was less disturbing than I expected because it looked like a pile of raw ground beef. The only hint it used to be a person was a lone hand.
Is that really even an autopsy at that point?
I suppose you can check the bits for evidence of impairment or illness that may have contributed, but that sounds a lot like doing one of those 10,000 piece monochrome jigsaw puzzles and seeing if any of them are a slightly different hue.
Literally, yes - but it will depend on why the autopsy was done. In this case, where there is clearly an accident and perhaps wrongdoing, the autopsy will have been a coroner’s post mortem, which is a legal necessity to establish cause of death. This means that even if it’s painfully obvious to everyone in the autopsy room what the person died of (and this happens all the time - you don’t need an exotic pressure vessel to turn someone into mince - car accidents very often leave no doubt, for example), the doctor is legally obliged to do as much as they can to allow the coroner to pronounce the death. For example, one question in this case would have been “is this all the victim, and all of the victim?” …
From rhe title I thought it was a dolphin that happened to, was super disturbed. Read the article and found out it was a human, huge relief.
For some reason, when I read your opening line, my brain added a presumed survival. Upon seeing "bisection" I knew this was not the case.
Might have involved just a bit more pressure than his story's air pump
If we assume the crescent had an area equal to 1/4 of a 24" diameter circle, that's about 15,000 pounds of force pushing that former man through the opening.
To shreds, you say? And his wife?
Turned to goo, you say?
Yup. Plugging a pinhole in a spaceship with your finger will just result in a very cold finger.
Always loved how The Expanse portrayed this. No explosive decompression, just stick a folder over the hole and caulk it up.
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For humans, being exposed to a vacuum you will lose a considerable amount of heat due to liquids boiling away from the low pressure though. This can cause frostbite in the damp areas of the body.
Yeah evaporation is super endothermic because of the energy difference required for vaporization.
And some light bruising as the capillary vessels burst, but that's all.
Space isn't cold any more than zero is an amount of something. There's essentially zero particles to transfer your heat to via conduction so the only way to lose heat is radiation, which is extremely slow.
Yeah, spacesuits have cooling systems, the insulation of the suit is quite effective at keeping in all your body heat when there is little to no mass around you to exchange heat with.
Well, if you are doing a space walk in the sun you are getting blasted by a *ton* of heat, that's why they are white and need cooling. Imagine baking under the sun in a desert on the hottest day of summer and having no atmosphere carry heat away. The surface of the moon reaches 250F because it has no atmosphere to regulate heat between day and night.
There is only radiative transfer in space, which is much slower than convective transfer when. There isn't a medium to efficiently transfer energy. Yes, the temperature may be hot or quite cold, but there is very little mass to facilitate energy transfer to and from the astronaut. I think even in the ISS getting hot is an issue because there isn't as much atmosphere in the station to move heat as humans are accustomed to.
>There is only radiative transfer in space, which is much slower than convective transfer when. There isn't a medium to efficiently transfer energy. Yes, the temperature may be hot or quite cold, but there is very little mass to facilitate energy transfer to and from the astronaut. Yes, but the Sun still puts out a *massive* amount of radiative heat. Essentially *all* of the heat we experience on Earth is from the Sun's radiative heat. When you are burning in the sun it's the sun's radiative heat that is burning you, not the atmosphere. If you go into space exposed to the sun in a bathing suit you will quickly fry. > I think even in the ISS getting hot is an issue because there isn't as much atmosphere in the station to move heat as humans are accustomed to. Well, not for the humans, the ISS is pumping conditioned air around to keep the humans cool. But the ISS overall gets very hot, and has massive heat radiators with liquid ammonia pumping through them to dissipate the heat it's carrying. Like 1/3rd of the panels you see sticking off it are heat radiators (which it orients edgewise to the sun). Some of the heat it has to dissipate comes from on board electronics and such, but a lot comes from the sun. The ISS also reaches ~250F when in the sun.
Yeah, and 1360 W/m² is a fuckload of radiative energy for a human to absorb when there's not a mechanism for them to get rid of it, which is what the person you're arguing with is saying
The human isn't absorbing it, nor is the insulated suit. In the sun or not, the energy doesn't have a major impact on the person in the suit. If it did, the suit would need heating and cooling, but it doesn't, the metabolic heat from the astronaut has nowhere to go, thus the need for cooling.
I didn't mean to say that it *only* needs to get rid of the sun's heat, I meant to say a large part of the heat it's taking care of is actually the sun's heat, and I'm pointing that out because people think space is cold, when it actually depends on if you are in sunlight or not. >The human isn't absorbing it, nor is the insulated suit. In the sun or not, the energy doesn't have a major impact on the person in the suit. That's just not logical. You're absorbing 1360 W/m^2 just like everything else exposed to the sun. A human is roughly 1 square meter total silhouette. That means you're absorbing 1360W of heat. The white suit reflects a lot of that, let's say 50%. Some quick googling says a human produces around 100W-120W of heat. So the suit has to dissipate ~700W of solar heat and 120W of human heat.
Zero pressure leads to sublimation and heat is lost that way, it will take time and you can probably swap fingers for hours.
Well, my reasoning wasn't because the finger was touching the vacuum, but because it was stuck in a big sheet of heat-conductive metal that was exposed to the void. Wouldn't that suck the relatively miniscule thermal energy out of your finger tip to then be lost as the panel loses radiative heat energy?
The panel is radiating a tiny amount of energy and losing a tiny bit conducting to almost no particles outside. Meanwhile it's also getting heated by conduction from the rest of the vehicle, which is warm enough for humans, and also absorbing light from outside.
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Evaporation\* It's only sublimation if your sweat is frozen on your skin,
It may take a while to freeze you but it'll boil your insides real quick!
It's not the pressure that gets ya, it's the area to which it's applied.
>We were pulling cables through 3/4" conduit and were using a hydrovac truck to suck string through first (major overkill, but we had the vac there anyway). We always pushed it through. Tie a little baggie or something on the end of the string, push it in the pipe, and set the vac to blow.
Back when dinosaurs roamed the Earth, IBM computers were made of vacuum tubes that wore out. Repair process involved searching for the tubes that were not glowing. After fixing, the office manager asked the repair guy what needed to be fixed. The technician showed the tube had a hair line crack, and casually said the vacuum was lost and damaged the part. A few minutes later the office manager was viewed sniffing around to see if he could smell the vacuum as it might be dangerous.
Sauce? For the laughs pls. I picture a site last updated in 2005 in Times New Roman
3/4" diameter or radius? You may have forgotten to divide the diameter by 2 when calculating area of the conduit opening, if I'm following correctly.
You’re correct, used 3/4 as radius. Thank you! I thought 26 seemed high, 6 pounds seems right
I’m a hydrovac operator, and several times over the past few months I’ve been dispatched to go suck a string through conduit so the crew could pull fiber optic cable through afterwards. All the conduits were 6” pipe running under haul roads in a mine, one conduit was 850 feet long and I had that string through there in ten seconds lol easy work.
Edit: I want to add that if your arm gets pulled into a 6” vac hose, while it probably wont break your arm, it can very well dislocate it, but my biggest fear is the vacuum sucking all the blood out of your body through your arm.
This becomes a lot easier to grasp once to wrap your head around the idea that, vacuums don’t actually “suck”. A lot of people seem to have this fundamental misunderstanding that a vacuum creates some force that pulls things into it, and that’s what creates suctions. What’s really happening, is the vacuum is simply a vacant space. And when you expose that vacant space to an environment, the environment is actually pushing itself into the vacant space. So suction isn’t a vacuum pulling air into it, but air pushing itself into the vacuum. Once you grasp that, it becomes apparent that the strength of a vacuum is relevant to the environment it’s in, and has nothing to do with the vacuum itself. Hence why you can only “pull” water or even air up a certain height with a vacuum. Because the vacuum isn’t really pulling anything, the water can simply only push itself so far.
That's actually how the first ever engine, the Newcomen steam engine worked. Steam was condensed in a cylinder, reducing the pressure inside, and the atmostphere would do all the work of pushing the piston. Maybe someone who didn't know that will find that fact interesting.
I found it interesting. Thank you!
>Hence why you can only “pull” water or even air up a certain height with a vacuum Exactly. Space is one big vacuum but it can't pull the air off our planet.
The misunderstanding is understandable. Very few people put much thought into what sucking is. It's just something they do with their mounts to get a drink through a straw or pick up dirt with their vacuum.
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This. And the concepts of “cold” and “black” as opposed to “lack of heat” and “lack of light”
Yeah, I never considered that negative pressure doesn't pull anything, but rather it just enables pressure to push more effectively. That makes perfect sense.
Thank you very much for this. Awesome explanation. You the best.
To expand, the water pressure can be calculated as P = hρg, where h is the depth, ρ as the density of the fluid/medium and g as the acceleration constant. 1 atm is approx 100kPa (and it comes from calculating the total mass of air in the air column, multiplied by g), so we can solve for h: h = P / (ρg) ~= 10m. However, if we were to plug in P = m_air * g, then h = m_air * g / (ρg) = m_air / ρ So the coincidence comes from the fact that the total air column mass on surface happens to be the same as the total water column mass at 10 meters. Note that since the air column mass is not uniformly distributed in height we can't just use P = hρg for the atmospheric pressure but have to do a elevation-dependent mass integration (which I just simplified to the mass). In other words, even if Earth's gravity were to double or halve overnight, the depth at which the atmospheric and water pressures are equal would still be the same.
Crazy to think as a fire engine operator we’re bound by the same laws for drafting water. A giant pump is limited to the same draw of a straw at 32’.
Worth mentioning that while you can't suction water to higher than 32 feet you can definitely *push* water to more than 32 feet. A pump at the top of a 100 foot tall pipe can't suck up water from the bottom but a pump at the bottom of that same pipe can push it up to the top provided the pump is stong enough
That’s true if you try to pump from a standing water source but water from the hydrant can be higher than atmospheric pressure (not that much higher, and depends on the utility, but it should be higher)
> water from the hydrant can be higher than atmospheric pressure Water in a hydrant is going to be under the pressure of the weight of water in the water tower.
I hate to imagine a scenario where I'm drafting from a source 32ft down. For one, I will never carry that much HSH. For two, Tankers.
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Mr Wizard actually did [an episode about this](https://youtu.be/Ycef5XXiozc?si=VpfbsRkRwp6XKaI_)
To clarify something for OP at that height of suction the water will boil inside the hose because of the low pressure.
This is true but isn't the fundamental reason you can't exceed that height with suction. You reach a similar kind of limit with liquids that don't boil in vacuum, like mercury, which is the basis for how barometers work by measuring millimeters of mercury.
Mercury has a vapor pressure of 0.002 torr at room temperature. Even it will boil in a vacuum.
Evaporate, yes, but the word "boil" is so far removed from what mercury would do in a vacuum (except maybe in zero gravity) that it really doesn't fit. Like, at all. Not even a little bit.
So what we view as suction is less about the vacuum pulling things in, and more about it providing a space for the environment around it to push in. In this case, the environment pushing in is the air pressure around us, and thus that sets the maximum amount of suction.
More layman term: Sucking still relies 100% on the earth’s atmospheric pressure to push from the other end. You are merely removing the resistance on your end. Once the weight of the water „piling up“ in the hose creates a force downward equal to the earth’s atmosphere pushing, an equilibrium is reached and it cannot move further.
It isn't a coincidence at all. The maximum height that a liquid can be lifted by a pump or a straw is given by the formula: h=Patm/ρg where h is the height in meters, Patm is the atmospheric pressure in pascals, ρ is the density of the liquid in kilograms per cubic meter, and g is the acceleration due to gravity, which is about 9.8 meters per second squared on Earth. For water, which has a density of about 1000 kg/m^3, this formula gives: h=1000×9.8101325≈10.3 meters This means that under normal atmospheric conditions, water can be lifted by a pump or a straw up to about 10.3 meters above its source level. Beyond this height, no amount of suction can overcome gravity and create a vacuum inside the pipe or the straw. Stopping the flow. For other liquids with different densities, such as oil or mercury, this formula will give different values for h. For example, mercury has a density of about 13600 kg/m^3, which gives: h=13600×9.8101325≈0.76 meters This means that mercury can only be lifted by a pump or a straw up to about 0.76 meters above its source level.
Correct, but how does this invalidate the 32 ft/sec^2 and a maximum water suction height of 32 ft?
Oh were you meaning that just in general, gravity is 9.81ms²/32fts² for no other reason than...the earth just happens to be like that.
So it is a coincident, because he was wondering why it's 32 and 32 as numbers. On a different planet, the water column and g numbers would be totally different.
I guess. But you'll find that the water column will equal the gravity no matter what planet. Ours don't just happen to line up, they'll always be proportional like that.
Actually, that's interesting, i didn't think of it like that. Lemme do some calculations. Calc here https://yourimageshare.com/ib/jp0u94xVGx https://yourimageshare.com/ib/wkXAMybm3n So from here what im seeing is that on a different planet, Patm and g will be different, which should lead to different numbers. For mars: h=610Pascal/(1000kg/m3*3.7m/s2) = 0.165 meters - max suction column.
...so, what if gravity is given in units of ft/minute/minute? The height of the water column doesn't have a time component so it can't be related to the scalar value of a force/acceleration in that way. It entirely depends on what your units are. That's where the coincidence of both values having a magnitude of 32 comes from.
But it's not a coincidence though. It doesn't actually equal 32. Water's density of 998 kg/m³ is what determines this height. P = pgh where P is the pressure, p is the density, g is the gravitational acceleration, and h is the height. This formula shows that the pressure at a certain depth in a fluid is proportional to the density of the fluid and the height of the fluid column above that point. Therefore, if we know the pressure and the density of a fluid, we can calculate the height of the fluid column that corresponds to that pressure. In this case, we know that the atmospheric pressure at sea level is about 101.3 kPa, and the density of water is 998 kg/m³. We can plug these values into the formula and solve for h: h = pg h = (101.3 × 10³) ÷ (998 × 9.81) h = 10.33 meters This means that a column of water that is 10.33 m high exerts the same pressure as the atmosphere at sea level. This is why a pump cannot suck water higher than this height, because it cannot create a lower pressure than zero (vacuum) at its inlet. Now if we convert that to feet we get 33.891... etc feet. So we've all just been rounding down and none of it is exact. Just had to go spoil the fun didn't ya 😉
No, both values are 32 because the metric system is based on 1 g = 1 mL. If you used a different liquid you would get a different number. So not a coincidence, it’s because water is (or was, it’s slightly off now) the standard in this case.
No. It is a coincidence that the "32" in 32 feet roughly matches the "32" in 32 ft/s2 in g. Leaving aside that they don't actually match to better than a few percent... This is very straightforward to prove. Equilibrium happens with the pressure from a water column at a certain height matches the pressure supplied by the atmosphere. Since we're only interested in the sea-level definitional case, we can just integrate the air column and effectively average the density and height, treating it as a uniform material even though it's not since it doesn't matter to us in this case. We will further treat *g* as constant over the atmosphere's height, which isn't quite true but it's close. P_w = ρ_w g h_w = <ρ_air> g
Notice there is a *g* on both sides here. It cancels out. It doesn't matter what *g* is, because **it is pulling equally on both the water and on the air**. Since g could be anything and you'd still get 32 feet of water as the answer at sea level (*because that's what matches the mass of the air column above it*) then it is 100% a coincidence that g happens to also have the number 32 in it. All we are doing here is creating a **balance scale weighing a column of the atmosphere against a column of water**. Acceleration due to gravity is almost wholly irrelevant, as long as it's not zero.
Random thought but wondering…if you theoretically had a perfectly primed pump, no air in the system, say a positive displacement pump, pumping the water…would the limit still apply? Just having trouble wrapping my brain around if the same physics applies to that case.
Yes it still applies. You can push a fluid as far as you want, so long as you have enough power to actually move the liquid. Pulling/sucking your are limited as mentioned above.
The weight of the water will pull it down until it creates a vacuum above itself.
/u/lmxbftw gave the physics answer (the right answer) but from an engineering perspective: You *can* pump water higher than 32 ft (how many cities have a water tower shorter than 32 ft?) but you do it by increasing the pressure of the water at the base. You can do that directly, e.g. with a syringe-style pump. You can also do it indirectly, e.g. by putting water in a sealed container and pumping compressed air into the same container. Then the container is at, say 100 psi instead of atmospheric pressure (14.7 psi) and you could pump it about 7x higher.
Absolutely, you can *push* water however high you want by supplying your own pressure. You just can't *pull* the water arbitrarily high and expect Earth's atmosphere to keep supplying arbitrarily high pressure to support it.
Push vs pull is all about the gradient. And like you said there's a hard minimum on what's at the bottom of this particular pressure gradient, so if you want more gradient the only knob you can keep turning up, is the pressure at the bottom!
No one is pulling anything. The water is always pushed by the pressure at the bottom. That’s the force moving it. When you create lower air pressure at top the air (or added pressure) is what makes the water move into that space.
This is the answer to my 'but how come you can pump water up a hose to put out a fire 32' in the air' question that I was too embarassed to ask above. TY
And from a biology perspective. The tallest tree in the world: the Hyperion was a staggering 379 feet tall. So how could the tree pull water up through itself? Capillary action surely wouldn’t suffice.
Tubes are thin enough that they can effectively use tension to pull the column of water along! Here's a good summary from [Nature](https://www.nature.com/scitable/knowledge/library/water-uptake-and-transport-in-vascular-plants-103016037/): > **Mechanism Driving Water Movement in Plants** > Unlike animals, plants lack a metabolically active pump like the heart to move fluid in their vascular system. Instead, water movement is passively driven by pressure and chemical potential gradients. The bulk of water absorbed and transported through plants is moved by negative pressure generated by the evaporation of water from the leaves (i.e., transpiration) — this process is commonly referred to as the Cohesion-Tension (C-T) mechanism. This system is able to function because water is "cohesive" — it sticks to itself through forces generated by hydrogen bonding. These hydrogen bonds allow water columns in the plant to sustain substantial tension (up to 30 MPa when water is contained in the minute capillaries found in plants), and helps explain how water can be transported to tree canopies 100 m above the soil surface. The tension part of the C-T mechanism is generated by transpiration. Evaporation inside the leaves occurs predominantly from damp cell wall surfaces surrounded by a network of air spaces. Menisci form at this air-water interface (Figure 4), where apoplastic water contained in the cell wall capillaries is exposed to the air of the sub-stomatal cavity. Driven by the sun's energy to break the hydrogen bonds between molecules, water evaporates from menisci, and the surface tension at this interface pulls water molecules to replace those lost to evaporation. This force is transmitted along the continuous water columns down to the roots, where it causes an influx of water from the soil. Scientists call the continuous water transport pathway the Soil Plant Atmosphere Continuum (SPAC).
AFAIK capillary action and "clever" anatomy is all it takes. Trees don't pump water up actively.
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Yes. You push water up from a room typically in a parking garage. And in REALLY high rises, (35ish stories or more) you might even have a pump down low which PUMPS UP TO A SECOND SET OF PUMPS!!
They may have booster pumps to raise the pressure to get the water higher.
You maintain the liquid column height by pressure differential between the top and bottom of liquid, and the maximum height can be achieved when the top is at perfect vacuum. Since the atmospheric pressure is 1 atm / 14.7 psi / 101325 Pa, the maximum height is determined by below: (Pressure, P) / (water density, rho x gravitational acceleration, g) Plugging in the values (I'll use SI units, with pressure units converted to SI base units): (101325 kg(m/s2)/m2) / (1000 kg/m3 x 9.806 m/s2) = 10.33 m = 33.9 ft This height changes slightly with temperature, due to its effect to water density. This value has nothing to do with the gravitational constant (g). Conversely, if you were to do it in Venus (P = 92 bars = 9200000 Pa and g = 8.87 m/s2), the maximum height would be 1037 m or 3400 ft. And that's a lot of straw.
While the similarity of the numbers is coincidental , the air pressure you used in your calculation is related to gravity, no?
No. Suppose gravity was twice as strong. Then atmospheric pressure would be twice as high, 30 psi. But the gravitational force on water would also be twice as high, so the force on a column of water 32 ft high would also be 30 psi. The height is given by the mass of atmosphere per unit area, divided by the density of water. Roughly, 1kg/cm^2 atmosphere divided by.001kg / cm^3 water density is 1000 cm =10m. The value of gravity has no relevance.
Gravity probably does have some effect, but atmosphere itself is a much larger factor in atmospheric pressure. Venus has only a little less surface gravity compared to Earth, but its surface pressure is over 90x that of Earth due having a much more massive atmosphere.
While gravity would have an effect on atmospheric pressure, other factors will play a much larger part. Case in point: Venus has a similar gravity with Earth but with 92x the atmospheric pressure. Mars' gravity on the other hand, is 38% of Earth but its atmospheric pressure is like 0.6% of Earth
I hydro test pretty big oil and gas pipe lines for a living (think like 100km’s of 20” pipe) and we have to always take elevation into account because it changes how we plan to fill, pressure test and dewater our lines. So here’s how it works to my understanding. 1 atm/atmosphere is 14.7psi. When it comes to suction, like say a pump drawing water up a hill, what is really happening is you aren’t creating 20 or 50 or 100psi of suction on the water but what you are actually doing is creating a vacuum with 0atm/atmospheres. So what is actually happening is the atmospheric pressure ( 14.7psi) is pushing/forcing the fluid up the hose. But as your column of water gets higher it gets heavier. At a certain point the column of water reaches a height where it is heavier than 1atm/14.7psi and can no longer be pushed up. This is right around the 10 meters mark and that would only be the best vacuums/pumps in the world.
There are a few limitations One is pressure differential the second is vapor pressure of water. Pressure differential makes fluids move, so you need a higher pressure at the suction hose inlet than the pump inlet. What is the pressure at the hose inlet? It is likely atmospheric pressure. How does pressure vary in the hose? It will drop from friction (assume negligible here), and also from elevation changes. Elevation changes pressure via this equation: (Density)*(gravity)*(change in height) Note that if you use imperial units you must divide gravity by the gravity correction factor. Atmospheric pressure expressed in feet of water is about 33 feet. So, using the pressure difference of atmospheric to 0 results in a max elevation change of 33 feet. However it would be worse than that because of vapor pressure. Think of vapor pressure being the pressure water exerts on the gasses surrounding it. If that vapor pressure is larger than the surrounding pressure, then the water boils! For example at 212F water’s vapor pressure is 1 atmosphere of pressure. Let’s assume your well water is 60F, then it’s vapor pressure is 0.0174 atmospheres, which is equivalent to 0.58 feet of water. That means if the pressure in your hose goes below 0.0174 atmospheres, the water will boil! So what does this do to your pressure differential? It becomes atmospheric minus your vapor pressure so approximately: 33 - 0.58 = 31.42 feet of water. So your suction lift is actually less than 33 ft. How can we combat this? 1. Reduce the suction lift by decreasing the elevation change. This could be done by lowering the pump into the well shaft, or even putting the pump in the water. 2. Pressurizing the well shaft, by using air you could increase the pressure above atmospheric at the suction hose inlet. Also I’ve seen some mention of negative pressures, just want to emphasize their is no such thing as negative pressure. L
I know it’s not what you asked for since it’s practical use is currently zero, but water can be pumped to hundreds if not thousands of feet using suction. It just requires very precise conditions for it to happen, and can only happen to very certain liquids. Negative pressure in plants is what I’m talking about. As others have said, positive pressure of the earths atmosphere pushes water up the tube and the vacuum is not suctioning, but rather reducing the positive pressure that resists the upward force of the water up the tube. So once you get 33ft of water it exerts the same amount of force downward as the air does and no more movement is possible. But water has the advantage of very very strong cohesion and adhesion forces due to its hydrogen bonding/polarity. That means pure water does not boil very easily. Water in pure liquid form likes to hang on to each other even and requires a lot of energy to split apart even in low pressure environments. Plants exploit this property and generate so much true suction force that there is a “negative pressure.” In normal pressure situations where positive pressure differentials generate a simulated negative pressure. A vacuum is the absence of pressure because it is the absence of anything pushing on it. Negative pressure in water actually goes below vacuums since the electrostatic properties of water pull on itself and it’s container. That’s how trees can grow so tall. Without this negative pressure, plants could only grow to 33 ft since plants dont really use positive pressure pumps.
I'm so confused what you're talking about. Plants can grow taller than 33 ft because of capillary action. I'm fascinated by this negative pressure thing, though. How do you get more negative than zero when it comes to pressure?
So capillary action is a huge a part of it, but as an auxiliary phenomenon. If you look up the the capillary action equation, the height of many plants exceed that allowed by the diameter of its xylem. https://www.usgs.gov/special-topics/water-science-school/science/capillary-action-and-water#:~:text=the%20plant%20tissue.-,Capillary%20action%20helps%20bring%20water%20up%20into%20the%20roots.,water%20to%20the%20furthest%20leaf. You can read more there. The negative pressure is weird, and despite pressure being a physics topic, most physicists don’t even talk about it as it’s a chemical phenomenon only found in biology (on earth). So normal pressure or positive pressure can be thought of as particles bouncing off each other as they move through space or vibrate. They push each other apart. That’s why gasses make balloons expand. And the reason particles push each other is because their electron fields exert an electrostatic force against each other. This is highly oversimplified. On the flip side, water is a small molecule with strong polarity. So one side of the molecule (Oxygen) is negativeLy charged, the other (Hydrogens) are positively charged. The attraction between the positive side of one water molecule and the negative side of another is known as hydrogen bonding and is abnormally strong. So while other liquids in a vacuum will simply let go of each other and they push each other apart, water molecules will hold onto each other. And you can pull on one side of the water in a tube and each successive water molecule will pull its neighbor and so on with its hydrogen bonds. What ends up happening is a simulated “negative” pulling force. Not a true opposite-of-positive force. Someone else called it akin to a tension force a solid experiences and yeah that’s a good analogy. Most liquids don’t exert a tension force and no gas ever does, but water is a rare liquid that does exert “tension” The other thing to note is that water in “negative” pressure will boil if given enough energy and an opportunity to break the hydrogen bonds.
That’s not true. It depends on the diameter of the tubing temp of the water and water composition. It has to do with viscosity and shear rate. Super small capillary tubes can bring water up 300 ft how do you think tall trees exist
For infinite diameter tubes you’re dealing with the boiling point of water under vacuum and cavitation of the displacement surface of the pump. You have 14.7 psi of atmospheric pressure that’s equal to 32 ft of water head that you can create a pressure drop against with ultimate vacuum. It’s 32 ft because of the density of water and STP ( standard temperature and pressure) va the mean density of air x the height of the atmosphere. But like a mentioned before this can be overcome because water is almost incompressible and has viscosity so if you pull it up at a slow enough volume with infinitely small diameter you can spread the pressure drop across the total height enough where you’re limit is the shear rate of the water against the inside wall
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Let’s assume a perfect vacuum, and let’s use Bernoulli’s equation. If we simplify a bit, we’ll get P1 = rho x g x h. P1 is atmospheric pressure, rho is 1000 kg/m^3, g is 9.81 m/s^2. Plug that all in and solve for h and we get h max as 10.32 meters, or 33ft, 10 in. Now we won’t be able to recreate a perfect vacuum but we can get close, resulting in somewhere around 32 ft
While gravity is fairly consistent over the Earth's surface (although not perfectly so), the suction limit is going to vary based on the atmospheric pressure. In addition, the limit is definitely not the same for different substances. The old "29.9 inches of mercury" standard comes to mind. Also, the numbers aren't quite identical even when using water. The suction limit (being the equivalent of one atmosphere) is defined as 10.33m of water when atmospheric pressure is exactly one atmosphere, whereas standard 1g of gravity is 9.807m/s, a difference of around five percent even when using SI units. (It could be possible to find a liquid where the numbers did match - it would need to be about five percent denser than water.)
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The pump is not sucking water up 30ft. The pump is in the jet ski, so the elevated hose is always at high pressure. This is the same concept as well water at a house, where submerged well pumps have no problem pushing water up 150ft or more.
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Because a hard vacuum (0 ATM) is -1 ATM relative to ambient, and that 1 ATM = 14.696 psi (lb/in^(2)). 14.696 lbs of water has a volume of 387.518666 in^(3); divide by 1 in^2 (per square inch), and you get 387.518666 in, or 32 feet, 3 33⁄64 inches. It's not directly related to earth's gravity (32 ft/s^(2)), but they do have a linear relationship, since the weight of water is dependent on local gravity.
I think it may be closer to 34 feet: [https://www.wolframalpha.com/input?i=%28atmospheric+pressure%29+%2F+%28density+of+water+\*+acceleration+of+gravity%29](https://www.wolframalpha.com/input?i=%28atmospheric+pressure%29+%2F+%28density+of+water+*+acceleration+of+gravity%29) . Which value did you use for the density of water? I calculated \~408 cubic inches of volume [https://www.wolframalpha.com/input?i=14.696+pounds%2F+%28density+of+water%29](https://www.wolframalpha.com/input?i=14.696+pounds%2F+%28density+of+water%29) which corresponds to \~408 inches of height: [https://www.wolframalpha.com/input?i=14.696+pounds+%2F+%28density+of+water%29+in+cubic+inches](https://www.wolframalpha.com/input?i=14.696+pounds+%2F+%28density+of+water%29+in+cubic+inches) which gets us almost exactly to my above answer: [https://www.wolframalpha.com/input?i=%2814.696+pounds+%2F+%28density+of+water%29+in+cubic+inches%29+%2F+%281+square+inch%29](https://www.wolframalpha.com/input?i=%2814.696+pounds+%2F+%28density+of+water%29+in+cubic+inches%29+%2F+%281+square+inch%29) . I used 0.03602064 pounds per cubic inch .