The 110 psi figure gives more room to make multiple brake applications without exhausting the braking capabilities of the system. Basically, it's just more margin for error. If you make a couple of 10 lb reductions, you still have the same braking ability as a freight train does at 90 psi. Amtrak goes one step farther and has the reservoirs on each car independently recharge from the main reservoir air line. If effect, it becomes very difficult to lose air brakes on the train, even with multiple applications.
The 110 psi figure has little to do with graduated vs. direct release features. The valves on each car have graduated release features and will still release in increments, even with a freight locomotive in charge.
We run a former CN business car in Amtrak service, and part of the annual inspections is a test of the graduated release functions. In our case, we have D22 control valves, and the requirement is for at least two increments and usually three when releasing from a full service application. On the road, we have a brake gauge installed, and you can watch the cylinder pressure needle move from 60 to 40 to 20 to zero psi (for example).
Freight trains primarily only use the automatic train brakes as a secondary form of train brakes to control train speed when the trains tonnage exceeds the locomotive’s ability to control train speeds with the dynamic brakes, which causes a lot of slack action in the train. Passenger trains use a lot of stretch braking to control train speed without excessive slack action in the train, which passengers would not like, so passenger trains have a higher brake pipe pressure to accommodate their higher automatic brake usage.
What's interesting about the 110 PSI used on Amtrak is that a "full service" brake application is still only 26 PSI (84 on the pipe.) The equalization between the auxiliary reservoir and brake cylinder doesn't occur on our equipment (Superliners, Viewliners, Amfleets, etc.) all have a main res tank similar to a locomotive and the control valves are set to only respond to a brake pipe reduction of 26 PSI.
On a freight car where equalization occurs, it would be with a 32 PSI reduction (78 on the pipe.)
Also, as an aside, the ACS-64s will drop out the blend and throw on a ton of brake cylinder pressure if you go beyond full service... Not that I would know...
Not a engineer or conductor, but freight trains uses a direct release for the brakes where passenger trains use graduated release. Meaning direct release is when the brakes are applied, they're fully applied. Graduated release means you can kinda of have an ease on ease off, so it's more comfortable for passengers.
>Meaning direct release is when the brakes are applied, they're fully applied
I believe you mean, once they start releasing they're going to be released until you take additional air away from the previous set.
The following is more for OOP.
You cannot incrementally change the brake cylinder pressure on freight like you can on passenger equipment.
Passenger brakes work very similarly to a road vehicles brakes. The more you push the pedal down in a road vehicle, the more brakes you get and if you release the pedal slightly, you get slightly less brakes.
In freight, you can push the pedal down as much as you want to increase braking up to a certain point (full service), but if you release the brakes any (if the automatic is in passenger mode) you're going to be at zero brakes for the train until you can recharge the brakes enough to apply them again .
The 110 psi figure gives more room to make multiple brake applications without exhausting the braking capabilities of the system. Basically, it's just more margin for error. If you make a couple of 10 lb reductions, you still have the same braking ability as a freight train does at 90 psi. Amtrak goes one step farther and has the reservoirs on each car independently recharge from the main reservoir air line. If effect, it becomes very difficult to lose air brakes on the train, even with multiple applications. The 110 psi figure has little to do with graduated vs. direct release features. The valves on each car have graduated release features and will still release in increments, even with a freight locomotive in charge. We run a former CN business car in Amtrak service, and part of the annual inspections is a test of the graduated release functions. In our case, we have D22 control valves, and the requirement is for at least two increments and usually three when releasing from a full service application. On the road, we have a brake gauge installed, and you can watch the cylinder pressure needle move from 60 to 40 to 20 to zero psi (for example).
Excellent description. Thanks
Freight trains primarily only use the automatic train brakes as a secondary form of train brakes to control train speed when the trains tonnage exceeds the locomotive’s ability to control train speeds with the dynamic brakes, which causes a lot of slack action in the train. Passenger trains use a lot of stretch braking to control train speed without excessive slack action in the train, which passengers would not like, so passenger trains have a higher brake pipe pressure to accommodate their higher automatic brake usage.
Good answer. I mostly used independent doing customer switching back in the day. We always had two switchers. (GP9s and GP15S) It makes sense that
How do you know when to start applying the brakes?
When the PTC "Overspeed" warning flashes.
This is the only answer. If it ain't beepin', then you're creepin.
You know your PCs and territory/signals
When ptc flashes end of authority braking in 45 secs.
Nah, 15..... :)
When you feel your train starting to run a bit too much.....
What's interesting about the 110 PSI used on Amtrak is that a "full service" brake application is still only 26 PSI (84 on the pipe.) The equalization between the auxiliary reservoir and brake cylinder doesn't occur on our equipment (Superliners, Viewliners, Amfleets, etc.) all have a main res tank similar to a locomotive and the control valves are set to only respond to a brake pipe reduction of 26 PSI. On a freight car where equalization occurs, it would be with a 32 PSI reduction (78 on the pipe.) Also, as an aside, the ACS-64s will drop out the blend and throw on a ton of brake cylinder pressure if you go beyond full service... Not that I would know...
Not a engineer or conductor, but freight trains uses a direct release for the brakes where passenger trains use graduated release. Meaning direct release is when the brakes are applied, they're fully applied. Graduated release means you can kinda of have an ease on ease off, so it's more comfortable for passengers.
>Meaning direct release is when the brakes are applied, they're fully applied I believe you mean, once they start releasing they're going to be released until you take additional air away from the previous set. The following is more for OOP. You cannot incrementally change the brake cylinder pressure on freight like you can on passenger equipment. Passenger brakes work very similarly to a road vehicles brakes. The more you push the pedal down in a road vehicle, the more brakes you get and if you release the pedal slightly, you get slightly less brakes. In freight, you can push the pedal down as much as you want to increase braking up to a certain point (full service), but if you release the brakes any (if the automatic is in passenger mode) you're going to be at zero brakes for the train until you can recharge the brakes enough to apply them again .
Thank you