Air Brake Question

[Smokey N Steamer]

Hi. I am still relatively new to this hobby and I am seeking some guidance. When it comes to automatic air brakes, what are typical maximum trainline pressures?

[mjahn]

Very few people run automatic brakes but David Sclavi developed a triple valve and has auto brakes on his rolling stock. You can find him on this board or if you search Mercer Locomotive Works on the web. Most straight air applied brake systems run around 65 lbs and achieve sufficient braking effort.

[cbrew]

99% of the automatic air brakes that i have seen and read about are the balanced system. must that i have talked to here on the west coast run 40 to 50 psi, this includes my train. this allows for use of steam pumps
the goal is to allow interchangeability.


what other questions do you have

The system that dave developed with a triple valve is cool but i seem to remember the pressures are high,

[mjahn]

Cbrew,

You run auto brakes?

[cbrew]

yes sir,

[RCW]

yes sir,

Please elaborate.

[cbrew]

well, its late but i can get started with the following,

The system i use is the balanced system,
this system uses a double acting air cylinder
One side of the piston is connected to the train line, (non piston rod)
the other side of cylinder is connected to a storage tank on the car that is fed via the train line throw a check valve, (piston rod)

when the train line is up to working pressure and the two sides balance out, and because the of volume difference created be the piston rod,
the action will favor that side and extend the rod.
once the pressure is dropped in the train line, with the natural balancing the piston rod will retract
pulling on the linkage. lower the pressure in the line increase the pull on the brakes.

this system is fail safe being self contained at each car, this system works best with out the aid of safety chains as long as function gladhands are in use.
I can post pictures of the setup on my fire car is you like

I can answer more questions in the morning
Night all

[Harold_V]

because the of volume difference created be the piston rod,

More likely because of the decreased surface area (the area of the rod). Volume shouldn't play a role in this particular application, as it's the pressure *per square inch* that is relevant.

Harold

[RCW]

well, its late but i can get started with the following,

...

I can post pictures of the setup on my fire car is you like

I can answer more questions in the morning
Night all

Please do! Any drawings?

Thanks for your original post and for this one!

[cbrew]

because the of volume difference created be the piston rod,

More likely because of the decreased surface area (the area of the rod). Volume shouldn't play a role in this particular application, as it's the pressure *per square inch* that is relevant.

Harold

This is correct
I did say it was late

[cbrew]

ok I feel much better after a good nights sleep,
I will add to my earlier description,
there is a quick release valve at the cylinder that vents the air from the cylinder directly at each car, this greatly speeds up the reaction time when the condition
here are the pictures requested warrants it (aka emergency application)

[FLSTEAM]

I think this is what you are looking for. When the train line is charged, 70 psi, the pressure on the left side is greater due to two factors. First there is a pressure loss thru the check valve determined by the crack pressure. Second as pointed out above the surface area of the right side is smaller. When the train line sees a pressure reduction the air in the tank applies the brakes. In theory a 10 lb. drop in the train line will cause a 10 lb. pressure to be applied to the brakes. The size of the air tank will determine the max pressure that can be applied. Just for this example lets say the max pressure could be 35 lbs.