Air Brake Question

[realtrains]

Phil McFadin will be missed by all that knew him and many he helped. His site "realbrakes" was an outgrowth of his work here at real trains. I have a lot of his work and patterns for parts he developed and will help to answer questions about brakes.

Bill Donovan
Real Trains, Inc.

[Fender]

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 warrants it (aka emergency application)

Chris, first of all I want to thank you for posting all this information on air brakes. I have struggled to understand how to build such a system using commercially-available parts, and you have explained this very well.
One thing I don't understand though, is about the quick release valve. As I understand it, this valve opens if the pressure in the train line drops by more than a certain amount (5 psi if I understand the part description). Does this mean that any "service" brake applications must be less than 5 psi, otherwise the brakes go into emergency?
Thanks,

[cbrew]

those quick release valve from clippard will open at even the slightest pressure difference and will re close once the pressure equal out again.
I confirmed this when connected a tube to the exhaust port and put the other end in a cup of water.

does it do it all the time.. who knows. but what i do know is they will open ever time i do a rapid drop in the train line (aka emergency )

thinking back on operations,

even when i had ten cars in the train with all the "braked" cars going all the way back to the engine of the train, it did not slow down the time it takes to make a 5 or 10 psi reduction. so that is telling me the valves are doing there jobs ever time.

in real life. it takes a 5 psi reduction to set the brakes and another 5psi to start creating usable drag and another 5psi if the train is extra heavy or on a steep decent. so them opening with a slight reduction does not come into play.

even with all this, a full on emergency application still processes a smooth, controlled stop

I dont know if i already shared these pictures of my latest build or not. but here they are again

this is what everyone sees

you will find the quick release valve at the end of the air cylinder

this is the business end of the system

[Fender]

OK, now I understand. The exhaust valve "senses" the pressure difference between the train line and the cylinder. If the train line pressure is lower, then the valve vents air from the cylinder to atmosphere, until the cylinder and train line pressure is equal. Then, the valve stops venting. Thanks,

[Steamin]

Appreciate all the information in this thread. I've got a pretty good idea of what's on the cars, what kind of valve do you use up in the cab to apply/hold/release the brakes? I saw one mention of a proportional valve....

Steamin

[cbrew]

here is the cab shot as i was assembling the ten wheeler. both engine and train brake valves have service, lap, release and emergency.

[Erskine Tramway]

Hi Folks. New guy here. These are the brake valves I designed and built for 15" gauge equipment when I worked at the Sandley Light Railway Equipment Works, Inc., during the 1960's and '70's. This set is on the engine I ran most of the time, Atlantic #128, and a second picture of the unfinished set that Norm Sandley gave me when I left to hire out on the BN in 1977. We had full #6-ET equipment on the engines and triple valves on the cars. The brake pipe we carried was 40psi
with a 60psi "main drum", and a 10 pound reduction would make a 'planned' stop with a passenger train. The Triple valves were Williams Air Brake #WM-198 "Proportional Trailer Breakaway Valves". They are no longer made, but their successors make a similar valve, which can be used. They are larger than "scale", but I think that the "guts" could be adapted to fit inside a 2-1/2" scale "K" or "P" Triple body casting. For more modern equipment, the diaphragm would "hide" pretty well inside an ABDW Control valve casting.

Enjoy,

Mike Decker