Air brakes
Balanced
Balanced air brakes rely on dual-acting cylinders to apply and release the brakes. A single air line from the locomotive brake valve controls the operation of the brakes.
Balanced air brakes are also referred to as "Automatic Air Brakes", because a break in the air line (i.e. part of the train becomes uncouple and pulls the glad hands apart) will cause all brakes to apply on both segments of the train. This operation is in accordance with prototype air brake systems.
Push to Apply
According to Harry Haas, the Push to Apply Automatic Air Brake was designed by Jim Murray. Harry describes the system as follows:
- The AAB circuit is designed to operate at 40 PSI. The air cylinders used have a bore of 1-1/16 inch. The bore depends on the type mechanical setup used on the trucks.
- The air reservoir for each car should be as large as possible. I use 2 inch by 10 inch PVC pipe (schedule 40).
- The control system is from the locomotive cab. A plunger type air pressure regulator (Clippard MAR-1C) under the cab, activated by a cam setup with an air brake stand above the floor. One for the independent air brakes or steam brakes on the locomotive (engine and tender) and one for the automatic air brakes on the train.
- The air switch (Clippard TV-3S) allows the brakes on each car to be individually released without voiding all the air in the reservoir (e.g. to take the car out of the system and remain within the train). Also, a car may be set out on a siding and the brakes released.
Pull to Apply
Clippard Parts
Serveral current air brake designs use Clippard parts. They have been reported to work well, are virtually leak free, and Clippard's website is easy to navigate for ordering low-volume parts. Here is a list of commonly used parts.
- SDR-17-1 : Stainless steel double-active cylinder, 1 inch stroke, 1-1/16 inch bore
- MAR-1C : Plunger-type pressure regulator, 10-100 PSI
- 11752-4 : #10-32 to 1/8 inch barb fitting
- T44-4 : Tee fitting, 1/8 inch ID
- URH1-0804-BKS : Urethane tube 1/8 inch ID
- 11924-1-ENP : 1/8 inch Pipe to 1/8 inch hose fitting
- TV-3SP : 3-Way Toggle Valve, ENP Steel Toggle, 1/8" NPT
- MCV-2 : Check Valve, #10-32 Ports
Non-equalized
External References
- Gerry Stuteville's "Auto Air Brakes"
- "Affordable Air Brakes by Harry Haas"
- "Real Brakes for Model Railroaders"
- "Cup Seal Vacuum Motor", Lee Nonnemacher, Pennsylvania Live Steamers
- "Air brake question", Chaski.org
- "Air brakes", Chaski.org
- "Freight Car Brake Rigging Arrangements", Wabtec Corp (PDF)
- "Wabtec Freight Catalog" (PDF)