Components of the spring-brake trailer air system (Fig. 49) are:
- front-service reservoir
- rear-service reservoir
- trailer spring-brake valve
- relay valve (same as on tractor - not an emergency relay valve as used on trailers)
- spring-brake chambers
The new component - the trailer spring-brake valve (Fig. 50) - is responsible for several important functions:
- It controls application and release of the trailer’s spring brakes.
- It protects and isolates the front-service reservoir from the rear-service reservoir. This is an important feature that prevents an automatic application of the spring-brakes, even though the trailer’s service reservoir is lost.
- It prevents automatic spring-brake application if the trailer’s supply line has a gradual leak.
- It will automatically apply the spring brakes if supply pressure is rapidly lost (after a breakaway).
- Drivers can check the operation of the trailer spring-brake valve by closing the supply valve on the tractor or by disconnecting the supply line between the tractor and trailer with the supply valve in the open position.