Air Brake Manual

This content makes me feel
Google Translate is a third-party tool, and is not owned or administered by SGI. SGI is not responsible for any errors or omissions as a result of the translation. In case of a difference in interpretation between the translated version and the laws and regulations governing Saskatchewan drivers and vehicles, the laws and regulations prevail.

Spring-brake trailer system

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
Trailer equipped with spring brakes
Figure 49. Trailer equipped with spring brakes


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).
  • You 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.
Trailer spring-brake valve
Figure 50. Trailer spring-brake valve


Rev: 2018