Spring Brake

Basic Functions Of Trailer Spring Brake Valves

Spring brake valves are designed for three primary functions:
1. To fill the reservoirs
2. To release the spring brake side of the brake chamber.
3. Engage the spring brakes for parking and during emergency situations such as breakaway. A more detailed description can be found in the Tech section About subsection.

This is a simplified description and does not take into account service brake operations, specific model features, or additional built in protections.

The spring side of a brake chamber will release the brakes when ample air pressure is supplied. This is opposite of the service side of the chamber.
The supply port on the valve is connected to an air line from the red gladhand. When air pressure is introduced it begins to fill the spring brake chambers through the delivery ports. Eventually the pressure builds until it cages (retracts) the spring allowing the trailer to move. The reservoir(s) are filled at the same time or after the spring brakes have been released dependent upon valve design.

When the pressure is removed the valve exhausts the air from the spring side of the chambers. This locks the brakes. The air that is in the reservoir is trapped by a check valve.

Compounding is a situation where both the service and spring sides of a brake chamber are engaged in applying the brakes. This can be very hard on brake parts.

The 'Control' port should be connected to the control (blue) line of the brake system. This is designed to prevent compounding of the brakes by venting (disabling) this line is when the spring brakes are engaged.

Spring Brake Technical