Government of Alberta Ministry of Transportation:


Glad-hand connectors The glad-hand connectors connect the tractor supply and service lines to the trailer supply and service lines. The supply and service lines must be checked to ensure they are connected correctly. Trailer supply valve The trailer supply valve allows the driver to open and close the service and supply lines. This is a pressure sensitive valve that is mounted on the dash. When activated, it triggers the closing of the service and supply lines to the trailer and applies the trailer parking brakes. Tractor protection valve The tractor protection valve, with the trailer supply valve, prevents excessive air loss from the tractor's service reservoirs if the trailer air system fails. Trailer control valve (hand valve) The trailer control valve is mounted in the cab and applies the trailer's service brakes independently of the tractor service brakes.
The brake chambers
Brake chambers convert the air pressure supplied to them into a mechanical force for applying the vehicle's brakes. The brake chamber consists of two circular metal housings bound by a clamping ring, a rubber diaphragm, a piston, a push rod, and a return spring. Air pressure supplied to the brake chambers from the relay valve acts on the diaphragm to extend the push rod that applies the brakes. When the application pressure is exhausted, the return spring causes the piston and push rod to retract, releasing the brakes.

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