Dual-piston relay valve having an anti-compounding function

A method of operating a relay valve for a vehicle, the relay valve comprising:

• a housing including a first housing part and a second housing part provided separately from the first housing part;
• a parking brake piston that is displaceable axially in the first housing part;
• an axially displaceable cuff;
• a first compressed air chamber for receiving compressed air from a control line formed between the parking brake piston and the first housing part;
• a first spring element, which loads the cuff axially with a preloading force;
• a second spring element, which loads the parking brake piston axially with a further preloading force, wherein the second spring element comes into contact with a spring plate arranged in the second housing part;
• and
• an axially displaceable service brake piston in the second housing part of the housing arranged axially between the parking brake piston and the cuff, said service brake piston coming into contact at least radially against the parking brake piston and radially against the housing in a sealing manner, in order to form a second compressed air chamber, wherein
• the second compressed air chamber is fed directly with compressed air from a service brake line, which is arranged on a service brake, and
• a third compressed air chamber sets the air pressure in an output line connected via a venting connection is formed between the service brake piston, the housing and the cuff,
• the method comprising the acts of:
• when the vehicle is parked, depressurizing the control line, the service brake line and the output line, wherein
• the cuff comes axially into contact with a housing-side valve seat and the service brake piston is spaced axially apart from the cuff, whereby the third compressed air chamber is vented via a pneumatic outlet formed axially between a valve seat formed on the service brake piston and the cuff.