4-65. RELAY VALVE REPLACEMENT.
This Task Covers:
General mechanic's tool kit
Personnel Required: Two (if performing operating test
and leakage test)
Open pressure tank draincock (1) to release pressure in brake system.
Tag and disconnect emergency, service, pressure tank, and airbrake chamber tubes from relay valve (5)
Remove three nuts (2), Iockwashers (3), and screws (4). Remove relay valve (5) from mounting bracket. Discard
Install relay valve (5) on mounting bracket using three screws (4), new Iockwashers (3), and nuts (2).
Apply antiseizing taping to all male threads of tubes.
Connect airbrake chamber, pressure tank, emergency, and service air tubes to relay valve (5). Remove tags.
Close pressure tank draincock (l).
Perform operating test (subpara c).
Perform leakage test (subpara d).
With semitrailer brake system fully charged, check whether brakes apply properly.
Release brakes and check whether air pressure is being exhausted promptly.
With semitrailer brake system fully charged, close shut-off valve in emergency line tube on towing vehicle.
Disconnect towing vehicle emergency air hose from semitrailer air coupling tagged EMERGENCY Check
whether semitrailer brakes apply automatically.
Connect towing vehicle emergency air hose to semitrailer air coupling tagged EMERGENCY Open shut-off
valve on towing vehicle and check that semitrailer brakes release automatically.