Troubleshooting guide

31
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Park Control Valves
The Bendix
®
PP-DC
®
park control double check
valve is a push-pull, manually operable on/off valve
with an integral double check. It is dashboard mounted
and provides in-cab control of truck or bus parking
brakes. Manually pushing or pulling the button will
release or apply the parking brakes. The integral double
check valve allows the PP-DC valve to receive supply
air pressure from either, or both, the front or rear axle
service reservoirs.
Section 4: Tractor Parking, Trailer Charging/
Parking and Emergency Systems
The tractor/trailer parking and emergency system
typically consists of:
• The tractor parking control system;
• The trailer parking and emergency system; and
• The tractor protection system.
See section 12 for system schematics.
Tractor/Trailer Parking and Emergency Systems
Service
Relay
Valve
Bendix
®
PP-DC
®
Park Control Valve
Bendix
®
SR-7
®
Spring Brake
Modulating
Valve
The valve is pressure sensitive and automatically moves
from the applied (over-the-road position) to the exhaust
position (thus applying the parking brakes) if total system
pressure (both front and rear axle reservoirs) drops
below 20 to 30 psi.
(See the full system schematic in
section 12 for more details)
Sample Park Control System
PP-DC
®
Park
Control Valve