1
®
SD-03-3619
Bendix
®
PP-DC
™
Park Control Valve
FIGURE 1 - PP-DC
™
PARK CONTROL VALVE
SUPPLY 12
EXHAUST
SUPPLY 11
BUTTON
EXHAUST
SUPPLY 11
BUTTON
COVER
DELIVERY
21
DESCRIPTION
The Bendix
®
PP-DC
™
park control valve is a push-pull,
manually operable on/off valve. It is dash board-mounted
and provides in-cab control of truck or bus parking brakes.
The valve is pressure sensitive – it automatically moves from
the applied to the exhaust position if total system pressure
drops below 20 to 30 psi. Also, manually pulling the button
will apply the parking brakes.
The PP-DC
™
valve body is made of non-metallic, non-
corrosive material, and the cover is available in two mounting
variations (see Figure 1). The valve is designed to accept
1/4" P.T. fittings or push-to-connect fittings that use SAE
J844D non-metallic air brake tubing.
Ports:
Port
Embossed I.D.
Primary Reservoir Supply
Supply 11
Secondary Reservoir Supply
Supply 12
Delivery
Delivery 21
Exhaust
Exhaust 3
Operating pressure: 150 psi max.
Operating temperature: -40° to 200°F
Basic valve weight: Approximately .8 lbs.
OPERATION
GENERAL
The PP-DC
™
valve receives its supply of air from the primary
service reservoir or the secondary service reservoir, whichever
is at the higher pressure. When the button is pushed in, the
valve delivers air to the spring brake chambers (usually
through a spring brake valve such as the Bendix
®
SR-1
™
valve and a relay or quick release valve). The air releases
the spring brakes for normal vehicle operation.
To apply the parking brakes, the button is pulled out, which
exhausts the PP-DC
™
valve delivery and releases air from
the spring brake chambers.
If total system pressure drops below 20 to 30 psi, the valve
will automatically “pop out,” which removes the hold-off air
in the chambers and applies the spring brakes.
PARKING BRAKES RELEASED
To release the parking brakes, the push-pull button is pushed
in. The PP-DC
™
valve plunger moves, closing the exhaust
port with the exhaust seal and allowing the plunger o-ring to
move past the guide spool. Supply air then travels out the
delivery port to release the brakes.
Note that Figure 3 shows the primary service reservoir
supplying the PP-DC
™
valve. The double check valve
diaphragm has sealed the secondary reservoir supply port
and allows air to pass from the primary reservoir into the
PP-DC
™
valve.
