Bendix Commercial Vehicle Systems PP-7 TRAILER SUPPLY VALVE - Manual (Page 3)

3
after it is depressed and it will remain in until supply air
pressure falls below 40 P.S.I. or until the valve is manually
actuated.
OPERATION - LESS THAN 50 P.S.I. SYSTEM
PRESSURE
With less than 50 P.S.I. system air pressure, the button of
the PP-7
™ valve will be out and the park control valve will not
deliver air to the control port of the PP-7 ™ valve. In this
condition supply air cannot flow past the closed plunger inlet
and the plunger exhaust valve is off its seat. With no air
pressure on the control port, the control inlet is seated and
the exhaust passage through the control piston is open.
OPERATION - ABOVE 50 P.S.I. SYSTEM AIR
PRESSURE
When system air pressure is greater than 50 P.S.I., the button
of the PP-7
™ valve can be depressed and will stay in. If the
vehicle is in the running condition, the park control valve will
be delivering system air pressure to the control port of the
PP-7
™ valve. (See Note.)
With the button of the PP-7 ™ valve depressed, the plunger
inlet will be open and the exhaust valve will be seated, sealing
the exhaust vent. Supply air is permitted to flow through the
body to the control inlet and exhaust valve. With the park
control valve delivering full system pressure to the control
port of the PP-7
™ valve, the control piston moves into contact
with the control valve, closing the exhaust passage through
the piston and opening the inlet. Opening the control inlet
permits supply air to flow out the delivery port of the PP-7
™
valve. (See Note.)
NOTE: If the vehicle is parked and system air pressure is
above 50 P.S.I., the park control valve will not be
delivering air to the PP-7
™ valve control port and the
control inlet valve will be closed. In this case no air
will be flowing from the delivery port of the PP-7
™
valve.
OPERATION - MANUAL OR AUTOMATIC
EMERGENCY
MANUAL
In order to disconnect the tractor and trailer, the button of
the PP-7
™ valve is pulled by the operator. Pulling the button
closes the plunger inlet and unseats the exhaust valve. Air
that was flowing out the delivery port returns to the PP-7
™
valve and is exhausted from the vent in the midsection of the
PP-7
™ valve.
NOTE: If the parking brakes were applied prior to pulling
the PP-7 ™ valve button, no delivery air would be
present to exhaust. Delivery air would have been
exhausted when the parking brakes were applied.
See “Operation Park Application.”
AUTOMATIC
In the event of trailer breakaway or a sudden complete failure
of the trailer supply line, the button of the PP-7
™ valve will
pop out when air pressure in the supply line falls below 40
P.S.I.
FIGURE 5 - PP-7 ™ TRAILER SUPPLY VALVE SYSTEM FULLY CHARGED
PP-7 ™ VALVE SYSTEM FULLY CHARGED
#1 Service
Reservoir
#2 Service
Reservoir
Double
Check
Valve
Park
Control
Valve
To
Parking
Brakes
Supply
Port
Plunger
Inlet & Exhaust
Exhaust Vent
Control Inlet
and Exhaust
Exhaust
Port
Control
Piston
To Tractor
Protection
Control Port