PREVOST LE MIRAGE XLII BUS SHELLS, Maintenance Manual

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PP-1 PP-5
RD-3
SD-03-361
1*
PUSH-PULL TYPE CONTROL VALVES: PP-1, PP-2, PP-5, PP-8, & RD-3
FIGURE 1 - PUSH-PULL TYPE CONTROL VALVES
*FORMERLY SD-03-61
PP-2
PP-8
DESCRIPTION
The PP valves are push-pull manually operable on-off air
control valves with an exhaust function. Most are pressure
sensitive, so that they will automatically move from the ap-
plied to the exhaust position as supply pressure is reduced
to a certain minimum, depending on the spring installed.
The exception to this is the PP-8 valve and some PP-1 valves
which have no spring. The PP-8 valve also has a larger di-
ameter shaft for button mounting so that when installed on
the same panel with other PP valves the buttons cannot be
inadvertently mixed. The PP-8 is normally used to operate
tractor spring brakes independently from the trailer.
The PP-5 is unique in having an auxiliary piston in the lower
cover which, upon receiving a pneumatic signal of 18 psi or
more, will cause the valve to move from the applied to the
exhaust position from a 100 psi application.
The RD-3 differs slightly in that it normally remains in the
exhaust position and requires a constant manual force to
hold it in the applied position.
The PP-2 has an auxiliary port which may be plumbed into
a service brake line to release the spring brakes if a service
application is made, preventing compounding of forces on
the foundation brakes.
PREVENTIVE MAINTENANCE
Every six months, 50,000 miles or 1800 operating hours,
disassemble, clean and replace parts if necessary.
REMOVAL
Block and/or hold the vehicle by a means other than air
brakes and drain all reservoirs.
1. Drive the Button Roll-Pin out with a punch and remove
the button.
2. Mark each air supply line and its port for easy reinstalla-
tion, then disconnect them. Remove the valve from the
panel by removing the Panel Mounting Nut.