SERVICE MANUAL
Fig. 7 Cross Section of Pressure Limiting Valve
1
Piston
5 Piston "O" Ring
2
Valve Guide Wire
6 Exhaust Vent
3
Inlet Valve Spring
7 Pressure Regulating
4
Inlet & Exhaust
Spring
Valve
If pressure in the delivery line exceeds the pressure
setting of the pressure limiting valve, the force exerted by
the air pressure below the piston will be greater than the
spring force above the piston. The piston will move up
from the exhaust valve, permitting air to pass by the
exhaust valve, through the hollow piston and valve guide
and escape through the slot in the adjusting cap. When
the force of the spring above the piston overcomes that
of the air pressure below the piston, the exhaust valve is
seated, and the pressure in the delivery line is the same
as the setting of the pressure reducing valve.
MAINTENANCE
Every 6 months or 80,000 km (50,000 miles). Connect a
test gauge to the delivery line and observe at what
pressure the inlet valves closes, which is the delivery
pressure. If the pressure delivered by the pressure
reducing valve varies more than plus or minus 35 kPa (5
psi) from the pressure setting of the pressure reducing
valve, the valve should be adjusted. The lock nut should
be tightened after each adjustment and lockwire seal
replaced if used. Every year or every 160,000 km
(100,000 miles) perform the SERVICE CHECKS.
SERVICE CHECKS
Operating Check
Connect an accurate test gauge to the delivery line and
observe what pressure the inlet valve opens which is the
delivery pressure. If delivery pressure varies more than
35 kPa (5 psi), adjust the valve to the specified setting.
To raise the delivery pressure the adjusting cap should
be turned clockwise. Tighten locknut after each
adjustment and replace lockwire and seal if used.
Leakage Check
No leakage is permitted at the exhaust vent in the slot of
the adjusting cap when making the operating check.
Leakage at this point would indicate a leaking piston O-
ring or a leaking exhaust valve seat.
If the pressure limiting valve does not function as
described or leakage is excessive, it is recommended
that it be replaced.
REMOVE
Apply parking brakes or block wheels to prevent vehicle
from moving.
Drain service and isolated reservoirs.
Disconnect air lines from the pressure reducing valve.
Loosen valve mounting bolts and remove.
REINSTALL
Check and clean air lines to valve.
Mount valve securely with bolts and lockwashers.
Reconnect lines to the valve.
Disassembly and reassemble of Pressure Limiting Valve
is not recommended as it is serviced as a complete
assembly.
CTS-4079 - CHAPTER III
PRINTED IN UNITED STATES OF AMERICA
Page 7
