SUB-SECTION 9C
AIR SYSTEM COMPONENTS
OPERATING AND LEAKAGE TEST. To determine the
3. Connect the air lines to the valve.
serviceability of the exhaust and pressure retaining valve,
perform the following test:
4. Test the valve for serviceability as outlined under the
topic Operating and Leakage Test. Also, check the air line
1. Block the vehicle in position with wheel chocks.
connections for leakage.
2. Fully charge the air system.
EXHAUST & PRESSURE RETAINING VALVE (36Z221)
3. Pull the Maxibrake control knob outward from the dash
DESCRIPTION. The exhaust and pressure retaining valve
panel. The Maxibrakes should release the rear wheel brakes.
performs two important functions. One is to keep the Maxi-
brakes from easing to the applied position due to low air
4. Apply a soap solution to the exhaust port of the valve to
pressure. The other function is to provide a quick local
detect any leakage. Replace the valve if leakage is excessive.
release of air pressure from the Maxibrake chambers when
the Maxibrake control valve is manually or automatically
5. Push the Maxibrake control knob in and note whether or
operated.
not the Maxibrakes set quickly.
When air pressure from the Maxibrake control valve is sup
6. If the valve does not function as just described, or leaks
plied to the inlet port of the valve, the moveable seat is
excessively, it should be replaced or overhauled.
shifted away from the inlet port, closing off the exhaust
port of the valve (see Figure 9C-7). The air pressure must
REMOVAL. To remove the exhaust and pressure retaining
then pass through the drilled passage in the movable seat,
valve, proceed as follows:
pass the check valve, and then out to the Maxibrakes. When
the pressure at the Maxibrakes equals the pressure at the
1. Block the vehicle in position with wheel chocks.
inlet port, the check valve will seat. This will prevent the air
pressure at the Maxbrakes from exhausting through the
2. Open the drain cock on each reservoir to drain the air
inlet or exhaust port of the valve.
system, and depress the Maxibrake control knob to vent
any pressure which may be in the Maxibrakes.
When the air pressure is vented from the inlet port of the
valve, through the Maxibrake control valve, the pressure
3. Disconnect the lines attached to the valve, Then remove
holding the movable seat against the exhaust port seal is
the valve from the machine.
removed. This allows the pressure in the Maxibrakes, acting
on the bottom of the movable seat, to lift the seat. This
opens the exhaust port, allowing the pressure in the Maxi-
OVERHAUL. Overhaul of this valve is limited to the re-
brakes to exhaust through the exhaust port.
placement of the seal, O-ring, gasket, and check valve. To
replace these items, proceed as follows (see Figure 9C-7):
1. Using a suitable wrench, unscrew the lower body from
the housing.
2. Remove the O-ring, seal, gasket, and check valve.
3. Wash all the remaining parts in cleaning solvent.
4. Reassemble the new O-ring, seal, gasket, and check valve
as shown in Figure 9C-7.
INSTALLATION. To install a new or overhauled exhaust
and pressure retaining valve, proceed as follows:
1. Mount the valve on the machine and secure it with
mounting bolts.
Figure 9C-7. Exhaust & Pressure Retaining Valve
(36Z221)
2. Conned the air lines to the valve.
9C-8
