GILLIG LOW FLOOR, Руководство по обслуживанию

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Hydraulic System
306
FAN MOTOR CIRCUIT VALVES
Spool Valve
The spool valve is a pilot operated bypass relief valve that attaches to the fan motor. It is fully closed
when the engine is hot and fully open when the engine is cold. The control spool moves gradually from
the fully closed position to the fully open position as an effect of pilot flow routed through the spool
orifice (see Figure 8- 3 ). The higher the pilot flow the higher the pressure drop across the spool, causing a
greater net force to compress the spool spring and opening the spool.
There are two additional components within the switching valve housing. They are (1) the pressure sen-
sitive pilot valve and (2) the anti-cavitation check valve.
The pressure sensitive pilot valve is used to limit the maximum speed of the fan. It opens at a predeter-
mined pressure level and creates a flow path through the control spool orifice. This causes the control
spool to partially open and limit maximum system pressure and, therefore, maximum fan speed.
The anti-cavitation check valve prevents cavitation that could occur when the fan overruns or windmills
in the vehicle air stream.
As a system, the spool valve and the control or thermostatic valve are open when the engine coolant
is below 194° F. This allows the oil to bypass the fan motor, causing the fan to idle. As the coolant get
hotter, both valves progressively close, causing the fan motor speed to increase gradually proportional to
temperature increase.
Spool Valve Repair
1. Thoroughly clean the exterior of the spool valve/fan motor assembly taking care to block all
ports to prevent dirt from entering.
2. Remove all port adapters.
3. Remove the valve from the motor as follows:
a. Remove the three socket capscrews securing the valve to the motor pressure port. Be careful
not to drop the screw and spring washer to the inlet port inside the valve.
b. Gently pull the valve off the motor.
4. Because the spool valve and motor are attached, cleaning the relief valves and changing the seals
are the only repairs which may be undertaken on the spool valve/fan motor unit. Replace the
seals as follows.
a. Remove the Allen screw and the pilot return union securing the cap to the valve body.
b. Discard the two O-rings in the cap together with the bonded washer on the pilot return.
c. Thoroughly clean the cap.
d. Replace the two O-rings using a little light grease to retain.
e. Carefully replace the cap, pilot return union, bonded washer, and socket cap screw.
f. Apply Locktite #242 on screw threads and torque to 21 ft-lb (28 N-m).