Hale MG - Manual (Page 84)

Muscle Pumps
5-20
G. Relief Valve Systems
1. PM/PMD Control Valve
(Refer to figure 6-14)
a. Park the vehicle on a level surface.
Shut down the engine. Set the parking
brake and chock the front and rear
tires.
b. Drain the fire pump. Tag and
disconnect wires to indicator light.
c. Rotate the adjustment handwheel
counterclockwise to remove the
spring tension.
d. Remove the cap screw and nut
attaching the adjustment handwheel to
the adjustment shaft. Then, remove
the handwheel.
IDENTIFY AND MARK THE LINE
CONNECTIONS ON THE CONTROL BODY
BEFORE REMOVING. IMPROPER CONNECTION
OF LINES MAY RESULT IN THE FAILURE OF
THE PILOT VALVE, WHICH COULD CAUSE
DAMAGE TO THE FIRE PUMP.
e. Remove the pump discharge pressure
line and the relief valve line from the
control body of the pilot valve.
f. While holding the pilot valve, remove
the four 1/4-20UNC X5/8 inch long
machine screws attaching the valve
and cover plate to the Pump
Operator’s Panel, and separate the
valve, plate, and the relief valve
setting indicator (if equipped with
PMD) from the panel.
g. Disassemble the Control Valve.
1) Remove the four 5/16-18UNC X
1 inch long allen-head cap screws
securing the control body to the
rear of the spring housing. Then,
remove the control body.
DO NOT USE PLIERS TO UNSCREW THE
CONTROL VALVE FROM THE DIAPHRAGM
CLAMP. DAMAGE TO THE CONTROL
VALVE WILL RENDER THE PILOT VALVE
INOPERATIVE.
2) Unscrew the control valve from
the diaphragm clamp. Remove
the diaphragm washer and the
diaphragm.
3) Remove the retaining ring, the
seal and the bearing.
USE A SPRING COMPRESSOR TO
REMOVE THE CONTROL SPRING. THE
SPRING IS UNDER COMPRESSION, AND
COULD BECOME UNCOMPRESSED, WHICH
COULD RESULT IN PERSONNEL INJURY.
4) Turn the adjustment handwheel
clockwise to unscrew the adjust-
ment shaft from the adjustment
nut. From the handwheel end,
remove the adjustment shaft from
the spring housing.
5) Remove springs, the adjustment
nut, and diaphragm clamp as an
assembly from the spring housing,
and then separate.
h. Clean all the control components.
Inspect and lubr icate with grease the
threads on the adjustment shaft.
i. Assemble the control valve.