51
4.12
F
ITTING AND ADJUSTING THE
HWM
MECHANICAL ACTUATOR
Ensure that the thread of the HWM mechanical actuator being used is the same type of
thread as the existing adjustment bolt on the PRV pilot valve.
(HWM can supply alternative threads if the actuator is unsuitable).
Screw the top nut and bottom nut
towards the middle nut so that they
are together (see picture).
Screw the actuator thread into the
actuator head until it is finger tight.
(Use the middle nut).
This moves the plunger to the top of
the inside of the actuator upper
chamber. The pin (lower part of the
plunger) should now be fixed.
Note the depth into the pilot valve
of the existing bolt. Also note the
force required to turn it at that
position.
Unscrew and remove the existing PRV pilot adjustment bolt.
(see picture). Check the outlet pressure reading whilst removing the
bolt; the pressure should not change. If pressure drops at this point a
valve is leaking.
Note: Use a pressure gauge on the PRV outlet side.
Screw the HWM mechanical actuator into the pilot of the
PRV.
It should be positioned at approximately the same depth
as the pilot bolt, which has just been removed.
Rotate the actuator to apply the same force that was
applied by the (now removed) adjustment bolt.
Open both the input and output path of the pilot valve
together (at the same time, if closed).
This will permit water to flow through the pilot valve; its
diaphragm is no longer hydraulically locked in position.
Slowly open the PRV top chamber valve. The PRV will
now return to pilot control, influenced by the actuator
pin position.
Thread
Bottom Nut
Middle Nut
(fixed location)
Head
Top Nut
(Pin)
Old
bolt
