150-712-200-02
Appendix A - Technical Reference
HRE-712 List 1 and List 2
July 26, 2000
37
Replacing the Pressure-Cutoff Valve
The Pressure-Cutoff Valve (PCV) is part of an all-metal, nickel plated brass assembly, as shown in
. The valve controls the flow of air from the air core stub (air-filled unit) or the external air inlet
valve (gel-filled unit) into the enclosure.
The assembly consists of an adjusting knob with stem that is interlocked to a limiting nut. The outer limiting nut
screws into the outer threads of the body housing connected to the enclosure’s baseplate. The stem screws into the
inner threads of the housing. The stem tip has thread O-rings that open and close the air flow through the base of
the body housing.
When the adjusting nut is fully clockwise, the air flow is OFF. When it is rotated one turn clockwise, the airflow
is ON. The body housing also has a thread O-ring to create an airtight seal when the limiting nut is tight.
To remove and replace the PCV:
1
Loosen the limiting nut with a 1-inch (2.54 cm) wrench by turning it one-half turn counterclockwise.
2
Since the valve stem is internally threaded to the body housing, both the limiting nut and adjustment knob
must next be turned together. Turn them counterclockwise until both are fully unthreaded from the body
housing.
3
Pull the adjusting knob and limiting nut subassembly away from the body housing until completely
disengaged. Some resistance will occur as the stem’s O-rings rub against the walls of the body housing.
4
Check that the O-ring remains attached to the threaded tip of the body housing.
5
The replacement PCV assembly comes as a unit, which includes the limiting nut, adjustment knob, and all
O-rings. Do not attempt to disassemble it.
Insert the valve stem into the body housing’s threaded tip as far as possible. Some resistance will occur as the
O-rings contact the inner housing threads.
6
Rotate the limiting nut one-half turn clockwise.
7
Grasp both the limiting nut and adjustment knob and tighten this subassembly into the housing until the
adjusting nut tightens the O-ring against the body housing. Do not crossthread.
8
Turn the adjusting knob clockwise until contact is felt between the stem’s O-rings and the inner threads of the
body housing.
9
Use the 1-inch (2.54 cm) wrench to torque the limiting nut to 200 inch-pounds. Do not overtighten. Excessive
torque does not improve the seal and may damage the PCV.
10
Check that the adjusting knob has at least 1
1
/
2
turns of free movement in and out.
11
If any binding occurs, loosen the limiting nut and turn the adjustment knob until it moves freely. Retighten
the limiting nut.
12
Rotate the adjustment knob a full turn counterclockwise from its full clockwise position. This should turn the
pressure ON.
13
Pressurize the chamber and check the entire assembly for leaks.
14
Rotate the adjustment knob back and forth and determine that it does turn the airflow OFF when fully
clockwise and ON when backed off one turn counterclockwise.
