150-454-111-06
Appendix B - Technical Reference
HRE-454
February 25, 2000
61
Air Stem Valve
The air stem valve (ASV) is part of an all-metal, nickel-plated brass assembly as shown in
is used to pressurize the enclosure from an external air supply or to release the internal pressure. The assembly
consists of an adapter that screws into a brass fitting located in the bottom of the base. The ASV itself screws into
this adapter and the cap screws on to the top of the ASV. The adapter has two O-rings that are required to create
an airtight seal. One is located on its outer threaded stem that connects to the brass fitting. The other is located at
the base of its inner well where it seals the ASV to the adapter.
To remove and replace the ASV, proceed as follows:
1
Grip the adapter nut with a
3
/
4
-inch wrench and the ASV with a
7
/
16
-inch wrench.
2
While holding the adapter nut steady (it should not be moved), loosen the ASV by turning it
counterclockwise, then remove it by hand. If the adapter nut becomes loose, tighten it to a torque of 60 inch-
pounds.
3
Check that the O-ring in the adapter’s inner well has remained in place. If not, reseat it.
4
Thread the new ASV into the adapter. Do not crossthread.
5
Again grip the adapter nut with a
3
/
4
-inch wrench and the PRV with a
7
/
16
-inch wrench and tighten the PRV to
120 inch-pounds of torque.
6
Pressurize the chamber and check the entire assembly for leaks.
Pressure Cutoff Valve
The pressure cutoff valve (PCV) is part of an all metal, nickel-plated 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 inner-locked 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’s tip has three O-rings that work to
open and close the air flow through the base of the body housing. When the adjusting nut is fully clockwise, the
airflow is OFF. When it is rotated one turn clockwise, the airflow is ON. The body housing also has an O-ring on
its threads to create an airtight seal when the limiting nut is tightened down upon it.
To remove and replace the PCV, proceed as follows:
1
Grip the limiting nut with a 1-inch wrench and loosen it by turning 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 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 it is completely
disengaged. Some resistance will be noticed as the stem’s O-rings rub against the walls of the body housing
as the stem is withdrawn.
4
Check that the O-ring remains attached to the threaded tip of the body housing.
Do not overtighten. Excessive torque does not improve the seal and may damage the BVV.
Do not overtighten. Excessive torque does not improve the seal and may damage the ASV.
