Figure 37-8. Suction throttling Valve.
(1) The outlet pressure enters the valve on
gas to flow through the valve and flow to the inlet of the
(2) The gas pressure passes through a fine
As pressure again drops on the inlet side of the valve,
screen and small bleeder holes to act on a diaphragm.
atmospheric pressure and valve spring pressure close
the valve again. A vacuum power unit is mounted to the
(3) The valve spring and atmospheric
top of the valve that helps reduce valve spring pressure,
pressure oppose the gas pressure on the opposite side
preventing icing at high elevations.
of the diaphragm.
d. Pilot-Operated Absolute Suction Throttling
Valve. The Pilot-Operated Absolute (POA) valve (fig.
(4) As the outlet pressure of the evaporator
overcomes the opposing forces, the diaphragm and
37-9) is able to maintain the proper minimum evaporator
piston move upward, allowing low-pressure
pressure regardless of