F-1031, Section 2119
Page 21 of 24
Air Inlet Valve Function
The air inlet valve is part of the control air circuit and con-
trols the incoming air to the compressor by opening and
closing. The air inlet valve operates (or follows) based on
the air signal it received from the fixed regulator, the bal-
ance valve or minimum pressure valve.
The figures below show the air inlet valve in an open and
closed position. Let’s see how and why the valve open
and closes.
When the compressor is running, there is negative air
pressure behind the main valve disk, and if only a small air
control pressure is on the valve’s control disk, the air inlet
valve opens. As long as the control air pressure is low, in-
let valve remains open. With the air inlet valve open, the
compressor will pull in more air resulting in more pressure
and/or flow at the compressor discharge.
To stop the compressor pressure increase or restrict the
compressor air flow, the air inlet valve needs to close. The
air inlet valve will close when the control air pressure at
the valve’s control disk is high enough to overcome the in-
let pressure on the main valve disk. With the air inlet valve
closed, no more air can be pulled into the compressor.
The discharge pressure of the compressor stabilizes and
air flow stops.
In operation, the air inlet valve is constantly opening and
closing (or modulating) to maintain the desired pressure
called for by the control air mechanism (fixed air regulator,
piloted balance valve, or minimum pressure valve). It
should also be noted the air inlet valve has an air inlet trim
valve (AIVT) with an air bleed off outlet. This provides a
means to bleed off control air continuously and at a con-
trolled rate. The AITV is used to calibrate the air control
system.
Air Inlet Valve - Closed
Air Inlet Valve - Open
AITV
Air Bleed
Off Outlet
AITV
To
Compressor
