TM 3-1040-26334
CHAPTER 2
FUNCTIONING OF EQUIPMENT
Section I. PNEUMATIC SYSTEM
the second stage is forced down into the cylinder bore
2-1.
General
until the plunger shoe contacts a flat on the compressor
keystone, forcing the plunger to follow the keystone flat.
This section describes the pneumatic system functioning
The position of the keystone flat follows the eccentric on
of the AN-M4D compressor.
the compressor crankshaft in a cyclical manner, causing
the second-stage plunger to travel in a reciprocating
2-2.
Functional Description
fashion within the cylinder bore. During the intake
stroke, compressed air forces the plunger downward
The AN-M4D compressor pneumatic system provides
until the cylinder cavity pressure equals atmospheric
dry, 2, 000 psi compressed air at a flow rate of 3.5 cfm.
pressure, allowing the spring-loaded inlet valve to seat.
To develop this air pressure, the air compressor is
On the compression stroke, the air is further compressed
operated at a maximum speed of 3, 600 rpm by a military
by the second stage plunger until the pressure
standard engine.
differential between the second stage and the third stage
unseats the second-stage discharge valve. The open
a
First Stage.
When the compressor is
discharge valve permits the compressed air to flow to the
operated, the first-stage piston, attached to the
next compression stage.
crankshaft keystone assembly, is forced to travel in a
reciprocating manner within the first-stage cylinder (fig.
c. Third Stage. This operational procedure
2-1). During the downward (suction) stroke, the piston
continues in the third stage until the compressed air in
creates a pressure differential between atmospheric
the pneumatic system downstream of the compressor
pressure and internal cylinder pressure. This pressure
reaches the operational pressure of 2, 000 psi.
differential forces the first-stage inlet valve to unseat and
the outlet valve to seat more firmly. With the inlet valve
d. Heat Exchangers and Aftercooler. The
unseated, the first-stage inlet passage is open, drawing
compressed airflow from the first stage to the second
atmospheric air through a 40-micron inlet filter, past an
stage and from the second stage to the third stage
inlet valve to fill the first-stage cylinder, eliminating the
passes through heat exchangers. From the third stage,
pressure differential. After traveling the full downward
the compressed airflow is directed through the third
stroke, the first-stage piston is forced in the opposite,
stage heat exchanger to an aftercooler and water
upward direction. Since atmospheric pressure and first-
separator with a pressure relief valve.
stage cylinder pressure are equal, a pressure increase
during the compression stroke seats the inlet valve,
e. Water Separator.
From the water
preventing passage of the cylinder air to the atmosphere.
separator, the compressed airflow is directed to the
During the compression stroke, the piston further
water separator outlet plug and then to the using
compresses and consequently decreases the air volume,
equipment. The hot, high-pressure compressed air,
causing an increase in cylinder air pressure and
when passing through the finned heat exchangers and
temperature. The increased first-stage air pressure
aftercooler, radiates the heat of compression to the
forces open an outlet (discharge) valve.
The
ambient air. To increase the heat transfer rate, a
compressed air from the first-stage discharge valve is
compressor fan forces ambient air past the finned cooler
directed to the inlet port of the second-stage inlet valve.
surfaces. With the increase in pressure and loss of
compression heat, moisture is condensed and squeezed
b. Second Stage. Again, due to pressure
out of the compressed
differential, the second-stage inlet valve is unseated,
permitting the compressed air to flow into the second-
stage cylinder. A free floating plunger in
2-1
