TM 5-4940-228-14
CHAPTER 9
REPAIR OF COMPRESSOR
9-1. General.
The air compressor is a four cylinder recip-
rocating type with a capacity of 80 psi to 15 cfm.
Reed type valves with unloaders are used to allow
for continuous operation. Unloaders are controlled
by the unloader pilot valve which maintains a pres-
sure range of 65 psi to 80 psi in the pulsation
chamber.
9-2. Operation.
Consider a piston at the top of stroke and begin-
ning to go down into the cylinder. As the piston is
pulled downward by crankshaft rotation, a vacuum
is formed in the cylinder allowing atmospheric pres-
sure to force the intake valves open. Air is drawn
through the filter, past the intake valves and into
the cylinder. Discharge valves are held closed by air
pressure in the pulsation chamber. When the piston
starts its upward stroke, pressure in the cylinder ex-
ceeds intake air pressure, forcing intake valves
closed. As the piston continues upward air is com-
Key to Figure 9-1:
1. Pipe
2. Drain cock
3. Bolt (4)
4. Pulsation chamber
5. Screw (6)
6. Filter retainer (2)
7. Outer filter (2)
8. Inner filter (2)
9. Screen (2)
10. Bolt, long (4)
11. Lock washer (2)
12. Unloader (2)
13. Bolt, short (8)
14. O-Ring (2)
15. Head (2)
16. Gasket (2)
17. Valve assembly (2)
18. Gasket (2)
19. Nut (12)
20. Lock washer (12)
21. Cylinder (2)
22. Gasket (2)
23. Lock wire (8)
24. Bolt (8)
25. Piston (4)
26. Nut (2)
pressed and increases in pressure until it exceeds
pulsation chamber pressure. The discharge valve is
forced open, allowing cylinder air to enter the pul-
sation chamber until the piston reaches top of
stroke. As the piston starts down, cylinder pressure
becomes less than pulsation chamber pressure
which closes the discharge valves and the process is
repeated. Unloading occurs when pressure from un-
loader pilot valves forces unloader pistons down
against the intake valves. Since intake valves are
now open continuously, cylinder pressure cannot
build up enough to open valves. No air is pumped
into the pulsation chamber. Internal lubrication is
automatic by splash from dippers on the connecting
rods. Intake air filters and silencers are pad type at-
tached directly to the cylinder head. Air cooling is
by fins cast into cylinders and heads, also, pulley
has cast blades which force air over fins
9-3. Disassembly.
Use Figures 9-1, 9-2, 9-3, and 9-4 as guides and
proceed as follows:
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
Bolt (2)
Pulley
Key
Breather cap (2)
Spring (2)
Valve (2)
Seat (2)
Pipe plug
Coupling
Nipple
Street elbow
Dipstick
O-Ring
Bolt (5)
Rear, carrier
Gasket
Oil seat
Bolt (5)
Front, carrier
Gasket
Bearing cup (2)
Bearing cone (2)
Crankshaft
Stud (12)
Crankcase
9-1
