TM 5-4930-218-14
dents. Inspect all threaded fittings for damaged
(1) Remove the screws (1) and high pressure in-
threads.
take manifold (2). Remove spring (4).
(3) Replace all defective parts.
(2) Disassemble the manifold by removing nuts
(5), washer (6), claw (7), washer (8), and nut (9) from
the rod end of the piston (12). Remove the cylinder
and 53) as illustrated in figure 7-1. You should
body (10), gasket (11), piston (12), and packing (13)
tighten manifold cap screws (41 and 52) to a
from the top of the unloader manifold.
maximum of 45 foot-pounds torque.
(3) Remove the screws (22) and remove the low
pressure intake manifold (23). Remove spring (24).
(4) Disassemble the manifold by removing nuts
a. Removal and Disassembly.
(25), washer (26), claw (27), washer (28), and nut (29)
(1) Remove the head unloaders (para 7-3) and the
from the rod end of the piston (31). Remove the cylin-
exhaust manifolds (para 7-4).
der body (30), piston (31), and packing (32) from the
(2) Remove high pressure intake valve (14, fig. 7-
top of the unloader manifold.
c. Cleaning and lnspection.
exhaust valve (44), low pressure exhaust valve (55),
(1) Discard and replace gaskets and preformed
and the related gaskets.
packings.
NOTE
(2) Clean the head unloader parts with dry
When a valve assembly is removed, you should tag it for
cleaning solvent (fed. spec. P-D-680) and dry
identification of cylinder and whether it is an intake or
thoroughly.
exhaust valve.
(3) Inspect all parts for cracks, breaks, wear,
(3) Disassembly of the four valves is similar,
distortion, and other damage. Replace damaged or
Remove screws (16, 35, 46, and 57) and washers (17,
defective parts.
36, 47, and 58). Separate the valve cages (18, 37, 51,
d. Reassembly and Installation.
and 62) and valve seats (21, 40, 48, and 59) and remove
(1) Prior to installation of head unloader in
springs (19, 38, 50, and 61) and valve discs (20, 39, 49,
manifold, you should make sure that the actuating
and 60).
claw is positioned so that it will enter two slots in the
b. Cleaning and Inspection.
compressor intake valve, Refer to figure 7-1 and
(1) Discard and replace all gaskets each time
reassemble the head unloaders in the reverse order of
valves are removed or disassembled.
disassembly. Note the position of the slots in the com-
(2) Clean all remaining parts with dry cleaning
pressor intake valve (14 or 33) and rotate the ac-
solvent (fed. spec. P-D-680) and dry thoroughly.
tuating claw (7 or 27) to corresponding position.
(3) Inspect all valve seats and cages for cracks,
When the head unloader piston (12 or 31) is in up-
breaks, rough or scored seats, and mating surfaces.
permost position, the claw should protrude 1/16 inch
Replace if defective.
below the bottom of the manifold (2 or 23).
(4) Inspect the springs for distortion, weakness,
(2) Holding the piston return spring (4 or 24) in
or broken coils. Replace if defective.
position on the actuating claw with one finger, place
c. Reassembly and Installation.
head unloader manifold in position over compressor
(1) Refer to figure 7-1 and reassemble and install
intake valve. Install screws (1 or 22) drawing up on
the intake and exhaust valves in the reverse order of
both sides a little at a time to insure proper entry of
disassembly and removal. Be sure you replace valve
manifold into compressor valve well. To check for
assembly in the same cylinder from which it was
correct positioning of actuating claw, you should
removed. Do not interchange intake valves and
place a blunt instrument in the opening at the top of
exhaust valves or their parts.
the cylinder body and push down on piston. If correc-
(2) Install the head unloaders (para 7-3).
tly installed, piston will move down and the spring
(3) Install the exhaust manifolds (para 7-4).
wilt return it.
(3) Tighten manifold cap screws (1 or 22) to a
maximum of 45 foot-pounds torque.
a. Description. The centrifugal unloader unloads
discharge lines to prevent compressor action from
starting to compress air until engine speed has in-
a. Removal. Remove the exhaust manifolds (42
creased to a predetermined level, When the com-
and 53, fig. 7-1) by removing screws (41 and 52).
pressor slows down and stops, the discharge line is
b. Cleaning and Inspection.
unloaded through the centrifugal unloader. The unit
(1) Clean all parts with dry cleaning solvent (fed.
incorporates flyweights that control the unloading
spec. P-D-680) and dry thoroughly.
operation as rotational speed decreases.
(2) Inspect the manifolds for cracks, breaks, or
