1. Install the unloader pilot valve (figure 4, item 5) onto the compressor (figure 4, item 6).
2. Connect the compressed air tubing and fittings from the air tank (figure 4, item 4), the air in from the hydraulic
unloader (figure 4, item 3), and the air out to head unloader (figure 4, item 2) to the air inlet sides of the
unloader pilot valve (figure 4, item 1).
3. Test and adjust the unloader pilot valve as follows:
a. Remove the lockouts and tagouts (FM 55-502).
b. OPEN the applicable COV-COMPR DISCH VALVES CA-1 or CA-2 (figure 1, item 15) and CA-89 or CA-90
(figure1, item 16) and return the air compressor to the normal operation condition (WP 0005 00).
Adjust the pressure switch so that the compressor cutoff pressure is 260 PSI (17.9), as detailed in
Pressure Switch Installation of this work package.
d. With the compressor running and filling the receivers, note the pressure at which the compressors un-
load. Unloading will be signified by a noticeable change in the sound of the compressors accompanied
by a cessation of compressed air delivered to the receivers. The compressors should unload at 250 PSI
e. If the unloading pressure is incorrect, adjust the unloader pilot valve by turning the unload adjustment
screw (figure 4, item 7) clockwise to increase the unloading pressure or counterclockwise to decrease
the unloading pressure.
Drain the air from the starting air receivers by opening valves CA-46 and CA-47 STG AIR TK DR to allow
the air pressure to drop, noting the pressure at which the compressor starts to load. The compressor
should start to load at 210 PSI (14.48 bar). Close the valves when the compressor starts to load.
g. If the loading pressure is incorrect, adjust the differential setting (difference between unloading and
loading pressure) by turning the differential adjustment hex nut (figure 4, item 8). Increase the differential
pressure by turning the hex nut clockwise, and decrease by turning counterclockwise.
h. Adjust the pressure switch so that the compressor's cutoff pressure is 250 PSI (17.2 bar), as detailed in
Pressure Switch Installation in this work package.
Return the equipment to the desired readiness condition.
CHECK PULLEY/SHEAVE ALIGNMENT
1. Place a suitable straightedge (figure 5, item 1) across the compressor sheave (figure 5, item 2) and the motor
pulley (figure 5, item 3). The suitable straightedge should rest firmly across both flanges of the outermost
sheave or pulley.
2. With the suitable straightedge (figure 5, item 1) in place, check for both parallel and angular misalignment
(figure 6). Maximum permissible parallel misalignment is 1/16 inch (1.6 mm). Maximum permissible angular
misalignment is 1/2 degree.
3. If parallel misalignment is found, proceed to step 4. If angular misalignment is found, notify the maintenance