2205Q2JE-HO-S6-N_2020.01.
Chapter 5 Maintenance and Inspection
SCV-series Screw Compressor 5.5 Reassembly
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5.5.12.2 Micro-switches and Micro-switch Cam
The traditional standard unloader indicator uses two micro-switches and one micro-switch cam to
detect the indicated 0 % and 100 % capacity control positions of the unloader slide valve.
If the micro-switch fails or any of these connections becomes loose for some reason, correct position
detection cannot be made, and it causes a problem in the operation control of the compressor.
■ Inspection
a) In the normal condition where the hydraulic line for the capacity control of the compressor is not
opened, set the unloader piston to the no load and full load positions from the manual capacity
control circuit and check the operation of the control circuit to see if the micro-switch can detect the
0 % and 100 % positions of the micro-switch cam (i.e., by checking the operation of the relevant
relays and contacts).
b) After shutting down the control power and carrying out the lock-out and tag-out procedures, remove
the indicator glass and check that the micro-switch mounting screws [126] are not loosened.
c) Check that the hexagon socket head cap screw (set screw) securing the micro-switch cam [127] are
not loosened.
d) After checking that the wiring for the micro-switch has been removed, turn on and off the switch to
check the normal switching operation of the micro switch using a circuit tester.
e) If the hydraulic line for the capacity control of the compressor is opened for overhaul or other work,
use nitrogen gas or compressed air to set the unloader piston to the no-load and full load positions
and check if the micro-switch can detect the 0 % and 100 % positions of the micro-switch cam.
f) Carry out other visual inspection including any indication of water intrusion in the indicator, any rust
on switch terminals, any wear of the switch roller or micro-switch cam, and so on.
5.5.12.3 Reassembly
To carry out the reassembly, follow the disassembly procedure in reverse. Lastly, correctly adjust the
indicator needle position according to the following procedure:
a) If the hydraulic line for the capacity control of the compressor is opened for the purpose of overhaul
or other work, use nitrogen gas or compressed air to set the unloader piston to the no-load position.
Then, set and fix the indicator needle to the origin of the figure to show the rotation on the dial.
Next, set the piston to the full load position. Make sure the indicator needle points to the end point of
the figure on the dial.
b) In the normal condition where the hydraulic line for the capacity control is not opened, use the
manual capacity control circuit to move the piston.
While the control power is turned on, the indicator cover must be mounted to prevent possible
electric shock.
Then, after the piston position is fixed, control power is turned off, and the lock-out and tag-out
procedures are completed, remove the indicator cover and secure the indicator needle in position.
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