13-9-653 Page 28
Symptom Recommended action
Compressor does
not modulate
On units with TurnValve control, the TurnValve will control delivery
for moderate to heavy demands to maintain the system near the
programmed set pressure, with the inlet valve held open. At light
demands, the inlet valve controls the compressor delivery to
maintain pressure approximately 3 psi above the programmed set
pressure, with the TurnValve held open. If the pressure continues
to rise above these pressures, check that the TurnValve and inlet
valve operate freely, and check wiring and piping to control valves
TVO, TVC, IVO and IVC. If normal modulation does occur, the inlet
valve will be closed during a blowdown as pressure approaches the
high pressure limit.
Compressor cycles rapidly
between load and unload
The external air receiver should be sized appropriately to prevent
cycles. The rapid response time in the CONSTANT RUN mode will
operate with small receivers, but any plant air system will operate
more efficiently with adequately sized storage. Refer to the
operating instructions for further information.
Low reservoir pressure in
CONSTANT mode or other
modes before blowdown
The controller will maintain a minimum pressure in the oil reservoir
while in CONSTANT or in other modes while the blowdown valve is
closed. This occurs only after initially loading the compressor unit.
If reservoir pressure drops while the blowdown valve is closed,
check for leaks between at the reservoir, separator, and connected
piping.
Erratic pressures in
SEQUENCE only
The sequencing system transmits low-level signal between units to
communicate pressures. Units must be properly grounded to a
good ground system, the communications cable should use only
appropriate quality cable, and the cable should be run in its own
conduit.
Compressor cycles rapidly in
SEQUENCE mode only
In the sequence mode, the operating system requires all
compressors be piped directly to receiver, such that all transducers
sense the same pressure. Check valves or restrictions between
compressors and the storage will cause system instability. Run
units in AUTOMATIC mode until the system is corrected.
Error in displayed pressure or
"CHECK XDUCER" while
zeroing
Pressure measurement errors are almost always the result of poor
zero adjustment. This must be done after replacement of a
controller or a transducer. The proper display with all pressure
removed is 0 +1 psig. The adjustment procedure will prevent large
zeroing erros, and recommend that the transducers be checked.
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