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discussed in Section 1, Compressor Installation. These
methods are either suction valve unloading (utilizing
suction valve unloader towers), or Inlet Shutoff Valve
unloading (either the solenoid or actuated ball valve
type). See Section 1, Compressor Installation for
additional information on these two methods, and on
the proper installation procedures.
Adjustment of either of these methods is done via the
control panel. Standard control panels use pressure
switches to sense the inlet and discharge pressures
(as necessary), and open or close the unloader device
based upon this pressure. Additional timer relays
allow for unload timeout operation as well as unloaded
startup operation.
Suction Pressure Switch
- This switch is set at the
factory at the design value setpoint to prevent the
compressor from operating under low suction pressure
conditions. The switch is
fi
eld adjustable and may
require
fi
ne tuning to actual inlet pressure conditions
(see Figure 21b). The sensing line should be routed
from a nearby inlet receiver tank directly to the switch.
Contact the factory if adjustments of more than 5%
are required.
Discharge Pressure Switch
- This switch commonly
has two adjustments: one for the discharge pressure
setpoint and the other for deadband (the range of
falling discharge pressure before the compressor loads
again). Both can be
fi
ne tuned to process requirements
(see Figure 21b). Avoid narrow deadbands which
result in frequent cycling of the compressor (load/
unload). The sensing line should be routed from a
nearby discharge receiver tank directly to the switch.
Contact the factory if adjustments of more than 5%
are required.
Unload Timeout Timer (UTO)
- This timer relay is
set at the factory so the compressor motor will shut
down after a pre-set amount of time when running in
an unloaded state. Generally, this length of time is 10-
20 minutes. Adjustment may be made to
fi
ne-tune the
compressor system for maximum operational ef
fi
ciency
and minimum energy consumption (see Figure 21a).
Unload Startup Timer
- This timer relay is set at the
factory so the compressor will run unloaded for 8-12
seconds at startup, allowing oil pressure to build before
loading (see Figure 21a). The time must be set longer
than the Low Oil Pressure Timer.
PLC Based Control Panels
- These panels use
transducers to sense the inlet and discharge pressures.
Adjustments are done through the digital interface
display screen. Unload timeout and unloaded startup
operation are also adjusted through the display screen.
Generally a PLC supplement manual will accompany
any compressors sytem with a PLC control device.
ADDITIONAL CONTROLS
ADJUSTMENT
Hycomp tests and adjusts all compressors at the factory
to perform to the requirements of the sales contract.
Bare compressors are factory tested for operability.
Compressors with integrated control system packages
are fully tested for operational viability.
Field adjustment are often required to accommodate
minor variations in actual operating conditions or
requirements. Speci
fi
c adjustment methods for the
devices are contained in the applicable accessory
Constant Speed Unloader
P/N RV006, RV007,
or RV008
Unload Pressure
Setpoint Adjustment
Differential
Pressure
Adjustment
Manual
Shutoff
Figure 20: Constant Speed Unloader Valve (Pilot Valve)