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Section 4 • Operation
Dual Oil Filters
On compressor units equipped with dual oil filters, only
one filter should be in operation at a time.
During operation, both oil filter outlet shut-off valves
should be open. This will help minimize the sudden loss
of oil pressure when switching between oil filters for
servicing.
Refer to Oil Filter Replacement in Section 5 for further
details.
Control System
Calibration
Equipped for automatic operation, the screw compres-
sor unit has safety controls to protect it from irregular
operating conditions, an automatic starting and stop-
ping sequence, capacity and volume ratio control
systems.
Check all pressure controls with a remote pressure
source, to assure that all safety and operating control lim-
its operate at the point indicated on the microprocessor.
The unit is equipped with block and bleed valves that
are used to recalibrate the pressure transducers. To use
the block and bleed valves to recalibrate the pressure
transducers, the block valve is shut off at the unit and
the pressure is allowed to bleed off by opening the bleed
valve near the pressure transducer enclosure. The trans-
ducer can then be calibrated at atmospheric pressure (0
psig), or an external pressure source with an accurate
gauge may be attached at the bleed valve.
The discharge pressure transducer cannot be isolated
from its pressure source, so it is equipped with only a
valve to allow an accurate pressure gauge to be attached
and the pressure transducer calibrated at unit pressure.
Recheck the transducers periodically for any drift of cali-
bration, refer to maintenance/service interval table in
Section 5.
4 – 2
NOTE
VSS/VSM/VSH/VSSH • Installation, Operation and Maintenance Manual • Emerson • 35391SD
Starting, Stopping and Restarting The
Compressor
For additional control information, refer to micro-proces-
sor manual ( 35391SC for Vission20/20 Operating Manual
or 35391CM for Compact Logix PLC Software Manual).
WARNING
Software programming credentials shall only be
made available by the supplier. The user will only
have access to operational features established by the
supplier. Failure to comply may result in serious injury
or death.
Starting
Before the screw compressor unit can start, certain con-
ditions must be met. All of the safety setpoints must be
in a normal condition, and the suction pressure must
be above the low suction pressure setpoint to ensure a
load is present. When the "ON/OFF" switch or "Manual-
Auto" button is pressed, the oil pump will start. When
sufficient oil pressure has built up and the compressor
capacity control and volume ratio slide valves are at or
below 10%, the compressor unit will start.
The amount of oil pressure that needs to be achieved
before compressor start is at least 6 psig above the
discharge pressure. For additional information on
Low Oil Pressure at Start, see Troubleshooting Guide -
General Problems and Solutions in Section 6.
If the compressor is in the automatic mode, it will now
load and unload and vary the volume ratio in response
to the system demands.
Stopping/Restarting
Stopping the compressor unit can be accomplished a
number of ways. Any of the safety setpoints will stop
the compressor unit if an abnormal operating condition
exists. The compressor unit "On-Off" or stop button will
turn the compressor unit off as will the low pressure set-
point. If any of these conditions turns the compressor
unit off, the slide valve motors will immediately energize
to drive the slide valves back to 5% limit. The control mo-
tors will be de-energized when the respective slide valve
moves back below 5%. If there is a power failure, the
compressor unit will stop. If the manual start on power
failure option is selected, restarting from this condition
is accomplished by pushing the reset button to ensure
positive operator control. If the auto start on power fail-
ure option is selected, the compressor unit will start up
after a waiting period. With both options, the compres-
sor slide valves must return below their respective 5%
limits before the compressor unit can be restarted.
NOTE
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Table of Contents
Troubleshooting
