48
As the oil and desupserheating load varies, the
temperature controller adjusts the speed of the
pump/motor combination to maintain a constant
oil temperature.
NOTE:
See separate V-PLUS® instruction manual for de-
tailed start-up and operation.
4. Thermosyphon Oil Cooling
Using a brazed plate or an one pass shell and tube
type vessel, similar to the water cooled oil cooler,
oil is circulated on the shell side and liquid re-
frigerant from the receiver is circulated through
the tubes. Thermosyphon systems use a 3-way
temperature sensing control valve to regulate oil
at 120°F. Oil is bypassed around the thermosyphon
oil cooler. When oil is higher than 120°F, the oil is
passed through the thermosyphon oil cooler. A
1/4” tubing line w/valve adds high pressure gas to
the oil to quiet the sound of injection. Open this
valve in small amounts, until noise subsides. The
closed type cooling circuit is free from the foul-
ing problems associated with open circuit water
cooling. Since the oil cooling load is rejected in
the condenser, this type of cooling is practical.
The temperature limits here are the same as those
regarding the water cooled oil coolers.
5. Oil Pump
This system is designed to provide adequate com-
pressor lubrication when there is low differential
oil pressure across the compressor suction and
discharge for some high stage applications and
booster applications as required.
On start-up, the control system will calculate the
pressure differential between the compressor oil
manifold & suction pressure. If this differential
pressure ratio is less than 2.8:1, then the oil pump
will turn on and will continue to run until the pres-
sure ratio is 3.0:1.
CONTROL SYSTEM
Equipped for automatic operation, the screw com-
pressor unit has safety controls to protect it from
irregular operating conditions, an automatic start-
ing and stopping sequence, capacity and volume
ratio control systems.
Check all pressure controls with a remote pres-
sure source, to assure that all safety and operating
control limits operate at the point indicated on the
microprocessor.
The unit is equipped with block and bleed valves
that are used to recalibrate the pressure transduc-
ers. 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 transducer 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 iso-
lated 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 calibration.
A. Screw Compressor Control And Operation
1. Starting, Stopping and Restarting the Com-
pressor.
Before the screw compressor unit is started,
certain conditions 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 assure that a
load is present. When the “On-Off” switch or
Operation
