Emerson VSR, VSM, VSS service manual Operation, Thermosyphon Oil Cooling

Operation

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

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