Method selection
First method
The best method to determine the target discharge temperature is to run
Coolware/Comp1
. Run
Coolware/Comp1
or
ScrewSelect
with the operating conditions of the compressor. The program
will give you a theoretical discharge temperature of the compressor. Once this temperature is
known, you may adjust the hand expansion valve. The ideal discharge temperature is 2.7°C
or -2.7°C of the theoretical discharge temperature. Adjust the valve to achieve the theoretical
discharge temperature.
Second method
If you do not have access to
Coolware/Comp1
or
ScrewSelect
, 82°C is an appropriate target
discharge temperature for a high stage ammonia compressor. Booster applications and
compressors using HFC and HCFC refrigerants may run cooler. Compressors with high discharge
pressure may run hotter.
Choosing the first or second method
Use the
first method
for compressors with external oil cooling (refrigerant-cooled
(thermosyphon), water-cooled, and glycol-cooled).
Before the initial start-up of the compressor, close the hand expansion valve completely. Open the
valve back up and count the turns that it takes to fully open the valve. After the initial start-up, close
the valve to achieve approximately 82°C discharge temperature or the theoretical temperature
from Coolware. Do not fully close the valve at any time while the compressor is running.
Use the
second method
for compressors with liquid injection oil cooling. Because the discharge
temperature is controlled by the liquid injection thermal expansion valve, you will not be able to
adjust for the correct oil flow by using the discharge temperature.
Before the initial start-up of the compressor, close the hand expansion valve completely. Open
the valve back up, and count the turns that it takes to fully open the valve. After the initial start-
up, close the valve halfway. If it took 10 turns to open the valve completely, then turn it 5 turns. If it
took 7 turns to open, then close the valve 3 1/2 turns. Do not close the valve any more than 1/2 the
number of turns required to fully open it.
CAUTION
Failure to properly adjust the hand expansion valve may lead to excessive noise and vibration of the
compressor and unit, premature failure of the bearings, liquid loading of the rotors, liquid starvation of
the rotors, and catastrophic failure of the compressor.
Initial start-up guidelines
Adhere to the following guidelines during the initial start-up:
• For reliable and safe operation, the compressor must run at the proper speed and discharge
pressure. Exceeding design conditions creates a potential hazard.
• Rotate and lubricate the motor bearings according to the manufacturer’s recommendations
before
initial start-up, as required.
• After running the unit for approximately three hours, adjust the liquid injection oil cooling, if
applicable. If the unit has water-cooled oil cooling, adjust the water control valve to cooler.
• The compressor slide valve and slide stop linear transmitters should be calibrated.
• Perform a vibration analysis, if the necessary equipment is available.
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SAB 283-355 A-Frame OHU 6042 and OHU 7650 (including ATEX) Screw Compressor Unit
