HPS Rotary Screw Compressor Units
070.700-IOM (MAR 21)
Page 35
Maintenance
Motor bearings
Follow the motor manufacturer’s maintenance
recommenda tions for lubrication.
Warning
Make sure the motor bearings are correctly lubricated
before start-up as required by the motor manuf ac turer.
Grease compatibility
The motor nameplate lists the manufacturer’s recom-
mended grease. Using grease other than that recommend
-
ed by the manufacturer may result in premature motor
failure and denied warranty claims. The correct grease
is available through the Baltimore Parts Center or motor
supplier.
Troubleshooting guide
Successful problem solving requires an organized ap-
proach to define the problem, identify the cause, and
make the appropriate correction. Sometimes it is possible
that two relatively obvious problems combine to provide
a set of symptoms that can mislead the troubleshooter.
Be aware of this possibility and avoid solving a potentially
wrong problem.
Abnormal operation
analysis and correction
Four logical steps are required to analyze an opera tional
problem effectively and make the necessary correc tions:
1.
Define the problem and its limits.
2. Identify all possible causes.
3. Test each cause until the source of the problem is
found.
4. Make the necessary corrections.
The first step in effective problem solving is to define the
limits of the problem. If, for example, the compressor pe-
riodically experiences high oil tempera tures, do not rely on
this observation alone to help identify the problem. On the
basis of this information the apparent corrective measure
would appear to be a readjustment of the liquid injection
oil cooling system. Lowering the equalizing pres sure on
the thermal expansion valve would increase the refriger ant
feed and the oil temperature drops.
If the high oil temperature was the result of high suction
superheat however, and not just a matter of incorrect
liquid injection adjustment, increasing the liquid feed could
lead to other problems. Under low load conditions the
liquid injection system may have a tendency to overfeed.
The high suction superheat condition, moreover, may only
be temporary. When system conditions return to normal,
the unit’s liquid injection overfeeds and the oil tempera-
ture drops. In solving the wrong problem a new problem
was created.
When an operating problem develops, compare all operat-
ing information on the main operating screen with normal
operating conditions. If there is maintained operating log,
this log can help determine what constitutes normal op
-
eration for the compressor unit in that particular system.
The following list of
abnormal system conditions can cause
abnormal operation of the HPS compressor unit:
•
Insufficient or excessive refrigeration load.
•
Excessively high suction pressure.
•
Excessively high suction superheat.
•
Excessively high discharge pressure.
•
Inadequate refrigerant charge or low receiver level.
•
Excessively high or low temperature coolant to the oil
cooler.
•
Liquid return from system (slugging).
•
Refrigerant underfeed or overfeed to evaporators.
• Blocked tubes or plates in water-cooled oil cooler from
high mineral content of water.
•
Insufficient evaporator or condenser sizing.
•
Incorrect refrigerant line sizing.
•
Incorrect system piping.
• Problems in electrical service to compressor unit.
• Air and moisture present in the system.
Make a list of all deviations from normal plant operation
and normal compressor unit operation. Delete any items
that do not relate to the symptom and separately list those
items that might relate to the symptom. Use the list as a
guide to further investi gate the problem.
The second step in problem solving is to decide which
items on the list are possible causes and which items are
additional symptoms. High discharge temperature and high
oil temperature readings on a display may both be symp
-
toms of a problem and not casually relat ed. High suction
superheat or a low receiver level, however, could cause
both symptoms.
The third step is to identify the most likely cause and take
action to correct the problem. If the symptoms are not
relieved move to the next item on the list and repeat the
procedure until you have identified the cause of the prob
-
lem. After identifying and confirming the cause make the
necessary correc tions.