Page 37 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

22 Major Process Equipment Maintenance and Repair

4. Pump case should be vented. (Open vent at top of pump casing until
ail air is expelled from casing.)
5. If product is hot, ample time should be allowed for pump case to
heat up. (Pump case and rotating assembly could distort from un-
even heat transfer.)
6. Before starting, rotate pump shaft by hand. (Should be free, no rub-
bing.)
7. Crack open discharge valve-don’t fully open. (A centrifugal pump
uses less horsepower at start-up with the discharge valve nearly
closed; also this practice will prevent initial cavitation.)
8. Start Pump, watch discharge pressure gauge, and as soon as pump
pressure stabilizes , open discharge valve slowly. Watch discharge
gauge; discharge pressure will fall off for a few turns of the valve
until existing head conditions are met. Once pressure stabilizes,
you can fully open the discharge valve.
Important! Never allow pump to run too long with discharge valve
closed.

The Pump in Operation
1. During operation, a centrifugal pump requires occasional inspec-
tion (Data sheets in Appendix 1B may prove helpful).
2. Make sure that there is flow as the discharge valve is opened by
watching for a drop in discharge pressure.
3. Watch for fluctuations in suction and discharge pressure to make
sure the pump does not cavitate.
4. After the pump has run for a few minutes, the operator should touch
the pump and motor bearings to determine if they are overheating.

Note: The Operator always touches the motor with the back of the
hand so that in case of shock the hand can be pulled away.

5. The mechanical seals should be checked for leakage particularly
during the first hours of operation. A minor leak through the seal
usually stops after a short time, but if it continues, the pump should
be stopped and the seal fixed.
6. When operating the pump at a discharge pressure below the rated
point, the motor should be watched carefully. The discharge valve
should be throttled to build up head to a safe point. Should the low
head condition persist, the pump should be shut down. Centrifugal
pumps should not be operated at greatly reduced capacity or with
the discharge valve pinched because the energy required to drive
the pump is converted into heat and the temperature of the liquid
may reach the boiling point. Furthermore, many pumps are subject
to flow instability at low flows.