Operation & Maintenance Process Equipments

Troubleshooting in Pumps

Problems with pumping equipments cause not only inconvenience, but can also contribute to loss of production. An efficient operation depends on trouble-free pumping.

The following table lists problems that often occur with pumps with probable symptoms and the possible causes pertaining to  them.

Symptom

Possible Causes

1. Insufficient pump capacity
  • Suction pipeline not fully filled with fluid.
  • Insufficient NPSH.
  • Excessive gas in liquid.
  • Air leakage into the pump or to the suction line.
  • Partial blockage of impeller.
  • Worn-out bearing rings.
2. Pump does not deliver
  • Pump not primed.
  • Insufficient margin between suction pressure & vapour   pressure at suction condition (insufficient NPSH).
  • Air pockets in suction lines.
  • Air leaks into suction lines.
  • System head higher than pump total head.
  • Parallel operation of pumps with different characteristics.
  • Foreign material in the pump impeller.
3. Pump loses priming after start-up
  • Insufficient filling of suction piping.
  • Insufficient NPSH due to pressure variation at suction.
  • Air or gas entry to pump.
  • Variation of submergence.
4. Motor getting overloaded
  • Pump operates at higher speed.
  • Higher system head.
  • Lower system head.
  • Different specific gravity of liquid.
  • Different viscosity.
  • Improper fixing of packing.
  • Rubbing of rotating parts with stationary parts.
5. Vibration of pump
  • Gas entry into pump.
  • Operation at capacity less than minimum flow.
  • Foreign material in impeller, causing imbalance.
  • Misalignment.
  • Damaged bearings.
  • Foundation not rigid.
  • Shaft bent.
  • Rotor imbalance.
6. Frequent damage of bearings
  • Misalignment.
  • Bent shaft.
  • Worn-out bearing (spurious).
  • Shaft eccentricity due to misalignment.
  • Excessive thrust due to worn-out balancing hole or due to blockage.
  • Excessive grease or oils in bearings.
  • Insufficient lubrication.
  • Incorrect fitting of bearings.
  • Excessive cooling of bearing housing.
  • Rusting of bearing due to water entry.
7. Seizure of rotors
  • Entry of foreign material.
  • Rotating part rubbing.
  • Worn-out bearings.
  • Insufficient clearance of bearing rings.
  • Lube oil failure.

 

Frequent troubles for specific pump types

Centrifugal Pumps: Hydraulic troubles, like failure to deliver any liquid, low discharge pressure, and others, are more common and more difficult to solve. It is estimated that, except for mechanical defects, about 85% of the troubles met with centrifugal pumps occur on the suction side of the unit.

Reciprocating Pumps: Typical common troubles include failure to discharge, low discharge pressure, short stroking, speed too high, long-stroking, vibration, stalling, discharge-pressure fluctuation and excessive stuffing-box leaks.

Rotary Pumps: The most common troubles in rotary pumps are failure to discharge, excessive noise, rapid wears, reduced capacity, excessive power consumption, and loss of suction.

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