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Centrifugal Pump Troubleshooting Guide

by PSG

With over 70 years’ experience in the industry, we feel like we’ve seen a thing or two when it comes to pump operations. As with most heavy-duty equipment, centrifugal pumps may encounter issues on occasion. Because nobody likes the downtime caused by extensive repair time or parts replacement, we want to share with you our handy, quick troubleshooting guide for common centrifugal pump problems.

We created this guide so that if you experience any of these at your operation, you’ll have a starting point to a solution at your fingertips.

The following are some common centrifugal pump problems, their likely causes, and what to do about them.

 

  1. If No Liquid Is Delivered

    You may encounter a situation where your pump is not delivering the liquid consistently – or at all. This can occur even if the pump has been operating normally, and both the discharge and suction valves are open and functional. There are several potential causes for a stoppage in liquid delivery. Fortunately, there are remedies as well:

    • The pump is not primed: re-prime the pump and verify that the suction line is full of liquid.
    • There’s an obstruction in the suction line: inspect the line and remove any obstruction.
    • The impeller is clogged: inspect the impeller and remove the obstruction.
    • Rotational direction is wrong: doublecheck the correct rotation and change if possible (WARNING – this could be the sign of impending severe damage).
    • The foot valve or suction pipe has inadequate submergence: check the suction source for vortexing and correct submergence and adjust as necessary.
    • The suction lift is too high: review and revise the suction level until corrected.
  2. If the Pump Does Not Produce Rated Flow or Head

    Your pump may seem to be operating properly, with the discharge and suction valves open and fluid flowing through the system. However, you may still notice that the flow rate or head in the system is below rating. Here are some possible causes and solutions:

    • There’s an air leak through the gasket: replace the gasket and tighten all connections properly
    • There’s an air leak through the stuffing box: inspect the packing and mechanical seals and add pressurized flush if necessary.
    • The impeller is partially clogged: this is usually accompanied by a vibration or rattling noise. Inspect the impeller for debris and remove the obstruction(s).
    • There’s excessive impeller clearance: adjust the impeller clearance to correct distances.
    • There’s inadequate suction head: review the design to make sure specs are met and revise if needed.
    • The impeller is worn or damaged: inspect the impeller performance and replace as needed.
  3. If the Pump Bearings Run Hot

    Heat is a danger to centrifugal pumps, so you’ll always want to monitor this. You may encounter an issue where the pump appears to be operating normally and near rating for system flow and head, yet the bearing temps are hot. Here are the probable causes and what to do about them:

    • There is improper alignment: one of the most common causes of bearing friction – which leads to excessive heat – is misalignment. Re-align the pump and driver if you suspect the alignment to be off center.
    • There is improper lubrication: friction and heat increase when the bearings run dry. Check for the correct lubricant (non-foaming) as well as the right levels for the proper quantity and applicability.
    • The bearing cooling is malfunctioning: in some situations, typically in a Griswold® or ANSI pump, a bearing cooler may be present. If the coolant doesn’t circulate properly, it can cause the bearings to overheat. If the pump has a cooler, check the water line(s) and liquid levels.
  4. If the Pump Starts, Then Stops

    Intermittent performance of a centrifugal pump is an obvious sign of an issue. Anything other than smooth, non-interruptive run times should be looked at. If your pump starts and but then the flow stops – and especially if it occurs often – here’s what could be wrong:

    • The pump is improperly primed: sometimes, an incomplete priming (or no-priming at all) can cause the pump to start and stop. Re-prime the pump thoroughly to resolve this issue.
    • There’s air or vapor in the suction line: an accumulation of air bubbles or too much vapor in the suction line can cause the pump to drop out of prime. Review the suction piping and revise as needed to eliminate any air pockets that may be present.
    • There’s an air leak in the suction line: escaping air can also cause intermittent pump runs. Check the gaskets and seals on the pump and replace if needed.
  5. If There Is Excessive Seal Leakage

    Leaks around the pump seals are an obvious sign of a problem, even when the pump is operating at normal hydraulic conditions with the discharge and suction valves open, and the system flow and head are near rating. But before you replace the pump completely, examine the possible causes and solutions for this issue:

    • The packing gland is improperly adjusted: check the gland nuts and tighten them to the correct specification to reduce or stop the leak.
    • The stuffing box is not packed properly: inspect the stuffing box and re-pack if necessary.
    • The shaft sleeve is scored or ridged: if the shaft sleeve is scored or nicked, it can cause leakage at the seals. Replace this part as needed.
    • The mechanical seal is worn: worn seals are a telltale sign of leaks at the seal point. Replace the seals as needed to address this.
  6. If Excessive Power Is Required

    This is another common issue that many operators run into with centrifugal pumps. Even during seemingly normal operation, you may notice the pump is drawing excessive power. Here are some possible causes and solutions:

    • The actual head is lower than what it was designed for: throttle the discharge valve or trim the impeller until it’s properly sized to the head of the system. Then review the design to make sure the head is correct.
    • The liquid is too heavy: if the liquid is heavier than anticipated, the power draw will increase. Review what the correct motor size was designed for and increase the motor power as needed.
    • The stuffing box is packed too tight: if too much material is in the stuffing box, it can force the pump to draw extra power to compensate. Re-pack the pump to the correct levels.
    • The rotating parts are binding: the pump will draw extra power to force movement if a bind occurs. Check the pump internals to see if anything is locking up.
  7. If the Pump Is Noisy or Vibrates

    Noise and vibrations are telltale signs that something is wrong with the pump. Bearing heat can be one possible cause, but there are several other possibilities as well:

    • Improper alignment: if the pump and/or driver are out of vertical or horizontal alignment, it will cause noise or vibrations. Re-align the pump and driver and then monitor the pump.
    • There’s a partial clog in the impeller or the impeller is out of balance: clogs and obstructions in the impeller can cause noise or vibrations, so you’ll want to inspect the impeller to make sure it isn’t clogged or out of balance.
    • There’s a broken or bent impeller or impeller shaft: if any part of the impeller or impeller shaft is broken or bent, it will surely cause noise and vibrations. Inspect these parts and replace as necessary.
    • The pump foundation not rigid: if the hold-down bolts or pump feet are loose, the pump will not remain stable and can vibrate. Tighten down the bolts on the base, pump, and motor. Then re-check the alignment.
    • You may have worn bearings: if the pump bearings are worn, they can create noise as well as dangerous friction. Replace the bearings as needed.
    • The suction and/or discharge piping is not anchored correctly: review the design specs and anchor the piping accordingly.
    • There could be pump cavitation: one of the biggest threats to any pump operation is cavitation caused by excessive vapor. Review the suction system design and correct the problem related to the presence of the air bubbles.

    These are just a few of the most common pump problems you may encounter at your operation and some steps to help resolve them. For more information on pump troubleshooting, click here.