Pump Repair FAQ

Pump Repair FAQ

Answers To Your Pump Repair Questions

At OTP, we’re always getting questions from customers about pump repair. Here are some of the most frequent queries we receive—and the answers to go with them. Need more answers? Simply contact one of our pump repair experts today.

Q: We installed our pump after repair, but it still makes noise and underperforms. Why?

A: Follow these steps to check your process and ensure it has not changed:

  • Valves: Check all valves in line to the pump; a valve may not be properly adjusted.
  • Flow: The flow to the pump may have changed; verify total flow and compare to the pump curve.
  • Piping: Verify that no piping changes were made to cause a drop in head pressure, which can cause the pump to dead head.
  • Temperature: The temperature of the material may be too hot, causing cavitation.
  • Pump Oversized/Undersized: The pump conditions may have changed since the original installation; verify the operating conditions and compare to the pump curve to assure proper sizing.

Q: What is cavitation?

A: Cavitation means that cavities or bubbles are forming in the liquid being pumped. Symptoms of cavitation include excessive noise and vibration and loss of capacity, pressure and efficiency.

Q: My pump used to work, but now it is exhibiting the noise and vibration symptoms of cavitation. What might have changed?

A: System changes affect pump performance and can cause cavitation. Check for a loss of suction pressure, an increase in fluid velocity or an increase in inlet fluid temperature.

Q: Why is my pump losing pressure and making noise?

A: Lost pressure and noise result from a couple of common causes, including:

  • Misalignment of the pump and driver
  • Improper support for the piping
  • Loose foundation or anchor bolts
  • Liquid viscosity that is too high
  • The pump may be operating below its minimum recommended safe flow

Q: When should I remove my pump from service for an evaluation or repair?

A: When a pump no longer delivers the required flow and pressure, the pump may require rebuilding to restore the original performance. However, there may be other conditions that affect the pump’s performance that should be reviewed before assuming the pump is the problem. These include:

  • Clogged inlet strainer or discharge filter
  • Partially closed valves
  • Low-relief valve setting on

There are many conditions in which you may consider a pump ‘failed’ and pull it for evaluation, including:

  • Excessive vibration or noise level
  • Casing, seal and stuffing box begins to show heavy leakage
  • Shafts deflect or shear
  • The shaft or impeller will not turn
  • Close tolerances erosion
  • Cavitation
  • Contamination of oil

Q: Why would a motor draw high amp or trip the breaker on my pump?

A: There are numerous reasons a pump can pull high amp readings or trip breakers. Some common causes include:

  • The shaft is running in the wrong direction
  • Misalignment between the pump and driver
  • Pipe strain
  • A bent shaft
  • Cavitation
  • Water hammer
  • Operating off the best efficiency point (BEP)
  • Thermal growth
  • Pulley driven pumps
  • Bearings are beginning to fail
  • The specific gravity of the fluid has increased
  • The viscosity of the liquid is increasing with a change in temperature
  • The viscosity of a liquid can increase with agitation
  • The impeller is rubbing against the casing
  • The impeller has been installed backwards
  • The open impeller needs adjusting

Q: Why is dynamic balancing important for a quality pump repair?

A: Unbalance in rotating parts creates forces that produce vibration in operating equipment. Simply put, unbalanced parts cause downtime! Typical modes of failure due to unbalanced parts include:

  • Bearings: Bearings will see an increased load.
  • Mechanical seal: Vibration may cause the seal faces to separate or cause the carbon faces to bounce against hard surfaces, both leading to failures.
  • Shaft damage: Increased fretting under both grease seals and mechanical seals.

Dynamic balancing increases the mean time between failures (MTBF); this will assist in the creation of increased run times and minimize unscheduled downtime.

Q: Why is laser alignment important and when should it be performed?

A: Misalignment of rotating equipment is a leading cause of premature failure. Laser alignment assures the equipment is installed according to manufacturers’ recommendations, reducing the risk of excessive loading of the equipment’s bearings or other internal components.

Based on the type of pump, both an initial laser alignment and “hot alignment” may be necessary. A “hot alignment” is completed after the pump has run under load for a certain amount of time. After the recommend amount of time, lockout the system and perform the “hot alignment” to permit adjustment for any thermal growth or changes that may have occurred.

Q: Why is there a seal sensor on my submersible pump?

A: A seal sensor in a submersible pump provides a warning to the pump operator that the mechanical seal has been compromised or has failed. In most pumps equipped with a seal sensor, the pump will have a double mechanical seal. The outboard (or product side) seal is normally the first to fail. Once water has entered the seal chamber, the sensor will detect the presence of water and signal the alarm. The pump may be safe to run for a short time, but it should be shut down as soon as possible to avoid water leakage into the motor chamber which would cause serious damage to the motor.