Troubleshooting Self Priming Pumps

When a self-priming pump underperforms, the issue is often not the pump itself but the surrounding system. Gauge readings are one of the most effective tools for diagnosing problems quickly.

What Your Gauges Are Telling You

• High discharge pressure → blockage or restriction in the discharge line
• High suction pressure → blockage in the suction line
• Low or no suction pressure → suction air leak
• Fluctuating suction pressure → vortexing or air entrainment
• Low suction and discharge pressure → internal pump issue

Understanding these indicators helps narrow down the root cause before dismantling equipment.

Common Self-Priming Pump Issues

Noisy Operation

First, determine whether the noise is mechanical or hydraulic:

• Drain the pump casing and briefly run the pump dry.
• If the noise remains, inspect for loose hardware or bearing wear.
• If the noise disappears, the issue is hydraulic.

Cavitation

Cavitation is the most damaging hydraulic issue and sounds like gravel or marbles inside the pump. It occurs when local pressure drops below the liquid’s vapour pressure, forming vapour bubbles that collapse violently.

Common causes and fixes:

• Suction cavitation (high suction pressure):
  • Clear suction blockages
  • Increase suction pipe diameter
  • Reduce suction lift
    
    
• Discharge (tip) cavitation (high discharge pressure):
  • Remove discharge restrictions
  • Increase discharge pipe size
  • Reduce static head or verify operating speed

Always compare gauge readings and RPM against the manufacturer’s performance curve.

Vortexing

If the suction gauge fluctuates and the pump growls, air may be entering via surface vortexing.

Solutions include:

• Lowering the suction inlet
• Increasing inlet diameter (suction bell)
• Reducing pump-off level

Pump Won’t Prime or Is Slow to Prime

This usually indicates a suction air leak.

• Wrap joints with cling film and observe where it is drawn in.
• Repair leaking joints immediately.

If no leak is found, the suction line may be too long or incorrectly sized. In some cases, adjusting speed or installing a properly designed trap can help.

Pump Stops or Fails to Deliver Rated Flow

Check gauge readings:

• High suction pressure → blocked suction line
• High discharge pressure → blocked discharge line
• Low readings on both → internal clearance issues or a partially blocked impeller

Frequent Blockages

If blockages are common:

• Confirm where the pump operates on its performance curve
• Operating too far left may result in insufficient velocity
• If operating near BEP and blockages persist, the pump may not be suitable for the solids content

In some cases, an upgraded impeller or a different pump design is required.

When to Get Expert Support

Persistent issues often indicate a mismatch between pump selection and application conditions.

Allflo Pumps & Equipment can assist with diagnosing self-priming pump issues and recommending corrective actions to improve reliability and performance.

Speak with our team to discuss your pumping system.