Pump service and repair

Are you noticing some noise, vibration, and reduced performance in your pump? Here are some common problems

you may face:

Centrifugal Pumps

Dry Running
During normal operation of a centrifugal pump, the fluid handled surrounds the flow space inside the pump, across gap seals on the impellers and mechanical seals in the pumps. The liquid lubricates the components in contact with each other and exercises a centring action in the clearance gaps of the impellers and shaft passages such that the pumps are able to work without the rotor touching the casing.

Without adequate liquid, dry running can occur in certain areas because of insufficient cooling and centring action. The consequences are overheating, abrasion, seizure of the materials, vibrations and other phenomena which may in due course lead to the complete disintegration of the pump.

 Dry running causing the shaft to break in the pump

Cavitation occurs when the liquid in a pump turns to a vapor at low pressure. It occurs because there is not enough pressure at the suction end of the pump, or insufficient Net Positive Suction Head available (NPSHa). When cavitation takes place, air bubbles are created at low pressure. As the liquid passes from the suction side of the impeller to the delivery side, the bubbles implode. This creates a shockwave that hits the impeller and creates pump vibration and mechanical damage, possibly leading to complete failure of the pump at some stage.

Causes often occur at the design stage where the pressure at the inlet fails to account for friction loss or velocity head loss, and the inlet and outlet losses have been accurately considered within the suction pipework of the pumping system. Because of this, during the design phase, it is necessary to calculate these losses and process unit losses in the suction pipework and then deduct those losses from the suction head available to the pump.

Cavitation Incident in 2019

Common Problems of Centrifugal Pumps
Air Operated Diaphragm Pumps (AODD) Pumps

Diaphragm Rupture
Usage of an AODD pump results in mechanical stress and over time it causes stress cracks and failure. Material of the diaphragm combined with the method of manufacturing plays an important role in the longevity of diaphragms. The higher the pressure used in operations the higher is the stress on the diaphragm. Lastly the total number of strokes is the ultimate measure for the lifespan of the diaphragm. Pumps that run faster will likely fail more quickly, and it is important to routinely change your diaphragm to prevent downtime.
Check Valve Failure
These check valves are likely to fail due to something getting in between the ball and the seat preventing a good firm leak-proof closing of the valve. Use of a strainer will reduce this possibility. Additionally flushing the pump when you suspect something is stuck often clears the check valves of debris. Wear of the ball and seat also causes leak paths. This wear could be due to abrasive particles in the liquid or just a matter of poor material choice for balls or seats.

Air Valve Stalling or Leakage
This occurs when leakage of air where the air mostly blows through the valve instead of being redirected to push the diaphragm. Clogging on the other hand could be due to the quality of the air you are using.

Common Problems of AODD Pumps