NFS Cavitation
A common reason for Pump failure is Cavitation. This can greatly reduce the life of a pump because of the related problems that it can cause.
Cavitation is the result of insufficient pressure at the suction end of the pump or Net Positive Suction Head Available (NPSHa) causing the liquid inside the pump to turn into vapour at low pressure.
At low pressures, this creates air bubbles which implode as the liquid moves from the suction side of the impeller to the delivery side.
The air bubble implosion generates a shockwave that stresses the pumps’ internal surfaces, creating vibration and mechanical damage, and can ultimately result in pump failure.
It is common to think that the pump is at fault, however, causes of flow disruption that result in cavitation are:
- Excessively long inlet piping or suction line
- Too many pipe fittings or a restrictive pipe diameter
- Higher than expected fluid viscosity
- Clogged inlet
- Clogged filters and strainers
- Restricted or collapsed inlet hoses
- Poorly specified pump
- Corroded pipe or fittings
Cavitation can also be caused by restrictions in flow, related to the discharge line such as-
- Clogged filters
- Pipe blockages
- Poor piping design
- Air pockets in the pipeline
Repeated cavitation can cause pitting and fractures in the pump impeller, volutes and casing and in turn weaken the metal. It can also increase resistance to flow and reduce pumping efficiency. The shock loads from cavitation can also effect the shaft, shaft seals, bearings and motor decreasing the service life of the pump.
Cavitation can be avoided during at design stage, ensuring the chosen pump will have sufficient NPSHa so that the liquid remains above vapour pressure.
If you encounter cavitation in your pump system, start by identifying the cause of the pressure drop. In many cases moving the pump closer to the fluid source and removing as many bends and valves as possible corrects the problem.
Blockage in piping or hoses near the pump can also be the source of the problem. Clear all blockages to resolve the issue and clean the suction lines by clearing debris.
Proper installation and routine preventative maintenance can prevent cavitation and prolong the life of your pumping system. National Flow Systems are equipped with a qualified team to specify the
right pump system for your application and with our experienced maintenance team can also provide a maintenance plan to prevent cavitation or resolve the problem causing cavitation.
Back to News