FAQ’s

Centrifugal Pumps convert rotational kinetic energy into hydrodynamic energy in the form of positive flow and pressure. Centrifugal pumps are aptly named due to their application of centrifugal force. A long-studied and hotly debated physical phenomenon is used to explain the outward force that appears to be applied upon a mass rotating about a fixed axis. When harnessed in this particular fashion, fluid entering the pump’s casing is flung outward by the vanes of the rotating impeller, and the kinetic energy generated by this motion is captured by the pump casing which guides the fluid toward the discharge port. Today there exists a seemingly infinite number of centrifugal pump designs, but many can be categorized accordingly into the types listed below:

• End-suction pumps
• In-line pumps
• Double suction pumps
• Vertical multistage pumps
• Horizontal multistage pumps
• Submersible pumps
• Self-priming pumps
• Axial-flow pumps
• Regenerative pumps

The term ‘stage’ in the context of pumps simply refers to the number of impellers within a centrifugal pump. A single-stage pump uses just one impeller, and a multi-stage pump utilises two or more impellers in hydraulic series. The number of impellers generally correlates to the maximum output pressure that a centrifugal pump can achieve, hence why multistage pumps of either the vertical or horizontal type are utilised in pressure boosting applications (where overcoming static as well as dynamic head is necessitated) whereas single stage pumps tend to be utilised in closed-loop systems such as heating and cooling applications where resistance to flow is much lower.

Cavitation is the technical term used to denote the formation and subsequent collapse of microbubbles in a pumped liquid. Cavitation can occur when the Net Positive Suction Head available (often abbreviated as NPSHa) drops below the Net Positive Suction Head required (NPSHr) by the pump at the necessary flow rate. Bubbles or cavities form within a pump’s chamber or casing when the pressure exerted upon the fluid falls below its vapor pressure. When the liquid reaches the outer edges of the impeller, the higher relative pressure applied to the liquid causes these bubbles to violently collapse causing surface damage to the wetted parts found within the pump. The occurrence of cavitation can present itself in the form of a crackling, or a popping sound from within the pump chamber when the pump is running. If cavitation does not present itself in an obvious manner and is therefore not adequately addressed (often by simply increasing the NPSHa) pump failure can occur with almost immediate effect.
Here are some common signs that a pump is cavitating:

• It sounds like there is gravel or marble within the pump chamber.

• Excessive power consumption has become the norm.

• The pump has begun to leak (likely due to seal and/or bearing failure – this is arguably the most common of all types of pump failure so be sure to check for other signs of cavitation before assuming that this is the sole root cause).

• Upon strip down and inspection, the pump impeller and/or shaft appear to show signs of surface damage.

The best way to avoid cavitation is to install any pump in strict accordance with the manufacturer’s advice and/or guidance. Prevention is always better than the cure and this sentiment certainly rings true concerning pumps.
Should you have any concerns over cavitation, our engineers have been rigorously trained to identify and rectify the causes of a multitude of common pump failures – often before failure has even occurred. Whilst most common forms of breakdowns prove to be ultimately unavoidable in the long-term, enlisting the help of a company with over 30 years of experience in the supply, installation, and maintenance of a wide array of manufacturers, models, and pump designs certainly won’t hurt your hopes of maintaining a healthy, functioning and optimised pump system!
Get in touch with us today to discuss your pumping requirements!