Author: Mike Moyer, Carver Pump
Pumps require a certain amount of pressure to be able to operate reliably. To ensure long service life the pump selected must be able to operate without excessive cavitation, which is what happens when suction pressure drops too far causing tiny bubbles within the liquid that burst and cause damage to the internal pump components (including impellers, shaft, etc.).
This is why careful attention is paid to Net Positive Suction Head (NPSH). There are two important parts of understanding NPSH: there is NPSHa (“a” stands for ‘available’ and represents the absolute pressure at the suction port of the pump) and NPSHr (“r” stands for ‘required’ and means the minimum pressure required at the suction port of the pump). Defining the correct NPSHa and NPSHr is important for the pump selection process, because if NPSHr is greater than NPSHa, then damaging cavitation could result. What happens when a situation arises where you cannot find the ‘perfect’ pump to meet the suction conditions of a specific application? One available alternative is to use a pump inducer. A pump inducer is a component that can be added to the axial inlet portion of a centrifugal pump rotor, the function of which is to raise the inlet head by an amount sufficient to provide the required pressure and prevent significant cavitation in the pump.
NPSH Curve with and without an Inducer
There were two recent instances where Carver Pump successfully applied inducer technology to help design engineers solve a pump selection problem. A refinery engineering team in Venezuela wanted a vertical inline pump to process 25 gallons per minute at 153.4 feet of head. Only 3 feet of suction pressure was available, but the pump impeller required 6 feet of suction pressure. To address this low suction pressure issue, the engineers at Carver Pump developed a pump inducer that allowed the pump to operate with fewer than 3 feet of NPSHa.
At an oil refinery in Canada, the engineers at Carver Pump addressed a situation on the opposite end of the spectrum. Instead of smaller pumps, this refinery was dealing with a very large pump that did not have enough suction pressure available. An inducer was introduced to reduce the required NPSH and promptly solved the issue.
While using pump inducers are not a typical approach to meeting suction requirements, they can be found in many applications where there is not enough pressure available to feed the pumps. In applications such as boiler feed, power generation, and even chemical processing plants, pump inducers provide options when design engineers get ‘boxed into a corner’ or are working with tricky applications. A pump inducer can add to almost any centrifugal pump – even API pumps. Just keep in mind that when you put an inducer on a pump, it narrows the window of pump performance.
Carver Pump works one-on-one with our customers to provide support during the pump selection process – even for challenging applications. If you are having issues selecting pumps that meet your suction pressure requirements, ask us if a pump inducer might work for you. Pump inducers can certainly open up the realm of possibilities.
About Carver Pump
Since we built our first pumps in 1938, Carver Pump has become recognized as one of the leading centrifugal pump companies, building pumps to the most demanding engineering specifications and military standards in the world. We were one of the first American pump companies to attain ISO 9001 certification – the most recognized standard for quality in the world. This certification is your assurance that our commitment to quality includes not only our hardware, but also superior customer service, leading-edge R&D, and continuous improvement in everything we do. So whether the job is refueling fighter jets on the deck of an aircraft carrier, supplying paint to an auto assembly line, or bringing water to the fountain in a city park, we put our reputation on the line everyday with every pump we build. Learn more at www.carverpump.com.
