This causes turbulence and pressure pulses throughout the pump which may lead to intense cavitation. Air can be sucked into a pumping system through leaking valves or other fittings and carried along, dissolved in the liquid.
Air bubbles may form within the pump on the suction side, collapsing again with the higher pressure on the discharge side. This can create shock waves through the pump.
This type of cavitation can be prevented by regularly checking all valves and joints, O-rings and mechanical seals for signs of leaks or erosion. To avoid cavitation, the pressure of the fluid must be maintained above its vapour pressure at all points as it passes through the pump. Consequently, it is important to build in a safety margin about 0. Positive displacement pumps require an inlet pressure to be a certain differential greater than the vapour pressure of the fluid to avoid cavitation during the suction phase.
Manufacturers may quote NPIP-R as the recommended inlet pressure and provide charts showing how it varies with pump speed. Cavitation is a potentially damaging effect that occurs when the pressure of a liquid drops below its saturated vapour pressure. Under these conditions it forms bubbles of vapour within the fluid. If the pressure is increased again, the bubbles implode, releasing damaging shockwaves.
This can cause severe erosion of components. A common example of cavitation is when a centrifugal pump is starved of feed: vapour bubbles form in the eye of the impeller as it imparts velocity on the liquid and collapse again on the discharge side of the vanes as the fluid pressure increases. Cavitation can also occur in positive displacement pumps such as gear pumps and plunger pumps.
Contact us. Thank you. There is good information and engineering studies completed in this area. Your empirical results may differ. It is nearly an impossible task to reduce it to zero. Jim Elsey is a mechanical engineer who has focused on rotating equipment design and applications for the military and several large original equipment manufacturers for 48 years in most industrial markets around the world.
He is the general manager for Summit Pump Inc. Elsey may be reached at jim summitpump. Subscribe Now and Get: In-depth articles on pump industry issues Expert insights into important topics in the field Keep up with trends, basics, and more. Breadcrumbs You are here: Home. Why you should be worried about a few bubbles. Image 1. An outline of where classic cavitation occurs Image courtesy of the author. Read more Common Pumping Mistakes articles here.
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An in-depth look into rotating equipment—and industrial pumps in particular—with the aim to empower users to maximize efficiency. Sponsored by Voith. Revitalizing Retrofits for Pumps in Power Generation. When the liquid flow rates rise at the pump suction than at the designed case, frictional pressure drop level rises with the increasing flow rate.
This lowers the pressure increases the chances for cavitation to occur at the suction pump. Cavitation can be caused by a number of factors.
It is advisable to prevent pump impeller cavitation which occurs as a result of vaporization. Our expert team can answer and all questions you have! What is Cavitation and What Causes It Cavitation is the formation and collapsing of cavities or bubbles in a liquid mostly developed in the areas which have relatively low pressure around the pump impeller.
What causes it? Rapid dropping in the pressure at the suction nozzle The fluid pressure at the suction pump needs to be above the liquid vapor pressure. Unwanted flow conditions Sometimes obstructions in the valves and sharp elbows do occur.
Uneven increase of the pumped liquid temperature At certain times the temperature at of the liquid can rise unevenly. High fluid velocity at the suction pump When the liquid flow rates rise at the pump suction than at the designed case, frictional pressure drop level rises with the increasing flow rate.
Recent Crane Engineering News. Subscribe to News and Events. Equipment Maintenance Pumps Troubleshooting. Written by Sara Peters. March 31, Facebook LinkedIn Twitter Email. What is pump cavitation? Suction Cavitation When a pump is under low pressure or high vacuum conditions, suction cavitation occurs. Make sure it is running at its best efficiency point.
Running the pump off its best efficiency point not only causes excess recirculation, expect excessive heat, radial loads, vibration, high seal temperatures, and lowered efficiency. Re-evaluate pipe design - Ensure the path the liquid takes to get to and from your pump is ideal for the pump's operating conditions. Both result in suction problems and pump cavitation. Struggling with a cavitation problem? Ask us about it! We gladly provide technical assistance to businesses in Wisconsin, Minnesota, Iowa and Upper Michigan.
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