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In this multi-part series, we will investigate several aspects of centrifugal pump efficiency. First, I will define efficiency and give some examples. Next, I will examine some of the design criteria that ultimately dictate the efficiency exhibited by a particular pump.
There is no formula. Pump manufacturers test their pump by measuring at any given speed through the head (pressure) and volume range the amount of power consumed and compare this with the theoretical power required. This efficiency is not constant throughout the range. Generally manufacturers do not provide these efficiency points but do publish the expected power curve for any given pump speed.
Power is consumed by a pump, fan or compressor in order to move and increase the pressure of a fluid. The power requirement of the pump depends on a number of factors including the pump and motor efficiency, the differential pressure and the fluid density, viscosity and flow rate. This article provides relationships to determine the required pump power.
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It is for these reasons that an understanding of pump and motor efficiency can assist greatly in understanding and diagnosing issues with a hydraulic system. The three most considered efficiencies are volumetric efficiency, hydro-mechanical efficiency and total efficiency.
What Factors Affect The Efficiency of a Centrifugal Pump?
When we talk about the efficiency of a machine, we are basically referring to its capability to convert one form of energy to another. How well the machine does it becomes its efficiency. Let’s say we are supplying one unit of energy to a machine and its output is half unit, we say that the efficiency of the machine is 50 percent. The formula for calculating efficiency is (output-input) *100.
Submerged motor pumps (Fig 1) are widely used in the oil and gas industry for pumping cryogenic and low temperature fluids such as LNG, LPG, Ethylene, Ethane, Propane and Butane. SMPs use a pump and motor that are mounted on a common shaft and are immersed in the process liquid – either in the storage tank itself or in a suction pot as shown here.
Have you become so focused on the efficiency of the motors around your plant that you’re losing sight of the equipment those motors are driving? In many applications, pumps included, the answer to the efficiency question is best addressed when the complete system is studied.
Vertical centrifugal pumps
Volumetric efficiency of a pump (ηv) is defined as the ratio of the actual flow rate delivered by the pump to the theoretical flow rate (i.e., flow rate without any leakage) that must be produced by the pump.
Thanks for the explanation of 3960. I have one confusion. I HP=550 lbf-ft-sec, not lbm-ft-sec. And mass of 1 gallon of water=8.34 lbm. For getting 3960, you have to consider lbm=lbf, which is not correct.
Andrew Ondish is a District Sales Manager for Grundfos Pumps, Corp. He holds a BSc. in Petroleum Engineering and a MSc. in Organizational Leadership. His 20-year tenure in the pump industry includes product engineering for industrial pump applications.
Like looking for the Philosopher’s Stone in the Middle Ages or the Fountain of Youth in the 1600s, owners and operators of large machinery are always looking for better hydraulic efficiency for their hydraulic pumps and motors. Besides the obvious need to protect the moving parts in their machines via strong hydraulic fluids, there’s also the increased operational efficiencies to consider as well as the fewer repairs that come along with a maximized hydraulic fluids system. And of course there are many theories about the best way to go about getting this ultimate hydraulic efficiency.