Make Shortcut to Home Screen? Internal Losses hydraulic loss - due to disk friction in the impeller, rapid change in flow directions and velocity changes throughout the pump volumetric loss - due to internal re-circulation caused by wear in rings and bushes External Losses mechanical loss - due to friction in seals and bearings BEP - Best Efficiency Point The maximum efficiency for a pump is normally in its "design point" - also called BEP - or the "Best Efficiency Point" For pumps operating in all other positions - the efficiency will be less than in BEP.
Privacy We don't collect information from our users. Citation This page can be cited as Engineering ToolBox, Modify access date. Scientific Online Calculator. Pumps that have a single-volute casing design normally experience a rapid increase in impeller radial and thrust loads as the flow declines below BEP flow.
Dual-volute casing designs help to balance radial loads and are essential for reliability when a pump must operate for a substantial period of time at flows considerably below its BEP flowrate.
Modified concentric volute-casing designs are an alternative to single volutes — offering reduced radial loads in off-BEP operation, but giving up a little bit of pump efficiency in the process. The impeller loads that develop during off-BEP operation can lead to shaft deflection and mechanical seal failures, or overload the bearings with increased temperatures.
Figure 2. Cavitation can be created for demonstration purposes using a venturi. Discharge and suction recirculation happens when fluid does not flow through the pump as it was designed, causing small flow instabilities called eddies.
The damage caused by eddies mirrors cavitation and can lead to catastrophic pump failure when portions of the impeller inlet or discharge vanes fatigue and fail by breaking off. Temperature rise is one of the more severe effects of off-BEP operation, because at its most extreme, human life can be lost. Such explosions have been known to throw motors through concrete block walls. The chances of this happening are remote, yet real.
In pursuit of peak efficiencies and increased reliability longer mean time between failures , pump adjustments are often made to align their BEP with the duty point of the pumping systems. Excessive vibration can occur when pumps operate too far to the right of BEP, due in part to cavitation which causes hydraulic imbalances within the impeller as voids are formed by the vaporization of the liquid.
Excessive vibration can also occur due to higher bearing loads associated with pump operation closer to run-out or shut-off conditions. Impeller Damage can be caused by cavitation, and excessive vibration could potentially cause the rotor to make contact with the casing.
As the vapor bubbles, formed during the onset of cavitation, migrate to the higher pressure regions of the impeller, they implode with enough force to send shock waves to the surrounding area which in turn breaks molecules from the parent metal, leaving behind the telltale signs of cavitation — pitting and erosion.
This phenomenon can cause significant instability and can reduce flow. The damage caused by suction or discharge recirculation resembles cavitation and can lead to catastrophic failure of the pump when portions of the impeller inlet or discharge vanes fatigue and fail by breaking off. Reduced Bearing and Seal Life can occur as a result of recirculation and cavitation and will increase the maintenance costs as these components will need to be frequently replaced.
The rotor instability that occurs at off-BEP operation can lead to shaft failures, premature packing wear, mechanical seal failures, or simply higher bearing temperatures leading to premature lubrication breakdown. In our quest for higher efficiencies and increased reliability resulting in longer mean-time-between-failure, we often make modifications to the existing pumps so we can get their BEP to coincide with the duty point of the pumping systems.
Consider getting a certified performance test, from shut-off to run-out, to identify the BEP for your pumps. Improving efficiency by developing pumps for higher temperature systems The technology to exploit renewable energy sources is continuing to advance, improving…. Water is such a fundamental necessity for life that it is often taken for granted.
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