End of Curve Operation requirement for Auto start pumps
End of Curve Operation requirement for Auto start pumps
(OP)
Hi
I would like to know that for all the AUTO START centrifugal pumps ( Open valve start up) , whether it should be designed for End of Curve operation? That is , NPSHR should be less than NPSHA even even at its end of curve. I am guided to select a vendor who can satisfy the above condition. We have two pumps ( 1 running + 1 standby) . If one pump trips the other pumps should come in line in auto. we have individual NRV for these pumps . When I should propose to the vendors that my requirement of a centrifugal pump should be designed for the End of curve operation where the NPSHR is less than NPSHA at its end of the curve. Can U please throw some light on this.
I would like to know that for all the AUTO START centrifugal pumps ( Open valve start up) , whether it should be designed for End of Curve operation? That is , NPSHR should be less than NPSHA even even at its end of curve. I am guided to select a vendor who can satisfy the above condition. We have two pumps ( 1 running + 1 standby) . If one pump trips the other pumps should come in line in auto. we have individual NRV for these pumps . When I should propose to the vendors that my requirement of a centrifugal pump should be designed for the End of curve operation where the NPSHR is less than NPSHA at its end of the curve. Can U please throw some light on this.





RE: End of Curve Operation requirement for Auto start pumps
If the pumps can not run to end of curve there is no need for the NPSHr to be less than the NPSHa - calling for this in a contract will only result in larger and more expensive pumps which will then run too far left of their BEP in normal operation.
However, if they can run to end of curve you need to look at the running period before they run up the H/Q curve to the normal operating point - a short period of cavitation is usually not a problem.
RE: End of Curve Operation requirement for Auto start pumps
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"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: End of Curve Operation requirement for Auto start pumps
Hi Biginch
I am not able to understand your answer of " add a high flow or low suction pressure shutdown" Pl explain
RE: End of Curve Operation requirement for Auto start pumps
If your system curve and pump curve can intersect at high end of curve flowrates, where suction pressures drop below NPSHr, BUT you don't need to pump those high flows, just install a low suction pressure switch, or a high flowrate switch to deavtivate the pump motor, or to control a VFD, or install a flow control valve to limit flows to acceptable ranges, where suction pressure is always higher than NPSHr.
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"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: End of Curve Operation requirement for Auto start pumps
Now I have understood Ur reply. But in my case , the duty point requirement / flows are well below the end of curve and have an NPSH margin more than 1 metre. Only that during initial start up of the pump, when the discharge lines are empty , whether this pump will go to its end of curve operation ? At this condition from the performance curve we see that the NPSHR at the end of curve is 7.5 M as against the avl NPSHA of 4 metres. Our concern is , during the pump start up ( by keeping discharge valve open) because it may operate upto its end of curve , should we ask the vendor to suggest a different model pump.
RE: End of Curve Operation requirement for Auto start pumps
Typically, you want a pump to start up against a closed valve, isn't that so? And in this particular case, you have a non-return valve, correct?
RE: End of Curve Operation requirement for Auto start pumps
**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: End of Curve Operation requirement for Auto start pumps
Johnny Pellin
RE: End of Curve Operation requirement for Auto start pumps
**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: End of Curve Operation requirement for Auto start pumps
RE: End of Curve Operation requirement for Auto start pumps
**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: End of Curve Operation requirement for Auto start pumps
Johnny Pellin