NPSHR Test
NPSHR Test
(OP)
In NPSHR tests, when a suction valve is piched down to reduce NPSH, the pump flow is of course reduced accordingly. How can they keep the flow unchanged ? The 3% drop-off curves are for constant flow and speed.
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RE: NPSHR Test
RE: NPSHR Test
If they have to open the discharge valve in order to return to original flow, I do not think they can get many data points of NPSH for a constant flow rate. Do they experience some limitations on the number of points available? How about changing the static lift instead of modulating suction valve?
RE: NPSHR Test
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: NPSHR Test
RE: NPSHR Test
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: NPSHR Test
RE: NPSHR Test
You must have some method of flow contol whatever it may be, such being able to hold flow while you reduce the suction head at the pump.
The suction piping for example can be designed such that, as you lower the inlet pressure into the suction piping from the source, and as you lower the suction piping outlet pressure (the inlet pressure into the pump), flow in the suction piping remains constant. To do that you must hold the suction piping's differential pressure constant (suction piping inlet pressure - suction piping outlet pressure). That will hold flowrate in the suction piping constant and send that into the pump, even as the suction head into the pump is also lowered. You want to be able to do that for all the flowrates you want to check.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: NPSHR Test
1) A pump is running at flow(A) and speed(B) with TDH(C).
2) When the suction valve is piched down a little bit to reduce NPSH, the pump TDH will be rising a little bit because of reduced flow.
3) By opening the second valve (either another suction valve or a discharge valve), the flow will be recovered to flow(A) with TDH(C).
4) Repeat 2) and 3) until 97% of TDH(C) is obtained.
5) Calculate NPSHA at 4), and it becomes NPSHR of the pump for flow(A), speed(B).
6) Repeat 1) to 5) for each flow and speed in the operating range.
Am I thinking correctly?
RE: NPSHR Test
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: NPSHR Test
So, to change the NPSHa to simulate different conditions (without changing any suction or discharge valve positions), you raise the tank up or down from its baseline point. If the flex hose is the same length, and the resulting bends as the tank moves are not too extreme, then the flow resistance remains about the same -> so the flow "should" remain about the same.
Or: use a pressurized tank, and change the air pressure above the tank to simulate different NPSHa values. Then a flowmeter in the suction can tell you the impact on higher or lower pressures on flow as well. After all, I understand that you want to find out the pump flow changes as suction pressure changes, not on how water inlet flow changes based on tank pressure.
RE: NPSHR Test
There are a number of ways to do this, just pick the easiest for you.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: NPSHR Test
Did you know that 76.4% of all statistics are made up...