Pumps operating in end-of-curve
Pumps operating in end-of-curve
(OP)
Hi,
Here I have pumps selected for specified rated head and flow, but they are always operating in end-of-curve. There isn't any globe valve or control valve in discharge line to set specified rated flow.
For process, it's no problem because the service is water transfer from a basin to a tank.
But about pump and/or motor, can you see any problem for one of them?
Thanks
Rodrigo Alves
Here I have pumps selected for specified rated head and flow, but they are always operating in end-of-curve. There isn't any globe valve or control valve in discharge line to set specified rated flow.
For process, it's no problem because the service is water transfer from a basin to a tank.
But about pump and/or motor, can you see any problem for one of them?
Thanks
Rodrigo Alves





RE: Pumps operating in end-of-curve
The motor will also be affected as will your energy bill, by operating beyond the Best efficieny Point (BEP) and pumping at a much lower efficiency. It is likely that it is only because the motor is over sized for the rated duty, that it does not trip on excess amps. However temperature windings are probably at a higher temperature than they should be and hence may fail over time.
As you note, your system should include a retrofit of a control valve, either manual or actuated to keep the pump close to it's duty point for flow.
If you could post any more details such as the pump curve and where it operates plus some idea of size of pump and motor then that wpould be useful.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pumps operating in end-of-curve
RE: Pumps operating in end-of-curve
Surely not. The OP is asking for advise and to operate any machinery significnatly beyond its duty point will greatly increase the chance of premature failure. Cavitation is sometimes difficult to detect due to the noise of the motor and other machinery and may only occur at certain times such as low water level (I assume it's water). The motor may well be OK if was a standard size and has spare capacity, but the OP has not given any details of the pump and motor or curves or system description. What he really needs by the sound of it is a re-sized pump to match his system curve (motor is probably Ok), but some sort of throttling device is probably easier to install.
Rodrigo - what is your comment.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pumps operating in end-of-curve
RE: Pumps operating in end-of-curve
If your system is large, then you may have expensive failures and expensive costs to rectify. For a small system, the opposite.
How long has the system been in operation and why are you asking the question now?
Why was the system specified differently than it is operating?
Why would some recommend changes when the scope of the problem is not known?
RE: Pumps operating in end-of-curve
Johnny Pellin
RE: Pumps operating in end-of-curve
RE: Pumps operating in end-of-curve
We put an orifice plate in a flange down the discharge line. Not much restriction, just enough to move us back closer to BEP.
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Plymouth Tube
RE: Pumps operating in end-of-curve
Rodrigo - Do you have any feedback to offer us?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way