Recirulation pump under performing

[flamearrow]

Hi Gents,

briefly, we got re circulation pump (D&S) (35 l/s 15.4m & SH-19m) for a tank capacity of 1500 cu.mtr with single suction & discharge (please find attached sketches. pump was giving 10 psi at discharge which was overlooked and modified the system to 8 suction &12 discharge as attached.
After tested, of course it has been found that field data not matched with manufacturer data.

crucial things is when the system reduced to very low profile as single suction and single discharge and pump was over sized, then why it gives low flow?

could anyone diagnose the actual error ( please be noted, velocity head and pressure gauges elevation also included in the calculations to obtain the tabulated results.
Thank you.

 

[LittleInch]

What is it your pumping and at what temperature / vapour pressure?

Only thing I can think of immeadiately is that your pump is cavitating badly.

Can you post the manufacturers curve as well please, not just the dots on the results chart.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[flamearrow]

Hi liitleInch,

Thanks for your reply

End suction centrifugal, pumping clean water with temperature not more than 35 deg C.(about & years of operation with single suction/discharge. Impeller pic attached, took after 6.5 years of operation.
Please find attached manufacturer curve, I would like to add that we have checked the rpm, running I/V in both condition and found constant as nameplate. And checked the impeller for cavitation and no sign of it. also no abnormal sound or vibration during operation.

 

[flamearrow]

Impeller pic attached. Pump has been running about 7 years, with single suction/discharge before modified to multi lines

 

[LittleInch]

Hmmm,

Not easy to say for definite where to go here. Data implies that pump may be suffering from years of low flow and either got damage to the internal vanes or seal leakage on the wear rings between discharge and suction side.

How accurate / how did you measure flow rate?

Anything stuck in the volute / discharge / suction inside of your pressure gauges?

Can only suggest you try a pump re-build and test it on a separate skid to see if you get the stated performance. 7 years operating at low flow won't have done it any good.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[flamearrow]

Pressure gauges are new, calibrated. did not find any noticeable clogs.

Flow measured with ultrasonic meter and later realized it might not be accurate if flow is low. then new calibrated turbine flow meter installed. Not much difference in the reading.

Impeller/ Volute checked, precipitated dirt cleaned and reassembled, but the result was same.

Do you believe the pump model is not appropriate e to the system, or what you could find from the pump-system curve?
Thank you

 

[flamearrow]

LittleInch

If other factors are normal, then possible reason for low flow will be from foot valves. foot valves might not open fully, means need to go for less stiff foot valves. What do you say?
Note that the foot valves used here PN-16 & 10.

 

[LittleInch]

Not easy to say from a distance, but all I can think is that you have some sort of internal pump re-circulation going on - hence the question about the wear rings or what the seal is between the inlet and outer parts of the internal working (items 4 and 5 of the cutaway of what I believe is your pump.

At a single system flow it looked like the pump was operating at minimum flow.

one thing - you have checked it's going the right way around have you? I mean actually you not someone else.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

Is the configuration of the field testing system similar to the original in the manufacturer shop?

The point is that, since the pump condition was cleaned and inspected without any issue, the problem could be resulted from the testing system, pipe, valves, instrumentation, etc.

 

[flamearrow]

Guys, thanks for the replies

Pump supplier suggests test bench testing, lets see

 

[LittleInch]

Be sure to come back and let us know what happens, even if it's in months time.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.