pump drawing low amps 1

[cams1975]

Hi

Please can you help, i have a 1 ph 240v heating pump.
The full load current is 2.7 amps however its only drawing 1.9 amps. I also dont get the correct differential accross the pump, the measured pressure is lower than the design.

Please can you advise where is should be looking in order to resolve the situation.

Regards

 

[EdStainless]

Is it pumping at all? sounds dead headed to me.
If it was 3ph I would suggest that it was running backwards.

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Plymouth Tube

 

[DRWeig]

Hi Cams,

Might be as simple as that the pump was designed with a bit of safety factor?

You'll never see a pump motor loaded to full load amps on the nameplate...

If you can give more specifics -- are you getting insufficient flow, for example, perhaps give us a diagram, the purpose of the pumping loop, etc...

Best to you,

Goober Dave

 

[cams1975]

Hi

the design duty was 1.9 l/s@ 70 kpa. The actual site measuremnts are 1.51 l/s@ 65 kpa and drawing 1.9 amps

regards

 

[zdas04]

Power draw is a function of flow rate and head. Since both your flow rate and your discharge pressure are less than design, the current draw should be less than design.

I guess the more interesting question is why the flow rate is less than design. That could be something as simple as suction pressure is less than design or as complex as scale on control surfaces. Without knowing the suction pressure near the eye of the impeller it is pretty pointless to speculate.

David

 

[JJPellin]

Perhaps this is a stupid question. What type of pump is it? Centrifugal? Gear? Flexible vane? It makes a big difference. We seem to be assuming it is centrifugal. But I didn't see anything that convinces me that is the case.

Johnny Pellin

 

[cams1975]

Its a centrifugal pump

 

[miningman]

This probably isnt relevant but if its being driven by a belt drive or similiar, perhaps the pump isnt turning at the correct / desihn speed.

 

[Artisi]

How is the flow and head measured and how accurate are the measurements - if accurate and flow and head are as stated, I would be looking at the inlet side of the system to start with - the problem could be either, air leakage or restricted flow.

To really sort out the problem you need to measure the head across the pump from inlet to outlet - at the moment you don't have any idea what is happening on the inlet side - you could be incuring a high inlet head loss.

 

[dabluffrat]

Do you have a pump curve? what should the rated pump BHP be compared to motor HP? You're still about 70% FLA at 1.9 A. Check for blockage at the suction/inlet as suggested, the pump may be starved (low NPSHa) and running off the end of the curve. If you have a discharge valve, try throttling the pump back on the curve.... record amps, then open at various settings (25% open, 50% open, 100% if you can, etc) and record amps. If the pump horsepower curve is continuously rising towards higher flows, amp draw should also increase as the valve is opened. If amp draw decreases as you open the valve, and discharge pressure decreases signifigantly, then suction pressure is likely too low

Did you know that 76.4% of all statistics are made up...

 

[ScottyUK]

Measuring line current is a lousy way to determine motor power, especially as the load drops. Use a power meter, not an ammeter. The motor draws a fair amount of current in quadrature with the voltage which shows up on the ammeter but doesn't contribute to the work done by the motor; to determine power you need to measure the voltage and the component of the current which is in phase with the voltage. You can't do that with an ammeter.


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If we learn from our mistakes I'm getting a great education!

 

[wimple]

the pump is still running in 80% of BEP. Looks like rated case coincide with BEP, if so there is nothing strange