Can we guess a pressure of a centrifugal pump by it's head ? 3

[RuwanR]

I have one centrifugal pump in which the head is mentioned as 29 m .So the theoretical pressure according to the pressure should be 2.9 bar .But the actual pressure is 4 bar ? Can you please make me understand what is the difference....

 

[LittleInch]

This is really basic stuff here.

The head you mention is the differential head, i.e. the difference between the inlet and the outlet.
In your case it would appear that, assuming you're pumping water, the inlet pressure is approx. 1.1 barg.


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

 

[ashtree]

RuwanR

Little Inch could well be correct and this might be what is happening. You have not provided enough information to tell but if you are pumping from a tank that sits 10 metres above the pump or from a pipe with 100kpa of pressure than this is the case. However there could be another explanation as well.

Some pump manufacturers put a head rating on their pump nameplates which they see as the optimum or nominal. Flow is often quoted as well but the two ratings are not at the same point in the pumps rating curve.
So if your pump has on its nameplate 29m head but at the flow rate you are achieveing and the characteristics of what you are pumping into are such that the pump is developing 40 metres head than that is what is happening. However the flow rate will be much less than if the head was only 29 metres.
The pump ultimately develops the head required to push the fluid into the system to which is attached. If that system head is too high, the pump wont pump. If the system head is too low then the pump may overpump and will either meet its own hydraulic limits(only a certain amount of water can be pushed through a certain size outlet on the pump) or potentially the pump will cavitate and destroy the impeller.

Generally most systems operate somewhere between those two extremes and the pump and systems settle into some state of equilibrium in which as the flow increases the head increases until the pump's flow/head reaches a balance. In your case this would appear to be at 40 metres head.

See if you can find a rating curve for the pump and look at where the 29m and 40m head points lay along the curve. If you have a flow meter fitted you can than cross check against the flow.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[LittleInch]

True, I kind of assumed it was at the flow relevant to the 29m. Most centrifugal pumps operate in a region of +15%–10% head from rated duty, but each pump is different and some can be much more sensitive to flow. Remember head figures are all relative to the pump centre line.

More data needed!

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

 

[MortenA]

RuwanR,

As ashtree writes above, the nameplate capacity is but a single point un the pump curve. If your flow is less you head is higher and if its more its lower - thats just the way it is - unless you have variable speed. Also someone COULD have replaced the impellar - or the nameplate could be wrong.

So there is many possibilities. You do, however, have it right dP=dH*density*acceleration gravity - and if your head is in m and your fluid is water 29m==2.9 in DIFFERENTIAL pressure - so if your feed pressure is 1.1 barg then discharge would be 4 barg. So basically your question as infinite many possible answers (more or less ;-) )

Best regards, Morten

 

[RuwanR]

Thank you very much every one

 

[pumpingtips]

There are a couple of reasons why the head might be 40m. A slightly larger impeller diameter would do it (inside the same pump casing) A higher pump RPM would do it (probably unlikely if its direct coupled given that it is a high chance it is a water pump. As mentioned, a higher suction pressure would do it. A higher RPM can result if the pump was imported and the pump curve is for 50Hz electrical supply in the factory, but you are in USA for example at 60Hz field. And in each case the power draw would depend on the actual flow through the pump, and the pressure across the pump - TDH.
Oooroo