Pump Deadhead and Elevation

[Chance17]

I have a pump question - somewhat embarrased to ask -- but I can't get a clear model in my mind.
What is is the relationship between a pump being deadhead and discharge pipe elevation?

Assume a centrifugal pump moving water out of a tank with level 10-ft above suction elevation.
Assume the suction and discharge pipe are large so that friction loss is low.
Assume the discharge head is 200-ft.
Assume a pressure gauge installed on the discharge line at 120-ft elevation.
The pressure gauge should read 200+10-120 = 90-ft.

Now assume there is a block valve just down stream of the pressure gauge.
Assume the block valve is shut.
The pump discharge head moves to 300-ft
Question: Does the gauge also read 300-ft ??
or does the gauge read 300+10-120 = 190-ft ??

At deadhead, what is the impact of elevation ??

 

[BigInch]

The gauge does indeed read the pressure equivalent of 300+10-120 = 190 ft.

At deadhead, using the method you've used, which by the way is using a default reference elevation equal to the pump centerline elevation, is no effect.

If you were to use a reference elevation of say nearest mean sea level, you would have a different equation, but still get the same answer.

Pump elevation is 1000 feet msl and the other dimensions remain the same...

therefore the equation is,

(1000+300) + (1000 + 10) - 120 = (1000 + 190)
You can see by simply subtracting the reference elevation from all terms, the equation is different, but nontheless equivalent, showing you can use whatever reference elevation is convenient.

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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)

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