Pump head question

breezy_moto said:

Trying to work through some pump problems as I've identified it as one of my weak points. For this question, from PPI Ch. 18, I'm confused on the head calculation in order to find Power. From the lake to the pump they only take into account the elevation head but not the friction head. According to the solution, total head = h elevation from lake to pump + h elevation pump to tank + h friction pump to tank. Can anyone shed some light? thanks.

https://photos.app.goo.gl/ZzeGTHmhucVsRUo32

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pat_in_the_hat said:

i have another pump question. not to hijack your thread but it seems you got your question answered

Question 138 in the NCEES latest practice exam.

They give inlet pressure (20-psig) of the pump. a discharge elevation (+160') and pipe friction loss (20'). And they are asking for the "minimum pressure rating (psi) of the piping system).

The way I did it was convert everything to psi, sum the elevation and friction loss since that is working against the pump, then subtract the inlet pressure (20psi) since this is helping the pump.

But the solution sums all 3 psi's together. 

Do they do this because they are asking for the pressure rating of the SYSTEM? I just feel like inlet pressure should be negative compared to elevation and friction

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Vel2018 said:

Question 138 in the 2016 NCEES which is the latest is about refrigeration. 

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breezy_moto said:

Not from what I see. I believe we're talking about the HVAC & R exam.

The inlet pressure is indeed helping the pump but that in turn adds to the pressure after the pump doesn't it? That's the way I looked at it.

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breezy_moto said:

Not from what I see. I believe we're talking about the HVAC & R exam.

The inlet pressure is indeed helping the pump but that in turn adds to the pressure after the pump doesn't it? That's the way I looked at it.

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