On Sat, 27 May 2017 12:20:00 -0700 (PDT), wrote:

On Saturday, May 27, 2017 at 2:26:40 PM UTC-4, Steve W. wrote:
wrote:
If a centrifugal pump with a maximum pressure of, say, 10 psi is
supplied with water at 80 psi will the water pressure coming out of
the pump be 90 psi? I think the pressure will be 90 psi. Am I wrong?
Thanks,
Eric

IF the volume of water remains constant the pressure coming out will be
at most 80 psi. if the pump is designed to produce 10 psi. It may be
lower depending on the size of the housing and the restriction the
impeller creates. Say your input side is 2" and the pump can produce 10
psi. at zero head pressure out of a 1.5" outlet.

Feed that pump with an 80 psi head pressure and the pump won't add any
pressure because it cannot pump faster than the water is already flowing
through it.

That's exactly what I thought, but Jim's reference to multi-stage pumps threw me. Since water isn't compressible, I don't see how the multi-stage pumps work. For gas, no problem, but I don't get it for liquids.

The pumps in series business is confusing the issue. The output of the
first (centrifugal) pump in the chain is far from an ideal pressure
source. The original question was about a pump with a constant inlet
pressure, either 0 psig or 80 psig. Flow wasn't specified, but as long
as the flow is constant for both inlet conditions, the delta P across
the pump will be the same. In other words, the pump will increase the
pressure by 10 psi in both cases.

Consider connecting the pump to the bottom of a 180 foot tall (approx
80 psi head) tank. Will the pump be capable of pumping, at the
specified flow, to a height of 23 feet (10 psi head) or 203 feet?

Practical matters of seal design aside.



--
Ned Simmons