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.

--
Ed Huntress


This is a common question in the fire service. Now if the pump is rated
for a higher pressure and flow it could boost the pressure. That is how
a 2 stage high rise pump operates. Those may pull in 90 psi hydrant
water through a 5", feed that through the first stage and boost it to
125 psi. That is then fed into the second stage which can boost it to a
higher pressure. Our old two stage could put out 300 psi through a 4"
line. with 70 psi at the 5" inlet. BUT if the inlet pressure dropped the
outlet dropped much farther.

Currently our biggest pump can lift water 20' and put out 2,075 gpm at
150 psi and keep pumping that way until she runs out of fuel. That's
with 2 6" suction lines

--
Steve W.