wrote on 5/29/2017 5:11 PM:
On Monday, May 29, 2017 at 5:01:14 PM UTC-4, LcISQwš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›nPkukO wrote:
Jim Wilkins wrote on 5/29/2017 2:30 PM:
wrote in message
...
On Sunday, May 28, 2017 at 9:23:49 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 2:17:58 AM UTC-4, HJART?? Mighty ?
Wannabe ??lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVx?? Mighty ?
Wannabe ??DiDrO wrote:
wrote on 5/27/2017 3:20 PM:
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.


Water is actually compressible. The compressed volume doesn't
change as
much as gas would.

"The low compressibility of non-gases, and of water in
particular, leads
to their often being assumed as incompressible. The low
compressibility
of water means that even in the deep oceans at 4 km depth,
where
pressures are 40 MPa, there is only a 1.8% decrease in volume."

https://en.wikipedia.org/wiki/Properties_of_water#Compressibility

Thanks. I suspect that most of the people here know that. The
pressure/volume relationship, though, isn't in agreement with
Boyle's law. Gases approximate it. It's easy to imagine a
multi-stage non-positive-displacement compressor that keeps
building pressure in a material that obeys Boyle's law. It's
much harder to imagine it with liquids.


The idea is the same. You use pressure to reduce the volume of a
fluid.
The gas/water restores it original volume after losing the
pressure.

I don't think so. Centrifugal pumps are very lossy machines. They
couldn't hold pressure that way.

From a physics point of view, I think the answer lies in sorting out
the kinetic aspects of a turbo pump (velocity) and the potential
aspects (pressure). A turbine pump that's pumping a liquid must be
producing potential energy from kinetic energy.

I'd need to see a good, expert explanation to understand it. I see
no way that an ordinary turbine pump can hold the pressure generated
by a previous stage, unless the entire thing is kinetic, which we're
then measuring as potential energy (pressure).


The graph in the link below shows that 200-bar of pressure (2900
psi)
will compress water by about 0.7% at 4�C (under STP, water is
1g/cc at 4�C):

http://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.html

No turbine pump could hold that 0.7% compression.

--
Ed Huntress

So what do you think happens if you have a centifical pump with a
pressure gauge on the output and the output blocked off so there is no
flow?

Dan
========================
That depends on the geometry of the impeller. A centrifugal fan may
stall, not couple as well to the air and draw -less- power. The
discharge curve gives the relationship between flow rate and pressure
rise.

A centrifugal pump is spinning the fluid 'round and 'round inside an
enclosed housing. It will never stall unless you feed solid debris like
straws and sticks into it.

A centrifugal pump is generating pressure by spinning the fluid to
generate centrifugal force. It is different from a turbo pump.

A centrifugal pump is a type of turbomachine.

https://en.wikipedia.org/wiki/Turbomachinery


"Turbomachinery, in mechanical engineering, describes machines that
transfer energy between a rotor and a fluid"

You are confusing yourself by reading too much and overloading your
brain, again.

The rotor in a turbine functions much like an electric fan or a ship's
propeller. It is designed to propel fluid in a direction perpendicular
to its plane of rotation.

On the other hand, the rotor (impeller) in a centrifugal pump is
throwing fluid radially outward parallel to its plane of rotation.

They are different in the principle they work. That's why one is called
a "turbo pump", the other is called "centrifugal pump", Ed.