On Sunday, May 28, 2017 at 7:09:22 PM UTC-4, tyre biter wrote:
On 5/28/2017 5:01 PM, wrote:
On Sunday, May 28, 2017 at 6:06:28 PM UTC-4, tyre biter wrote:
On 5/28/2017 3:59 PM, wrote:
After brushing up on impulse and momentum, and remembering that "pressure" is a frequently misleading term, I'm pretty sure I see what's happening.

-- Ed Huntress

Absolutely, your head is lodged in the toilet trap again, Crazy Eddy.

Poor biter. He must have really been stung when he found out he missed his IP geolocation "target" by over 20 miles.


LOL!

Oh eddy, crazy eddy...say his to the Tidi-bowl man for me woncha?

Nah, I wouldn't want to get between you and your co-workers, Biter.

--
Ed Huntress

On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4, wrote:



You are over thinking the situation. A multistage pump has a bunch of identical sections all turning at the same speed. Each stage increases the pressure. So you might have a 6 stage pump with each stage increasing the pressure by 10 psi. Which makes for a fairly efficient pump which will supply water at 60 psi. Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. At each stage, the fluid is directed to the center before making its way to the discharge on the outer diameter.

For higher pressures at the outlet, impellers can be connected in series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the boiler feedwater pump. For example, a 350 MW unit would require two feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical energy driving the impeller. This can be measured at isentropic compression, resulting in a slight temperature increase (in addition to the pressure increase)..



Dan

On May 28, 2017, wrote
(in ):

huge snip

I know how a centrifugal pump works. That video doesn't address the issue in
question: What happens when the input pressure is higher than the example in
your video? And how does it work?

Notice that you did not address the issue of the involute volume increasing
as the liquid flows from the center to the periphery, and the effect that has
on pressure.

I think that the missing piece is Bernoullis Equation:

..http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
..https://en.wikipedia.org/wiki/Bernoulli%27s_principle

For water (and air at low velocity compared to the speed of sound), read the
stuff about incompressible flow.

Joe Gwinn

On 5/28/2017 8:32 PM, wrote:
On Sunday, May 28, 2017 at 7:09:22 PM UTC-4, tyre biter wrote:
On 5/28/2017 5:01 PM, wrote:
On Sunday, May 28, 2017 at 6:06:28 PM UTC-4, tyre biter wrote:
On 5/28/2017 3:59 PM, wrote:
After brushing up on impulse and momentum, and remembering that "pressure" is a frequently misleading term, I'm pretty sure I see what's happening.

-- Ed Huntress

Absolutely, your head is lodged in the toilet trap again, Crazy Eddy.

Poor biter. He must have really been stung when he found out he missed his IP geolocation "target" by over 20 miles.


LOL!

Oh eddy, crazy eddy...say his to the Tidi-bowl man for me woncha?

Nah, I wouldn't

Oh well then, just blow him you usually do.

On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4, wrote:



You are over thinking the situation. A multistage pump has a bunch of identical sections all turning at the same speed. Each stage increases the pressure. So you might have a 6 stage pump with each stage increasing the pressure by 10 psi. Which makes for a fairly efficient pump which will supply water at 60 psi. Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. At each stage, the fluid is directed to the center before making its way to the discharge on the outer diameter.

For higher pressures at the outlet, impellers can be connected in series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the boiler feedwater pump. For example, a 350 MW unit would require two feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical energy driving the impeller. This can be measured at isentropic compression, resulting in a slight temperature increase (in addition to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few days.. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.

--
Ed Huntress

On Monday, May 29, 2017 at 11:37:30 AM UTC-4, tyre biter wrote:
On 5/28/2017 8:32 PM, wrote:
On Sunday, May 28, 2017 at 7:09:22 PM UTC-4, tyre biter wrote:
On 5/28/2017 5:01 PM, wrote:
On Sunday, May 28, 2017 at 6:06:28 PM UTC-4, tyre biter wrote:
On 5/28/2017 3:59 PM, wrote:
After brushing up on impulse and momentum, and remembering that "pressure" is a frequently misleading term, I'm pretty sure I see what's happening.

-- Ed Huntress

Absolutely, your head is lodged in the toilet trap again, Crazy Eddy.

Poor biter. He must have really been stung when he found out he missed his IP geolocation "target" by over 20 miles.


LOL!

Oh eddy, crazy eddy...say his to the Tidi-bowl man for me woncha?

Nah, I wouldn't want to get between you and your co-workers, Biter.

Oh well then, just blow him you usually do.

Like most of the trolling trash on the Internet, you ran out of gas and grabbed for homoerotic slurs before you said a single substantive thing.

Your brain must be the size of a pea, Biter.

--
Ed Huntress

On Monday, May 29, 2017 at 10:11:42 AM UTC-4, Joseph Gwinn wrote:
On May 28, 2017, wrote
(in ):

huge snip

I know how a centrifugal pump works. That video doesn't address the issue in
question: What happens when the input pressure is higher than the example in
your video? And how does it work?

Notice that you did not address the issue of the involute volume increasing
as the liquid flows from the center to the periphery, and the effect that has
on pressure.

I think that the missing piece is Bernoullis Equation:

.http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
.https://en.wikipedia.org/wiki/Bernoulli%27s_principle

For water (and air at low velocity compared to the speed of sound), read the
stuff about incompressible flow.

Joe Gwinn

Thanks, Joe. That is a good way to deal with the conversion and conservation of energy. If I can find out what the dynamics are inside of that second stage, it may help.

Without going into details, here's the basic dilemma. Note that the volume of the involutes increases as you progress from the center to the periphery.. Illustrations usually show that volume filled at the center, but only partly filled at the periphery. I don't know if the illustrations are correct or not. If they are, then there is no pressure involved inside of the involute -- only velocity and mass.

If they *are* correct, then the velocity must *decrease* as you progress from center to periphery, to conserve energy with the larger mass involved. That's the static view. It's possible that a dynamic view allows for both an increase in volume and an increase in velocity, due to the energy added by the rotation of the wheel.

I don't think that's what happens. I think it's a case of velocity increasing. If that's the case, the energy is imparted by the second stage by the velocity imparted by radial acceleration -- which is what we're often told is the way a centrifugal turbomachine works.

Now, if that's true, then what is the effect of feeding the second stage with water at high pressure? What happens with that pressure inside of the involute? It can't be conserved because, if the involute isn't filled, it's unconstrained and it simply fills up the empty volume near the periphery. Energy is conserved because the mass*velocity is conserved: greater mass, less velocity.

Is that what happens? I've found no explanation or illustration of it so far.

wrote in message
...
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4,
wrote:



You are over thinking the situation. A multistage pump has a
bunch of identical sections all turning at the same speed. Each
stage increases the pressure. So you might have a 6 stage pump
with each stage increasing the pressure by 10 psi. Which makes
for a fairly efficient pump which will supply water at 60 psi.
Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a
multistage centrifugal pump. The impellers may be mounted on the
same shaft or on different shafts. At each stage, the fluid is
directed to the center before making its way to the discharge on the
outer diameter.

For higher pressures at the outlet, impellers can be connected in
series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the
boiler feedwater pump. For example, a 350 MW unit would require two
feedpumps in parallel. Each feedpump is a multistage centrifugal
pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical
energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in addition
to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few
days. None of them really explain it. To say that the energy is
derived from the impeller is axiomatic. It doesn't explain what's
going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I
find a good explanation.

--
Ed Huntress
======

http://www.engineeringtoolbox.com/ve...ead-d_916.html

wrote on 5/29/2017 1:04 PM:
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4, wrote:



You are over thinking the situation. A multistage pump has a bunch of identical sections all turning at the same speed. Each stage increases the pressure. So you might have a 6 stage pump with each stage increasing the pressure by 10 psi. Which makes for a fairly efficient pump which will supply water at 60 psi. Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. At each stage, the fluid is directed to the center before making its way to the discharge on the outer diameter.

For higher pressures at the outlet, impellers can be connected in series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the boiler feedwater pump. For example, a 350 MW unit would require two feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical energy driving the impeller. This can be measured at isentropic compression, resulting in a slight temperature increase (in addition to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few days. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.


You don't have enough smarts to process too much information at once,
ED. Please do yourself a favour by looking at this impeller of a simple
centrifugal pump:

https://d2t1xqejof9utc.cloudfront.net/screenshots/pics/bd60670ae9dc5e37fdc08142df0462d2/large.JPG

To give your brain a chance to comprehend, please imagine all the valves
are closed. The fluid is trapped inside the centrifuge, with no way in,
and no way out.

The impeller keeps spinning 'round and 'round. The impeller is trying to
throw the fluid (which is slotted in the empty space in the impeller)
radially outward. Because of this, the fluid is exerting pressure
radially outward against the wall of the casing.

Do you still have difficulty, Ed?

On Monday, May 29, 2017 at 1:47:17 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4,
wrote:



You are over thinking the situation. A multistage pump has a
bunch of identical sections all turning at the same speed. Each
stage increases the pressure. So you might have a 6 stage pump
with each stage increasing the pressure by 10 psi. Which makes
for a fairly efficient pump which will supply water at 60 psi.
Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a
multistage centrifugal pump. The impellers may be mounted on the
same shaft or on different shafts. At each stage, the fluid is
directed to the center before making its way to the discharge on the
outer diameter.

For higher pressures at the outlet, impellers can be connected in
series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the
boiler feedwater pump. For example, a 350 MW unit would require two
feedpumps in parallel. Each feedpump is a multistage centrifugal
pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical
energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in addition
to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few
days. None of them really explain it. To say that the energy is
derived from the impeller is axiomatic. It doesn't explain what's
going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I
find a good explanation.

--
Ed Huntress
======

http://www.engineeringtoolbox.com/ve...ead-d_916.html

Thanks, Jim. That was one of the things I looked at. The problem with applying the formula for velocity head is that it assumes the flow is constricted (in a pipe, for example), while the expanding volume of a compressor involute presents an entirely different situation.

I'll bet I've read 100 pages over the past three days. g No joy yet.

--
Ed Huntress

On Monday, May 29, 2017 at 1:04:44 PM UTC-4, wrote:

u
Thanks, Dan. I read that -- and maybe 100 more pages over the past few days. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.

--
Ed Huntress

Try not to make it complicated. Say you have a centrifical pump rated at 5 gal per minute at 10 psi pressure. Well the pump when used really has a input pressure of about 14.7 psi. That is just atmospheric pressure. Now add a second pump with the same specs. Put the two pumps in parallel and you get 10 gal per minute at 10 psi output pressure. Put them in series and you have 5 gal per minute at 20 psi. It really does not depend on them being centrifical pumps. The same applies to gear pumps , turbine pumps, diaphragm pumps, etc.

What goes on in the second stage is exactly what goes on in the first stage..

Dan

On Monday, May 29, 2017 at 1:55:58 PM UTC-4, XCjEwCš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›CkYyoU wrote:
wrote on 5/29/2017 1:04 PM:
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4, wrote:



You are over thinking the situation. A multistage pump has a bunch of identical sections all turning at the same speed. Each stage increases the pressure. So you might have a 6 stage pump with each stage increasing the pressure by 10 psi. Which makes for a fairly efficient pump which will supply water at 60 psi. Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. At each stage, the fluid is directed to the center before making its way to the discharge on the outer diameter.

For higher pressures at the outlet, impellers can be connected in series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the boiler feedwater pump. For example, a 350 MW unit would require two feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical energy driving the impeller. This can be measured at isentropic compression, resulting in a slight temperature increase (in addition to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few days. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.


You don't have enough smarts to process too much information at once,
ED. Please do yourself a favour by looking at this impeller of a simple
centrifugal pump:

https://d2t1xqejof9utc.cloudfront.net/screenshots/pics/bd60670ae9dc5e37fdc08142df0462d2/large.JPG

To give your brain a chance to comprehend, please imagine all the valves
are closed. The fluid is trapped inside the centrifuge, with no way in,
and no way out.

The impeller keeps spinning 'round and 'round. The impeller is trying to
throw the fluid (which is slotted in the empty space in the impeller)
radially outward. Because of this, the fluid is exerting pressure
radially outward against the wall of the casing.

Do you still have difficulty, Ed?

Thanks, Wannabe, but I understand how a centrifugal pump works. What I don't understand is the effect of feeding one with a high pressure head of water.

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, HJARTš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVxš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›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

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.
https://mechanicalengineeringblag.wo...ckward-curved/
-jsw

wrote on 5/29/2017 2:03 PM:
On Monday, May 29, 2017 at 1:55:58 PM UTC-4, XCjEwCš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›CkYyoU wrote:
wrote on 5/29/2017 1:04 PM:
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4, wrote:



You are over thinking the situation. A multistage pump has a bunch of identical sections all turning at the same speed. Each stage increases the pressure. So you might have a 6 stage pump with each stage increasing the pressure by 10 psi. Which makes for a fairly efficient pump which will supply water at 60 psi. Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. At each stage, the fluid is directed to the center before making its way to the discharge on the outer diameter.

For higher pressures at the outlet, impellers can be connected in series. For higher flow output, impellers can be connected parallel.

A common application of the multistage centrifugal pump is the boiler feedwater pump. For example, a 350 MW unit would require two feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical energy driving the impeller. This can be measured at isentropic compression, resulting in a slight temperature increase (in addition to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past few days. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.


You don't have enough smarts to process too much information at once,
ED. Please do yourself a favour by looking at this impeller of a simple
centrifugal pump:

https://d2t1xqejof9utc.cloudfront.net/screenshots/pics/bd60670ae9dc5e37fdc08142df0462d2/large.JPG

To give your brain a chance to comprehend, please imagine all the valves
are closed. The fluid is trapped inside the centrifuge, with no way in,
and no way out.

The impeller keeps spinning 'round and 'round. The impeller is trying to
throw the fluid (which is slotted in the empty space in the impeller)
radially outward. Because of this, the fluid is exerting pressure
radially outward against the wall of the casing.

Do you still have difficulty, Ed?

Thanks, Wannabe, but I understand how a centrifugal pump works. What I don't understand is the effect of feeding one with a high pressure head of water.



It is the same. The pump doesn't know (and doesn't care) what's being
fed to it. It will spin and throw the fluid radially outward, resulting
in a higher pressure than it was fed. Imagine the output valve is
closed, in order not to complicate things.

wrote on 5/29/2017 2:03 PM:
On Monday, May 29, 2017 at 1:04:44 PM UTC-4, wrote:

u
Thanks, Dan. I read that -- and maybe 100 more pages over the past few days. None of them really explain it. To say that the energy is derived from the impeller is axiomatic. It doesn't explain what's going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I find a good explanation.

--
Ed Huntress

Try not to make it complicated. Say you have a centrifical pump rated at 5 gal per minute at 10 psi pressure. Well the pump when used really has a input pressure of about 14.7 psi. That is just atmospheric pressure. Now add a second pump with the same specs. Put the two pumps in parallel and you get 10 gal per minute at 10 psi output pressure. Put them in series and you have 5 gal per minute at 20 psi. It really does not depend on them being centrifical pumps. The same applies to gear pumps , turbine pumps, diaphragm pumps, etc.

What goes on in the second stage is exactly what goes on in the first stage.

Dan

A diaphragm pump may be a different story. The diaphragm in the second
stage or even further down the chain may not be able to handle the
pressure and then rupture.

Similarly, a piston pump may reach its pressure limit and either gets
stuck or breaks its push-rod.

A centrifugal pump is spinning the fluid in a closed system. As long as
the pressure doesn't burst the casing, then it doesn't really know or
care the pressure of the fluid it is spinning.

On Monday, May 29, 2017 at 2:10:17 PM UTC-4, wrote:
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, HJARTš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVxš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›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

You have static pressure. That, too, is axiomatic. But this is a dynamic machine.

--
Ed Huntress

On Monday, May 29, 2017 at 2:15:43 PM UTC-4, tyre biter wrote:
On 5/29/2017 11:18 AM, wrote:
On Monday, May 29, 2017 at 11:37:30 AM UTC-4, tyre biter wrote:
On 5/28/2017 8:32 PM, wrote:
On Sunday, May 28, 2017 at 7:09:22 PM UTC-4, tyre biter wrote:
On 5/28/2017 5:01 PM, wrote:
On Sunday, May 28, 2017 at 6:06:28 PM UTC-4, tyre biter wrote:
On 5/28/2017 3:59 PM, wrote:
After brushing up on impulse and momentum, and remembering that "pressure" is a frequently misleading term, I'm pretty sure I see what's happening.

-- Ed Huntress

Absolutely, your head is lodged in the toilet trap again, Crazy Eddy.

Poor biter. He must have really been stung when he found out he missed his IP geolocation "target" by over 20 miles.


LOL!

Oh eddy, crazy eddy...say his to the Tidi-bowl man for me woncha?

Nah, I wouldn't want to get between you and your co-workers, Biter.

Oh well then, just blow him you usually do.

Like most of the trolling trash on the Internet, you ran out of gas and grabbed for homoerotic slurs before you said a single substantive thing.

Your brain must be the size of a pea, Biter.

Oh I bet.

Right. Maybe a kidney bean.

--
Ed Huntress

On Monday, May 29, 2017 at 2:13:31 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 1:47:17 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 8:13:36 AM UTC-4, wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4, wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4,
wrote:



You are over thinking the situation. A multistage pump has a
bunch of identical sections all turning at the same speed. Each
stage increases the pressure. So you might have a 6 stage pump
with each stage increasing the pressure by 10 psi. Which makes
for a fairly efficient pump which will supply water at 60 psi.
Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a
multistage centrifugal pump. The impellers may be mounted on the
same shaft or on different shafts. At each stage, the fluid is
directed to the center before making its way to the discharge on
the
outer diameter.

For higher pressures at the outlet, impellers can be connected in
series. For higher flow output, impellers can be connected
parallel.

A common application of the multistage centrifugal pump is the
boiler feedwater pump. For example, a 350 MW unit would require
two
feedpumps in parallel. Each feedpump is a multistage centrifugal
pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the mechanical
energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in
addition
to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the past
few
days. None of them really explain it. To say that the energy is
derived from the impeller is axiomatic. It doesn't explain what's
going on inside the second stage.

Rather than try to go through it in detail, I'll post something if I
find a good explanation.

--
Ed Huntress
======

http://www.engineeringtoolbox.com/ve...ead-d_916.html

Thanks, Jim. That was one of the things I looked at. The problem with
applying the formula for velocity head is that it assumes the flow is
constricted (in a pipe, for example), while the expanding volume of a
compressor involute presents an entirely different situation.

I'll bet I've read 100 pages over the past three days. g No joy yet.

--
Ed Huntress

If the flow is unrestricted and just gushes out then it isn't
pressurized. If you want pressure you need to restrict the flow.
https://blog.craneengineering.net/ho...gal-pump-curve
"As pressure increases, the flow decreases moving your performance
point to the left of the curve. As pressure decreases, the performance
point runs out to the right of the curve and flow increases."
-jsw

Right. So what is the condition inside of one involute in the second stage? Is it completely full when it's operating?

--
Ed Huntress

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.

wrote on 5/29/2017 3:28 PM:
On Monday, May 29, 2017 at 2:10:17 PM UTC-4, wrote:
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, HJARTš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVxš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›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

You have static pressure. That, too, is axiomatic. But this is a dynamic machine.


You are talking nonsense. If you feed the output to storage tank, can
you tell the difference whether the storage tank is pressurized by a
turbo pump, a piston pump, a diaphragm pump, or a centrifugal pump?

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

--
Ed Huntress

On Monday, May 29, 2017 at 5:08:50 PM UTC-4, Dcbfddš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›tZsGTV wrote:
wrote on 5/29/2017 3:28 PM:
On Monday, May 29, 2017 at 2:10:17 PM UTC-4, wrote:
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, HJARTš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVxš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›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

You have static pressure. That, too, is axiomatic. But this is a dynamic machine.


You are talking nonsense. If you feed the output to storage tank, can
you tell the difference whether the storage tank is pressurized by a
turbo pump, a piston pump, a diaphragm pump, or a centrifugal pump?

My response to Dan's question is exactly correct. Static pressure cannot "feed the output" to anything. To "feed," it must be dynamic.

--
Ed Huntress

On Monday, May 29, 2017 at 3:34:50 PM UTC-4, wrote:
sw

Right. So what is the condition inside of one involute in the second stage? Is it completely full when it's operating?

--
Ed Huntress


It is exactly the same as the first stage.

Dan

On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

wrote on 5/29/2017 5:13 PM:
On Monday, May 29, 2017 at 5:08:50 PM UTC-4, Dcbfddš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›tZsGTV wrote:
wrote on 5/29/2017 3:28 PM:
On Monday, May 29, 2017 at 2:10:17 PM UTC-4, wrote:
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, HJARTš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›lBYWJ wrote:
wrote on 5/27/2017 11:08 PM:
On Saturday, May 27, 2017 at 8:28:04 PM UTC-4, dWuVxš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›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

You have static pressure. That, too, is axiomatic. But this is a dynamic machine.


You are talking nonsense. If you feed the output to storage tank, can
you tell the difference whether the storage tank is pressurized by a
turbo pump, a piston pump, a diaphragm pump, or a centrifugal pump?

My response to Dan's question is exactly correct. Static pressure cannot "feed the output" to anything. To "feed," it must be dynamic.


Think, Ed. If a centrifugal pump is registering 50 psi at the gauge
while the output valve is closed, what do you think the gauge at the
storage tank will register after it has been pressurized by the
centrifugal pump? It will be 50 psi, Ed. How is it different from any
other pump, Ed?

On Monday, May 29, 2017 at 5:13:41 PM UTC-4, wrote:
On Monday, May 29, 2017 at 3:34:50 PM UTC-4, wrote:
sw

Right. So what is the condition inside of one involute in the second stage? Is it completely full when it's operating?

--
Ed Huntress


It is exactly the same as the first stage.

Dan

And what is that condition? Are the involutes completely filled? And, if so, how is that possible unless the velocity is the same from the input port to the periphery of the wheel?

--
Ed Huntress

wrote in message
...
On Monday, May 29, 2017 at 2:13:31 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 1:47:17 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 8:13:36 AM UTC-4,
wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4,
wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4,

wrote:



You are over thinking the situation. A multistage pump has a
bunch of identical sections all turning at the same speed.
Each
stage increases the pressure. So you might have a 6 stage
pump
with each stage increasing the pressure by 10 psi. Which
makes
for a fairly efficient pump which will supply water at 60
psi.
Google it.


From Wik

Multistage centrifugal pumps
Multistage centrifugal pump[5]

A centrifugal pump containing two or more impellers is called a
multistage centrifugal pump. The impellers may be mounted on
the
same shaft or on different shafts. At each stage, the fluid is
directed to the center before making its way to the discharge
on
the
outer diameter.

For higher pressures at the outlet, impellers can be connected
in
series. For higher flow output, impellers can be connected
parallel.

A common application of the multistage centrifugal pump is the
boiler feedwater pump. For example, a 350 MW unit would require
two
feedpumps in parallel. Each feedpump is a multistage
centrifugal
pump producing 150 l/s at 21 MPa.

All energy transferred to the fluid is derived from the
mechanical
energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in
addition
to the pressure increase).



Dan

Thanks, Dan. I read that -- and maybe 100 more pages over the
past
few
days. None of them really explain it. To say that the energy is
derived from the impeller is axiomatic. It doesn't explain what's
going on inside the second stage.

Rather than try to go through it in detail, I'll post something
if I
find a good explanation.

--
Ed Huntress
======

http://www.engineeringtoolbox.com/ve...ead-d_916.html

Thanks, Jim. That was one of the things I looked at. The problem
with
applying the formula for velocity head is that it assumes the flow
is
constricted (in a pipe, for example), while the expanding volume of
a
compressor involute presents an entirely different situation.

I'll bet I've read 100 pages over the past three days. g No joy
yet.

--
Ed Huntress

If the flow is unrestricted and just gushes out then it isn't
pressurized. If you want pressure you need to restrict the flow.
https://blog.craneengineering.net/ho...gal-pump-curve
"As pressure increases, the flow decreases moving your performance
point to the left of the curve. As pressure decreases, the
performance
point runs out to the right of the curve and flow increases."
-jsw

Right. So what is the condition inside of one involute in the second
stage? Is it completely full when it's operating?

--
Ed Huntress

Why does that matter? The pump will force out all the air it can and
compress any that's trapped. If you want to build up pressure you have
to restrict the outlet, according to the discharge curve. The
Grundfoss manual showed that two identical stages will add their
pressures. Are you being distracted by imagining an improper mismatch?
-jsw

On Monday, May 29, 2017 at 5:31:58 PM UTC-4, tyre biter wrote:
On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

Ha-ha! What is there to fight? The blatherings of an imotent, cowardly weasel who is still suffering from the embarrassment of proclaiming my "location" that was in the wrong county and 20 miles away? You really can't let go, can you? And you don't have the wit to go anywhere, but you are worth a little low-rent entertainment.

Carry on, Biter. Let's see what's in the rest of your bag of slurs.

--
Ed Huntress

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.

On Monday, May 29, 2017 at 6:04:16 PM UTC-4, zzCjntš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›xPofsD wrote:
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"

Right. That's why I used the term.


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

I'm not overloaded. I'm trying to figure out the fluid dynamics within the involutes of a pump.


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.

No ****? g


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

If you're comfortable with your understanding of it, that's fine. I'm not comfortable with it. Something in the explanations is being oversimplified to the point where they make no sense.


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

They're both turbomachinery. In the context in which I used the term, it's correct. I was quite careful about how I used it.

--
Ed Huntress

On 5/29/2017 3:54 PM, wrote:
On Monday, May 29, 2017 at 5:31:58 PM UTC-4, tyre biter wrote:
On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

Ha-ha! What is there to fight?

Then why do you?

The blatherings of an imotent,{sic}

cowardly weasel who is still suffering from the embarrassment of proclaiming my "location" that was in the wrong county

And so you spnkd yourself, LOLOL!

and 20 miles away? You really can't let go, can you?

Crazy Eddy, you're the one in a lather, not moi...lol...

And you don't have the wit to go anywhere, but you are worth a little low-rent entertainment.

Yer largely trashed in your own froup - that's ****ing priceless!

Carry on, Biter. Let's see what's in the rest of your bag of slurs.

Beg me Crazy Eddy, beg for it!

wrote in message
...
On Monday, May 29, 2017 at 5:13:41 PM UTC-4, wrote:
On Monday, May 29, 2017 at 3:34:50 PM UTC-4,
wrote:
sw

Right. So what is the condition inside of one involute in the
second stage? Is it completely full when it's operating?

--
Ed Huntress


It is exactly the same as the first stage.

Dan

And what is that condition? Are the involutes completely filled?
And, if so, how is that possible unless the velocity is the same
from the input port to the periphery of the wheel?

--
Ed Huntress

How did you ever dream up that requirement? It isn't a positive
displacement pump. If the outlet valve is closed the input and output
velocities will be zero, yet the periphery is still spinning. The
pressure differential (p) from inlet to outlet will be what the
discharge curve shows for zero flow (q).
-jsw

On May 29, 2017, wrote
(in ):

On Monday, May 29, 2017 at 10:11:42 AM UTC-4, Joseph Gwinn wrote:
On May 28, 2017, wrote
(in ):

huge snip

I know how a centrifugal pump works. That video doesn't address the issue
in
question: What happens when the input pressure is higher than the example
in
your video? And how does it work?

Notice that you did not address the issue of the involute volume increasing
as the liquid flows from the center to the periphery, and the effect that
has
on pressure.

I think that the missing piece is Bernoullis Equation:

.http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
.https://en.wikipedia.org/wiki/Bernoulli%27s_principle

For water (and air at low velocity compared to the speed of sound), read the
stuff about incompressible flow.

Joe Gwinn

Thanks, Joe. That is a good way to deal with the conversion and conservation
of energy. If I can find out what the dynamics are inside of that second
stage, it may help.

Without going into details, here's the basic dilemma. Note that the volume of
the involutes increases as you progress from the center to the periphery.
Illustrations usually show that volume filled at the center, but only partly
filled at the periphery. I don't know if the illustrations are correct or
not. If they are, then there is no pressure involved inside of the involute
-- only velocity and mass.

If they *are* correct, then the velocity must *decrease* as you progress from
center to periphery, to conserve energy with the larger mass involved. That's
the static view. It's possible that a dynamic view allows for both an
increase in volume and an increase in velocity, due to the energy added by
the rotation of the wheel.
I don't think that's what happens. I think it's a case of velocity
increasing. If that's the case, the energy is imparted by the second stage by
the velocity imparted by radial acceleration -- which is what we're often
told is the way a centrifugal turbomachine works.

Model isnt quite right - water is incompessible, which means that the
volume of a package of water is constant - mass does not change either. And
Bernoullis equation is a direct consequence of the conservation of energy
applied to the flow of an incompressible fluid.

Now, if that's true, then what is the effect of feeding the second stage with
water at high pressure? What happens with that pressure inside of the
involute? It can't be conserved because, if the involute isn't filled, it's
unconstrained and it simply fills up the empty volume near the periphery.
Energy is conserved because the mass*velocity is conserved: greater mass,
less velocity.

Is that what happens? I've found no explanation or illustration of it so far.

Pumps in series do work, but the stages must be correctly matched for the
cascade to be effective. A good example is an axial-flow turbine - each fan
disk stage gives the passing fluid a kick (increases its velocity). If this
flow is impeded, the pressure will rise, until the stagnation (max) pressure
is reached.

If you look at the performance curve for any fan, it will be max flow at zero
head, and max head at zero flow, and max delivered aerodynamic power
somewhere between.

Id dig up a college intro to physics textbook and read the chapter about
Bernoullis equation. This will clarify the issue.

Joe Gwinn

wrote on 5/29/2017 6:14 PM:
On Monday, May 29, 2017 at 6:04:16 PM UTC-4, zzCjntš›†� ï¼*ｉｇｈｔｙ •¬ ï¼·ï½�ｎｎï½�ｂｅ †’š›xPofsD wrote:
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"

Right. That's why I used the term.


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

I'm not overloaded. I'm trying to figure out the fluid dynamics within the involutes of a pump.


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.

No ****? g


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

If you're comfortable with your understanding of it, that's fine. I'm not comfortable with it. Something in the explanations is being oversimplified to the point where they make no sense.


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

They're both turbomachinery. In the context in which I used the term, it's correct. I was quite careful about how I used it.


You are hopelessly thick.

Please look at this impeller of a centrifugal water pump. The fins are
acting like pedals, not blades. It is designed to throw fluid outward,
instead of pushing fluid forward.

http://www.iboats.com/mall/image/vendor/16/bigger/18-3087_big.jpg

Would you do us a favour? Please beat your head against the wall 10
times to clear your mind and then think again before you get back to us.

On Monday, May 29, 2017 at 6:21:04 PM UTC-4, tyre biter wrote:
On 5/29/2017 3:54 PM, wrote:
On Monday, May 29, 2017 at 5:31:58 PM UTC-4, tyre biter wrote:
On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

Ha-ha! What is there to fight?

Then why do you?

If I was fighting, weasel, you'd know it.


The blatherings of an imotent,{sic}

cowardly weasel who is still suffering from the embarrassment of proclaiming my "location" that was in the wrong county

And so you spnkd yourself, LOLOL!

I had to hold you by the hand because you were so sad and pathetic. And what does that do? Unlike you, I'm not a coward. I don't hide who I am.


and 20 miles away? You really can't let go, can you?

Crazy Eddy, you're the one in a lather, not moi...lol...

What lather, weasel?


And you don't have the wit to go anywhere, but you are worth a little low-rent entertainment.

Yer largely trashed in your own froup - that's ****ing priceless!

Trashed? What a moron you are.


Carry on, Biter. Let's see what's in the rest of your bag of slurs.

Beg me Crazy Eddy, beg for it!

You're on your own, weasel. Don't drown in your own drool.

--
Ed Huntress

On Monday, May 29, 2017 at 6:21:59 PM UTC-4, Jim Wilkins wrote:
wrote in message
...
On Monday, May 29, 2017 at 5:13:41 PM UTC-4, wrote:
On Monday, May 29, 2017 at 3:34:50 PM UTC-4,
wrote:
sw

Right. So what is the condition inside of one involute in the
second stage? Is it completely full when it's operating?

--
Ed Huntress


It is exactly the same as the first stage.

Dan

And what is that condition? Are the involutes completely filled?
And, if so, how is that possible unless the velocity is the same
from the input port to the periphery of the wheel?

--
Ed Huntress

How did you ever dream up that requirement?

Because if they are not completely filled, there is no physical way to transit any positive pressure at the inlet to the outlet. My further reading suggests they are filled, although some illustrations show them partly filled.. Photos taken through transparent windows show them partly filled, but those are illustrations of cavitation. I'm reaching the conclusion that they're completely filled in normal operation.

It isn't a positive
displacement pump. If the outlet valve is closed the input and output
velocities will be zero, yet the periphery is still spinning. The
pressure differential (p) from inlet to outlet will be what the
discharge curve shows for zero flow (q).
-jsw

If there is no flow, there will be no pressure differential. Pressure will be the same throughout the volume of liquid from inlet to outlet.

--
Ed Huntress

On Monday, May 29, 2017 at 5:37:34 PM UTC-4, wrote:
On Monday, May 29, 2017 at 5:13:41 PM UTC-4, wrote:
On Monday, May 29, 2017 at 3:34:50 PM UTC-4, wrote:
sw

Right. So what is the condition inside of one involute in the second stage? Is it completely full when it's operating?

--
Ed Huntress


It is exactly the same as the first stage.

Dan

And what is that condition? Are the involutes completely filled? And, if so, how is that possible unless the velocity is the same from the input port to the periphery of the wheel?

--
Ed Huntress

First some centrifugal pumps do not have involutes.

Second are you thinking there could be air in the pump? THa woud be bad as you would have cavitation.

The pump would be completely filled. How could it not be completely filled? And why would the velocity have to be the same from input port to the periphery?

The flow would be the same, but the passages vary in cross section, so there is no way the velocity could be the same.

Dan

On 5/29/2017 5:12 PM, wrote:
On Monday, May 29, 2017 at 6:21:04 PM UTC-4, tyre biter wrote:
On 5/29/2017 3:54 PM, wrote:
On Monday, May 29, 2017 at 5:31:58 PM UTC-4, tyre biter wrote:
On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

Ha-ha! What is there to fight?

Then why do you?

If I was fighting, weasel, you'd know it.

Oh Crazy Eddy, you sound so faux manly all of a sudden...


The blatherings of an imotent,{sic}

cowardly weasel who is still suffering from the embarrassment of proclaiming my "location" that was in the wrong county

And so you spnkd yourself, LOLOL!

I had to hold you by the hand because

Self-spank!

LOL.


and 20 miles away? You really can't let go, can you?

Crazy Eddy, you're the one in a lather, not moi...lol...

What lather, weasel?

This lather, Crazy Eddy.


And you don't have the wit to go anywhere, but you are worth a little low-rent entertainment.

Yer largely trashed in your own froup - that's ****ing priceless!

Trashed?

Oh boy am I LOVING IT too!

Carry on, Biter. Let's see what's in the rest of your bag of slurs.

Beg me Crazy Eddy, beg for it!

You're on your own, weasel. Don't drown in your own drool.


Beg me Crazy Eddy...do it...NOW!

On Monday, May 29, 2017 at 7:27:02 PM UTC-4, tyre biter wrote:
On 5/29/2017 5:12 PM, wrote:
On Monday, May 29, 2017 at 6:21:04 PM UTC-4, tyre biter wrote:
On 5/29/2017 3:54 PM, wrote:
On Monday, May 29, 2017 at 5:31:58 PM UTC-4, tyre biter wrote:
On 5/29/2017 1:32 PM, wrote:
Your brain must be the size of a pea, Biter.

Your pallid attempts at fighting back are hilarity, crazy eddy.

Ha-ha! What is there to fight?

Then why do you?

If I was fighting, weasel, you'd know it.



You're on your own, weasel. Don't drown in your own drool.


Beg me Crazy Eddy...do it...NOW!

What a trashy, low-class troll you are.

--
Ed Huntress