Centrifugal pump question

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
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On Friday, May 26, 2017 at 2:18:45 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

I think it depends on how much the flow is restricted. If you try to measure at the output of the pump and the water is just going into the air right at the output of the pump, then the pressure would be zero.
If you block the output of the pump I think it would be 90. So I think you could get zero to 90 , depending on how constricted the output is.
This is my guess.
Dan
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On Friday, May 26, 2017 at 2:48:20 PM UTC-4, snipped-for-privacy@krl.org wrote:

My guess is "no." The pump creates pressure from slinging a *mass* of water. I don't think it matters what the pressure is entering the pump.
--
Ed Huntress

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On Friday, May 26, 2017 at 3:39:34 PM UTC-4, snipped-for-privacy@gmail.com wrote:

To clarify that, I think that a typical 10 psi centrifugal pump that has 80 psi at the inlet will have something like 80 psi at the outlet.
--
Ed huntress

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snipped-for-privacy@gmail.com wrote on 5/26/2017 4:18 PM:

Why do you think there is something called "two-stage" or "dual-stage" air compressor?
The second stage will use the output of the first stage as its intake to add more pressure to it.
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On Saturday, May 27, 2017 at 8:17:29 PM UTC-4, rIOdE?? ? ??????? ? ?? ??????? ??UCAXF wrote:

measure at the output of the pump and the water is just going into the air right at the output of the pump, then the pressure would be zero.

nk you could get zero to 90 , depending on how constricted the output is.

water. I don't think it matters what the pressure is entering the pump.

s 80 psi at the inlet will have something like 80 psi at the outlet.

Because it has two stages.

With a gas, no problem. With a liquid, the problem is more complex.
--
Ed Huntress

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http://www.engineersedge.com/pumps/multi_stage_pump.htm
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Check Harbor Freight for a pump that boosts water pressure.
Hul
snipped-for-privacy@whidbey.com wrote:

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wrote:

I guess i could do that and see what kind of pump it is.
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On 05/26/2017 01:25 PM, snipped-for-privacy@whidbey.com wrote:

It would, but unless that pump is designed as a pressure-boosting pump, the likelihood of the shaft seal being able to contain such pressures is not high. On a cheap pump, even the housing might fail.
--
Bob Nichols AT comcast.net I am "RNichols42"

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snipped-for-privacy@whidbey.com wrote:

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.
This is a common question in the fire service. Now if the pump is rated for a higher pressure and flow it could boost the pressure. That is how a 2 stage high rise pump operates. Those may pull in 90 psi hydrant water through a 5", feed that through the first stage and boost it to 125 psi. That is then fed into the second stage which can boost it to a higher pressure. Our old two stage could put out 300 psi through a 4" line. with 70 psi at the 5" inlet. BUT if the inlet pressure dropped the outlet dropped much farther.
Currently our biggest pump can lift water 20' and put out 2,075 gpm at 150 psi and keep pumping that way until she runs out of fuel. That's with 2 6" suction lines
--
Steve W.

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On Saturday, May 27, 2017 at 2:26:40 PM UTC-4, Steve W. wrote:

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

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wrote:

That reference showed it could be done, but not how. I was hoping it would lead someone who knows more than I do about fluid dynamics to a better description.
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On Sat, 27 May 2017 12:20:00 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

The pumps in series business is confusing the issue. The output of the first (centrifugal) pump in the chain is far from an ideal pressure source. The original question was about a pump with a constant inlet pressure, either 0 psig or 80 psig. Flow wasn't specified, but as long as the flow is constant for both inlet conditions, the delta P across the pump will be the same. In other words, the pump will increase the pressure by 10 psi in both cases.
Consider connecting the pump to the bottom of a 180 foot tall (approx 80 psi head) tank. Will the pump be capable of pumping, at the specified flow, to a height of 23 feet (10 psi head) or 203 feet?
Practical matters of seal design aside.
--
Ned Simmons

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wrote:

Thanks Ned and everyone else who posted. I am going to put in a hot water recirculating setup in my house. I was going to buy the pump, valves, and pressure switch but I got lucky when a friend gave me a new Grundfos pump that was slated for in floor heating. I was pretty sure the pump would work but the Grundfos web site didn't mention what type of hot water circulating system it would work for. Eric
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On Saturday, May 27, 2017 at 6:57:12 PM UTC-4, Ned Simmons wrote:

e

0

ng

threw me. Since water isn't compressible, I don't see how the multi-stage p umps work. For gas, no problem, but I don't get it for liquids.

This is where I have trouble. Assuming these are regular centrifugal turbin es, the outlet of the first stage is fed into the axis of the second stage. The pressure from the first-stage outlet is retained at the second-stage i nlet, but from there it feeds into the whirling blades of the second stage, the outlet volume of which is LARGER than the inlet volume between any two blades.
Pressure, thus, is converted to velocity. Unless the machine *compounds* th e velocity at each stage, I don't see how it works. And, in order to compou nd velocity by a factor of, say, three, either the shaft driving the stage either has to be turning at (square root of 3) times that of the first stag e, or the the second stage has to have a completely different scroll design .
But you can carry that only so far. Go to three stages, or four, and the sh aft rotational speeds become outrageous, or the scroll design does.
Obviously, I'm missing something here, but I haven't yet seen what it is.
Ed Huntress

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wrote:

This is where I have trouble. Assuming these are regular centrifugal turbines, the outlet of the first stage is fed into the axis of the second stage. The pressure from the first-stage outlet is retained at the second-stage inlet, but from there it feeds into the whirling blades of the second stage, the outlet volume of which is LARGER than the inlet volume between any two blades.
Pressure, thus, is converted to velocity. Unless the machine *compounds* the velocity at each stage, I don't see how it works. And, in order to compound velocity by a factor of, say, three, either the shaft driving the stage either has to be turning at (square root of 3) times that of the first stage, or the the second stage has to have a completely different scroll design.
But you can carry that only so far. Go to three stages, or four, and the shaft rotational speeds become outrageous, or the scroll design does.
Obviously, I'm missing something here, but I haven't yet seen what it is.
Ed Huntress

==========================http://net.grundfos.com/doc/webnet/mining/_downloads/pump-handbook.pdf The pressure of a 10 meter head of water is close to one atmosphere. Section 3.2 describes pumps in series. Fig 3.2.5 and 3.2.6 show how the pressures add when the pumps are of equal or mismatched sizes. -jsw
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snipped-for-privacy@gmail.com wrote on 5/28/2017 11:35 AM:

A centrifuge pump creates pressure by spinning fluid away from the center (hence "centrifuge").
You are confusing yourself by of processing too much information at one time. To make it easy for you, let's consider the output valve is closed (the system is creating pressure but not expelling anything).
The first pump supplies the pressurized fluid to the second pump, the second pump spins the pressurized fluid away from the center to add more pressure to the housing wall. The pressure gauge in the second stage should register more pressure than the first stage.
Does this help you understand better now, Ed?
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On Sunday, May 28, 2017 at 12:43:23 PM UTC-4, lvCCL?? ? ??????? ? ?? ??????? ??IvVyG wrote:

?
be

10

ny

wing

ps threw me. Since water isn't compressible, I don't see how the multi-stag e pumps work. For gas, no problem, but I don't get it for liquids.

rbines, the outlet of the first stage is fed into the axis of the second st age. The pressure from the first-stage outlet is retained at the second-sta ge inlet, but from there it feeds into the whirling blades of the second st age, the outlet volume of which is LARGER than the inlet volume between any two blades.

* the velocity at each stage, I don't see how it works. And, in order to co mpound velocity by a factor of, say, three, either the shaft driving the st age either has to be turning at (square root of 3) times that of the first stage, or the the second stage has to have a completely different scroll de sign.

e shaft rotational speeds become outrageous, or the scroll design does.

s.

That's well said, but how is the fluid pressurized once it's fed into the s econd stage?
Take a look at the pump impellers in these photos:
https://www.google.com/search?q=pump+impeller&source=lnms&tbm=isch&sa =X&ved hUKEwjO8ceFk5PUAhWD7iYKHQCUBOYQ_AUICigB&biw20&bih4
(or, Tiny URL):
https://tinyurl.com/y9trhytf
Remember that the inlet is at the center of the impeller. The liquid then m akes a 90-deg. turn and enters the involutes. As the liquid travels from th e center to the periphery, the volume *increases*. Poof! There goes your pr essure out the window.
But I think I have it figured out now. The problem starts with the concept of "pressure." Except when you're dealing with gases, that's always problem atic. The physical measures that are involved here actually are mass, veloc ity, and force. Forget about pressure for a moment. Think energy instead.
If the previous stage can supply enough liquid to fill the subsequent invol ute more than it would be filled without that previous stage, then that sub sequent stage increases the energy of the water by increasing its velocity. "Pressure" is irrelevant. The energy going in is the product of mass and f orce (forget the actual formula for now). The energy coming out is the same thing, but along the way, an increase in velocity has increased the force. Restrict that mass and force at the pump exit, and you get pressure.
So that's what I think is happening.
--
Ed Huntress


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wrote:

That's well said, but how is the fluid pressurized once it's fed into the second stage?
Take a look at the pump impellers in these photos:
https://www.google.com/search?q=pump+impeller&source=lnms&tbm=isch&sa=X&ved hUKEwjO8ceFk5PUAhWD7iYKHQCUBOYQ_AUICigB&biw20&bih4
(or, Tiny URL):
https://tinyurl.com/y9trhytf
Remember that the inlet is at the center of the impeller. The liquid then makes a 90-deg. turn and enters the involutes. As the liquid travels from the center to the periphery, the volume *increases*. Poof! There goes your pressure out the window.
But I think I have it figured out now. The problem starts with the concept of "pressure." Except when you're dealing with gases, that's always problematic. The physical measures that are involved here actually are mass, velocity, and force. Forget about pressure for a moment. Think energy instead.
If the previous stage can supply enough liquid to fill the subsequent involute more than it would be filled without that previous stage, then that subsequent stage increases the energy of the water by increasing its velocity. "Pressure" is irrelevant. The energy going in is the product of mass and force (forget the actual formula for now). The energy coming out is the same thing, but along the way, an increase in velocity has increased the force. Restrict that mass and force at the pump exit, and you get pressure.
So that's what I think is happening.
--
Ed Huntress

If you can understand the steam injector then centrifugal pumps are
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