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Pump Low Discharge Pressure

09/10/2020 10:00 PM

The discharge pressure of a pump is lower than the calculated value of discharge pressure using the pump head. What could be the possible reasons?

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#1

Re: Pump Low Discharge Pressure

09/11/2020 12:45 AM

Suction air leak, obstruction, low voltage, miscalculation, pump not properly primed, loose impeller, bad gauge or blocked tube...

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#2
In reply to #1

Re: Pump Low Discharge Pressure

09/11/2020 1:00 AM

Don’t know what your pumping...

but if it’s water,

1.) there be a noticeable amount of encapsulated air in the water...

2.) also if there is air leak... you would hear the pump cavitation...

if it’s a wash cycle with detergent

1.) if it’s an air leak, same as above, but their be quite a lot of foam.

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#3
In reply to #1

Re: Pump Low Discharge Pressure

09/11/2020 3:09 AM

...a budgerigar stuck in the pump inlet, inadequate maintenance, electricity under-frequency and/or under-voltage, pipelines larger and/or shorter and/or smoother than the input figures to the calculation...

Is there a prize for getting the right answer?

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#4

Re: Pump Low Discharge Pressure

09/11/2020 3:12 AM

If the discharge pipe resistance is low, the pump will be operating relatively to the right on its curve, where the actual head is less than what the pump can produce under more restricted flow. There isn't necessarily anything wrong, as long as NPSHA is adequate.

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#5
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Re: Pump Low Discharge Pressure

09/11/2020 3:01 PM

..."NPSH stands for Net Positive Suction Head and is a measure of the pressure experienced by a fluid on the suction side of a centrifugal pump. It is quoted as a Head (in feet or metres) rather than as an actual pressure (lb/in2 , psi or Pa) because ‘head’ is a fluid-independent property: a pump will lift different fluids to the same height irrespective of their densities.

NPSH is defined as the total head of fluid at the centre line of the impeller less the fluid’s vapour pressure. The purpose of NPSH is to identify and avoid the operating conditions which lead to vaporisation of the fluid as it enters the pump – a condition known as flashing. In a centrifugal pump, the fluid’s pressure is at a minimum at the eye of the impeller. If the pressure here is below the vapour pressure of the fluid, bubbles are formed which pass on through the impeller vanes towards the discharge port. As the bubbles of vapour are transported into this higher pressure region, they can spontaneously collapse in a damaging process called cavitation (Figure 1). The repeated shock waves produced by this process can be a significant cause of wear and metal fatigue on impellers and pump cases. "...

https://www.michael-smith-engineers.co.uk/resources/useful-info/npsh

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#6
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Re: Pump Low Discharge Pressure

09/11/2020 4:55 PM

Almost EVERY answer you post is the result of a Google search, not, it seems, actual knowledge/experience.

At one time, Google only responses were frowned upon by Adim. but those days must be over.

Tornado has, over the years shown, his knowledge and expertise to be impeccable in many areas.

The jury's still out on you.

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#7
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Re: Pump Low Discharge Pressure

09/11/2020 8:00 PM

What?,... You believe that’s your job?... And now you proclaim the jury’s still out for SE,... so,... who gave you the promotion?

You’d pout that some posters don’t do their own search’s...

You were the master of google and that maybe the CR4 Admin didn’t frown upon that, they maybe just frowned upon you.

what is wrong with you? Or is it more like jealousy of someone that does your old job... better.

is that the response your looking for?

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#10
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Re: Pump Low Discharge Pressure

09/11/2020 11:17 PM

Don't put words in my mouth, or imagine that I said something that I never said! You are sometimes prone to misstate the truth.

Have a great life.

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#11
In reply to #10

Re: Pump Low Discharge Pressure

09/11/2020 11:32 PM

Don’t try to defend yourself with BS... you were the google master,... and I pointed out to you repeatedly...

as far as the only time a label of liar was bestowed on me is when I offended you or your cohorts with the Their own hypocrisy where their only defense is crying liar.
and btw,.. what SE does,... it’s called research, where SE is better than you at it... and that really bothers you. Get over it...

and secondly,... acting up is what you’re so good at. Or did you forget about that also?... btw, you’re (e)

it was so peaceful when your on you hiatus ventures.,... no garbage rants, and yet when every time you return, so does your vile garbage.

You are a real head case and I just point it out.

have a good day...

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#17
In reply to #11

Re: Pump Low Discharge Pressure

09/12/2020 9:52 AM

Now now, children. Play nicely.

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#18
In reply to #17

Re: Pump Low Discharge Pressure

09/12/2020 10:27 AM

Of course... I won’t have it any other way.

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#12
In reply to #6

Re: Pump Low Discharge Pressure

09/11/2020 11:44 PM

Maybe it's just that I reference my sources....

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#13
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Re: Pump Low Discharge Pressure

09/12/2020 12:14 AM

If I had to speculate,... it has nothing to do with your references,... You did something to people like that, and they just has an axe to grind...

As far as your research references,... whether its COVID or in this case pump issues, in college what we studied on processes,... I’d call rudimental understanding,... the most I learned was after I got out, with educating myself with textbooks or more classes (theoretical),... but mostly it was from practical experience gained by mitigating the problems that arise.

and I’ll breeze through your research for sometimes badly needed refresher... That’s why I subscribed...

And here on this thread Tornado gave a good theoretically what can happen, and rwilliams gave a practical mitigation.

and the rest of the posting,... is someone showing ruffled feathers... I just hope he doesn’t go nuclear with his political garbage.

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#20
In reply to #12

Re: Pump Low Discharge Pressure

09/17/2020 8:57 AM

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#21
In reply to #12

Re: Pump Low Discharge Pressure

09/17/2020 9:07 AM

Oh that's funny. You are now claiming to respect references. Have you referenced logical fallacies or a dictionary lately?

Speaking of references, what is the difference between an egotist and a narcissist?

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#14
In reply to #6

Re: Pump Low Discharge Pressure

09/12/2020 3:12 AM

"Knowing exactly the right thing to say,I said nothing." Mark Twain

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#16
In reply to #14

Re: Pump Low Discharge Pressure

09/12/2020 9:50 AM

Quite.

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#19
In reply to #14

Re: Pump Low Discharge Pressure

09/14/2020 6:32 PM

That explains it...

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#8

Re: Pump Low Discharge Pressure

09/11/2020 10:29 PM

As Tornado notes, if the actual head pressure is lower than calculated, it is likely there is a higher flow than design, and with it, a higher motor load. Not all pump motors are sized to deliver the maximum flow of a given pump, so if the pressure is significantly lower than design, check your motor load. Throttle the discharge to reduce the pump load, assuming a centrifugal pump, of course.

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#9
In reply to #8

Re: Pump Low Discharge Pressure

09/11/2020 10:45 PM

Nice follow up to tornado with a mitigation for a solution.

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#15

Re: Pump Low Discharge Pressure

09/12/2020 3:21 AM

What type of pump is it?How old is the pump?How old is the piping?Have you checked the dead-head pressure?

If a centrifugal pump,is it a submerged or above ground pump?

Is it a shallow well pump using two pipes,or a single pipe-within-a-pipe configuration?

A Centrifugal pump could have a partially clogged or damaged impeller or jet, or a worn diffuser ring.

More information will give better answers.

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#22

Re: Pump Low Discharge Pressure

09/21/2020 5:43 AM

Plot the head, flow and power on the pump curve and see which parameter does no fit. This will give you a good place to start your investigation.

Show us that plot and we can then propose problems/solutions.

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