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Submersible Pump Flow Discharge

07/18/2016 6:22 AM

A submersible pump used to pump the water.In the starting the flow speed is very fast but after 2-3 minitues the speed of the flow reduces.What could be the reason for reducing the flow speed?Can anyone guide?

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#1

Re: Submersible pump flow discharge

07/18/2016 6:38 AM

I am guessing that the pump is down a well or a bore.

If the pump is faster than the well replenishment capability, then the water level will drop.

As the water level drops, the pump has to lift the water higher and so the output reduces.

Do you know if the well capacity was considered when the pump was selected?

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#2
In reply to #1

Re: Submersible pump flow discharge

07/18/2016 7:08 AM

Yes it is down a bore well.Even though the water level is good it has same effect.

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#3

Re: Submersible pump flow discharge

07/18/2016 7:11 AM

Lift the pump about 2 to 3 feet and check. If result is same lower the pump and check.

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#4

Re: Submersible Pump Flow Discharge

07/18/2016 9:40 AM

If pump is setting on bottom or to close to it. It could be sucking up debrie that is clogging the suction strainer. Slowing down the flow. Which falls back off when the pump stops. Usually has a pulling rope supporting it off the bottom. Let it go slack then raise the pump two feet off the bottom.

You also could have a two or three stage pump. Drop in well level could be increasing head pressure so that the pump changes stages.

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#6
In reply to #4

Re: Submersible Pump Flow Discharge

07/18/2016 7:12 PM

I'm thinking the suction strainer too. I'm also curious to know if the OP checked the water clarity for sediments. A simple glass of water can tell a lot about what's going on in the system.

As usually, the forum needs more information.

"In the starting the flow speed is very fast but after 2-3 minitues the speed of the flow reduces."

How is this flow rate being measured? Flow meter, sight glass or by the pressure gauge? Anything other than a flow meter is anybody's guess as to what the actual flow rate is

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#5

Re: Submersible Pump Flow Discharge

07/18/2016 5:08 PM

In addition to losing your suction head, contamination being pulled up against your suction strainer/well point, as mentioned previously, you could also be increasing your discharge head or back pressure, pumping into an accumulator or tank with a air bladder in it. As the pressure builds up in your accumulator, your pump flow will drop.

If you are just pumping into a bucket up at ground level, vented, then the problem is at the suction.

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#7

Re: Submersible Pump Flow Discharge

07/19/2016 12:24 AM

As everyone else has said go back to basics on pumps.

Pumps deliver on a pump curve based on high flow low head and lower head at high flow. (You should have one for your pump but you can google them)

You start at one point (flow) and move to another lower flow this means (perhaps counter intuitively) the pump is delivering a higher head but not any flow so why

Higher suction drop ie the blocking of inlet strainers with cr&p from the well bottom

Higher back pressure from the delivery point

Higher pressure drop in the piping - if you are pumping cr&p into the discharge it will cause blockages in the piping.

The other problem with suction losses is that excess suction loss can cause cavitation - damage to the impeller and loss of performance.

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#8

Re: Submersible Pump Flow Discharge

07/19/2016 1:52 AM

For a submersible pump, the flow rate (not speed) and that would be measured in gallon per minute, m3 per day, or barrels per day, is VERY dependent on several things.

Number of stages or impellers in the pump.
Depth of the pump
Frequency of the power supply
The size of the tubing to surface.

Quick submersible pump lesson.. If one stage of a pump at 50Hz can lift (and this word LIFT is the operative word in submersible pumps) can lift a column of fluid to a height of 20 feet, how many stages do you need to lift fluid to surface from 100 feet?

The calculated answer is 5, but experience might say 6, but on calculating the 'Static fluid' and the 'Dynamic fluid' level, and the difference between them, you might only need 4 stages.
So you see there are several variables!
why am I stating all this? So you can understand the problems that might occur with ESP's.

(Static fluid level is the level the fluid reaches in the well when the pump is off, the dynamic fluid level is the fluid level when the pump is running. One would like to keep the DFL ABOVE the pump intake)

Now to cover your actual problem, the flow rate is depending on the Frequency of the supply (Laws of Affinity) LINK TDH - Total Dynamic Head, the losses in a system....

(What is dynamic head?
In fluid dynamics, Total Dynamic Head (TDH) is the total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. TDH = Static Height + Static Lift + Friction Loss. where: Static Height is the maximum height reached by the pipe after the pump (also known as the 'discharge head').)

The setting depth of the pump intake and the rate of flow coming from the source of the fluid in the well.

I'm guessing that your pump has little losses, not unless you have tubing to surface the diameter of a drinking straw, as you stated the flow rate is good for a few minutes, so the other possibilities are
1. A drop in power Frequency.. maybe
2.Your dynamic fluid level is at or just below the pump intake, so the pump is almost running dry. (this is my guess)

To check this.. get a clamp ammeter and place is on a power phase, start the pump and record the starting and stable current, then watch to see if the current drops as the flow rate decreases.
If it does, then your pump is to big for the well.
There are two options to correct this problem.....
1. install a valve at surface and close it slightly to reduce the flow, but keeping the flow rate constant and the current steady.
2. remove the pump and replace with a smaller one.

So first try the clamp meter to find out what the motor current is doing, and then work it out from there.

Now several folk have posted it might be sand and solids you are picking up... it could be.. to check this take a water sample in a clear glass bottle once the flow rate has dropped, and let it settle, if you see a huge amount of sand and crap in the water you can try and raise the pump up in the well. I hope you have not just dropped the pump into the well and it is indeed sitting at the bottom of the well.
Question.. what type of pump do you have.. does it have a bottom intake? Is there a screen at the bottom or on the intake?
Keep us all posted on your progress.

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#9
In reply to #8

Re: Submersible Pump Flow Discharge

07/19/2016 2:00 AM

The word for today is "gallimaufry". "Rigmarole" and "farrago" are other choices.

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#10
In reply to #9

Re: Submersible Pump Flow Discharge

07/19/2016 2:50 AM

That pretty well smokes out one person who is not knowledgeable about pump operation.

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#11

Re: Submersible Pump Flow Discharge

07/19/2016 4:08 AM

Does the discharge pipe drain when the pump stops, perhaps because there is no NRV, or it leaks? If so the pump will see lower head (hence higher flow) on start, head rising as the discharge pipe fills. 2 - 3 minutes seems a bit long if that is the reason, but worth checking.

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#12

Re: Submersible Pump Flow Discharge

07/20/2016 12:27 PM

Like my granddaddy, Will Stockdale, used to say,

( If'in it don't work, jess spit in the back, an' whomp it a good-un. It'll work ever' time...)

.

Well, I think that's whut he used to say...

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#13
In reply to #12

Re: Submersible Pump Flow Discharge

07/27/2016 1:39 PM

Well, does anybody else have ''No Time For Sergeants'' ? ...

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