Two well pumps in series

[sowhatso]

Dear friends ,

I have a water well , 250m depth , with 10" casing, the allignment of the well is checked by 8" pipe , the pipe stucked at 170m, another allignment test is performed with 6" pipe and the pipe reached the bottom with no stuck. due to this bad result it is recomended to use a pump which has a daimeter less than 8".the flow capacity of the well is about 70m3/hr , with 190m head. and the pump setting is decided to be at 230-235m. I looked through many suppliers cataloges with no result of standard pump that can give the required operating condition due to the small size of pump diameter that can be used. Inaddition we will not use 3000rpm motor , only 1500rpm till 2000rpm. some people advised me to use two submersible pumps in series but I didnt use this type of installation before and I have no experience for the two pumps installation , can you help me with some of your advice or any precautions that I need to follow to install two pumps in series .

Thanks for all your input

 

[thewellguy]

Can some convert this for me and I find the pummp equipment he needs?

 

[vpl]

thewellguy

What conversion do you need? metric to American standard or vice versa? English language to some other language?

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[thewellguy]

Sorry, Gallons and feet

 

[Artisi]

Convert 70m3/hr to UG GPM x 4.4 = 308
190m to ft head x 3.28 = 623

 

[TenPenny]

If you want to stick with say 1800 rpm or less, you're going to need a 9 inch pump.

If a 9 inch pump won't fit, you'll have to accept 3000 or 3600 rpm.

You'll have to compromise.

Assuming you are in a 50 Hz electrical environment, there are 6" pumps that will do what you want at 3000 rpm, but you will also have to find a 6" motor to suit. And the pump will be something like 20 stages.

 

[Cheddarcaveman]

As has been stated, it is highly unlikely that you will get a pump of this diameter to meet this lift at 2000rpm.
Why can't you use a 3000rpm unit? Nobody is going to hear it 200m down the hole? Just get it, put it down at night time when nobody is watching, and watch all the smiles when the system works.

 

[sowhatso]

Dear friends ,

Does anyone of you have any experience regarding the installation of two pumps in series , I need some input and what things I should take care of it

 

[BigInch]

AS far as putting two in series down a well, no, but otherwise make sure the inlet pressure rating is equal to discharge pressure rating.

http://virtualpipeline.spaces.msn.com

 

[TenPenny]

I don't think that putting two pumps in series will accomplish anything for you. You have two constraints - you need to keep to about a 6 or 7 inch pump, and you want 1800 or 1500 rpm.

Let's assume you're in a 60Hz electrical environment, so your max desired speed is 1800 rpm. For a 7inch submersible, you are limited to about 350-400 gpm. Adding stages or pumps in series will do nothing to get you a higher flow.

That said, if you do, for some reason, want to put two submersible pumps in series, you will have to design casing to allow the water discharged from one pump to flow past the motor and into the suction of the second pump. You will be constrained by the physical space in the well and the size of the motor, along with the liquid velocity past the motor.

 

[Cheddarcaveman]

I ask again, WHY DO YOU NEED TWO PUMPS IN SERIES when one, higher speed pump will do? WHY CAN'T YOU RUN AT THE HIGHER SPEED???
There is no way you can physically "join" two 6" pumps in series down the hole (I don't think)!

 

[hydrae]

Chedder
If the client does not want 2 pole motors then the client does not want 2 pole motors.

As for a way to do this, take your first 6" pump and motor and install it normally with a 6" pipe riser, this riser would be span from 230 meters to 170 meters. at 170 m the a reducer would expand the pipe to 8" (some would call it an expander) and 10+/- meters of 8" pipe would be installed (the 8inch pipe still fits there). Inside the 8" pipe, the next 6" pump and motor is installed. the 8 inch pipe would extend beyond the 6" riser of the second pump. I would install a fail safe level switch inside the 8" to ensure the second pump has water to pump. I would also size the second pump to pump less water than the first pump so that some water would overflow out of the 8" pipe and back down the well. the 8 inch pipe would be welded to the 6" pipe with tabs, so the first pump is also supported by the drop pipe.

do-able, but worth it???

The control system would need extensive logic to ensure the safe operation of both pumps

Hydrae

 

[TenPenny]

hydrae, that's exactly what I was envisioning, but there's one thing you haven't mentioned: does anyone make a 6" submersible pump that will give you 600 gpm at 4Pole speeds?

Also, since the motor on a submersible pump is below the inlet, in your scenario, the inside of the 8" pipe will have a 6" motor in it; the 600 gpm is going to have to flow in the diametral space between the outside of a 6" motor and the inside of an 8" pipe.

That's not much space; what, about 22 square inches...600 gpm...that's a velocity of what, 533 ft/min????

 

[Artisi]

where does the 600 gpm come from?

 

[TenPenny]

600 gpm comes from what I was doing at the time...age, apparently, takes its toll. Windows can multitask poorly; some of us can multitask just as poorly.

The correct flow is, of course, 300 gpm or so.
So the velocity in question is what, 250 ft/min or so.

 

[EdStainless]

Yes, I have seen low head high volume pumps stacked. In the case that I worked on the pumps had about 500' of head and we needed about 900'. The upper pump was in a 'can' with standard pipe connections on both the inlet and outlet ends. The second pump was placed half way up the well, we tried to keep the pump loads balanced.
Controls are the killer with this system. You have to turn the lower pump on first and then just as it reaches shut in you turn the second pump on. Start too early and the second pump cavitates to death. Start too late and the bottom motor will burn up.
You also have to have very good restart protection. It will take a long time for the string to drain before you can turn the motors back on.

Tell them too get over the speed hangup. You don't have enough annular space for the canned upper pump. I used to build pumps, this unit is 11,000 BPD. Not small. It can be done at 3500rpm (60HZ) with a GN10000 and an 80hp motor.

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[thewellguy]

American Marsh/J-Line makes an 8EHC 1760 rpm bowl that will do 400 GPM and a 8MC thats closer to 300. Both are 8" sub turbine assemblies so I am sure that other manufactures make pump that will meet that conditions. I am have heard of this idea before, but I have never word of anyone doing it. I'm guessing you would have to use sub turbines and I am not sure how you would make that connections, but it thats what the customer wants thats what he gets. Just make sure you cover yourself on the warranty.

 

[Artisi]

TenPenny
" Windows can multitask poorly; some of us can multitask just as poorly."

I know how you feel