Flow rate thru a 3' well point

mech4385October 23, 2004

Can anyone tell me how many gpm's a 36" well screen is capable of flowing . The local well supply specialist in my area tells me the limiting factor in a wells gpm is the strata which the point sits in and not the point,he tells me a 36" point is capable of at least 30 gpm , needless to say I dont believe him, anyone have any opinions? my well is producing about 11 gpm, I need 15 gpm to make my irrigation system function properly/ how about driving a second point & joining them w/ a manifold?. Also I have a 1 1/2 h.p. Goulds j15s pump that is supossedly capable of 17.6 gpms at a static water level of 10 ft. My static water level is 8 ft. How can I get the full 17.6 gpm's out of this pump?

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irri_guy(No CA)

Are you testing flow with open discharge from the pump? Or, at a higher, constant pressure? No implication you are mistaken, just that not all factors in total dynamic head are stated as yet. Centrifugal pump output is not a fixed number, it varies with the sum of lift, friction loss, and discharge pressure.

Since flow is below expectations, there is a possibility the drawdown level while pumping is quite a bit below the static level, maybe close to top of inlet. This too has the effect of increasing total dynamic head and reducing flow. The static level is just the starting level.

Lastly, what is the size and length of suction pipe, which contributes friction loss to the total. Same for discharge side, if it's long.

So,it would be helpful if you could describe your setup and exactly how you tested. You can download the "JS+ Bulletin" from Goulds if you want to see a table of pump output data.

Here is a link that might be useful: Goulds JS Plus

    Bookmark   October 24, 2004 at 12:42AM
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I am testing with a wide open piece of 1" poly pipe aprox 6' long attached to the discharge so I would assume the discharge pressure is probably 5 psi or lower. The suction side is about 18 ft in total length and it is 1 1/4 galvanized with a check valve approx 12 inches from the pump head, as I mentioned before static water level is approx 8 ft& doesnt appear to change much while pump is running ( well is cased so I can look at the static level while pump is running ). Using this setup I am filling a little more than 2- 5 gallon pails every minute. Also is it possible that the check valve is limiting my flow? It has an opening that is much smaller than the 1 1/4 galv pipe. thanx, Mech

    Bookmark   October 24, 2004 at 5:59AM
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11 GPM is pretty good for a single point. The strata is the key factor given you have a good static water level. You can always put smaller valves in your irrigation heads to compensate. Or, add another point. Did you properly develop the well after installing it?

    Bookmark   October 24, 2004 at 3:37PM
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I have already downsized the nozzles in my irrigation system to the minimum size jets that will effectively cover the lawn, 15 gpm is about as low as I can get it. Steve do you know if adding another well point to my system could possibly get my gpm up to at least 15gpm thanx / Eric

    Bookmark   October 24, 2004 at 6:59PM
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irri_guy(No CA)

You are testing flow essentially at open discharge (low pressure). Per the pump specs, it is capable of at least 25 gpm at very low discharge pressure.

You also report only slight drawdown from static level. That indicates the surrounding strata is not the limiting factor.

The above narrows the problem down to the suction system being too rerstrictive or the pump having an internal problem. That could be clogging with mineral buildup, more in the nonmoving components, or a damaged/very worn impeller.

I will hazard a guess that the problem is in the suction and the pump is okay. Is the pump noisy when running, sounding like gravel is going through? That indicates cavitation, which is forming and collapsing bubbles of water vapor. That in turn means starving for water, and it is damaging the pump over time.

If it's at all practical, you could set up a temporary, short , larger suction to a container of some sort to test the pump itself. I have not worked with this shallow well stuff, so I'm not up on the details of jet pumps, well points, etc. (Here, we tend to use submersibles in deeper wells and centrifugals out of surface water or tanks.) However, one rule of thumb calls for a suction velocity under 1.5-1.6 ft/sec in this size range.

That means 2 inch pipe for the desired flow. OR a couple of suction drops, preferably in 1 1/2 inch, manifolded together close to the pump. It is normal to use a suction a couple of sizes larger than the pump inlet, bushing down close to the pump. One last thing, suctions need to be plumbed so entrained air is not trapped in a high section before the pump inlet. That is, rising or level all the way to pump.

Assuming suction restriction is the problem, the question is whether to enlarge the entire single existing suction or add at least one more drop. Perhaps other informed folk will weigh in, always glad to learn something new.

    Bookmark   October 25, 2004 at 2:48AM
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Most homes here have shallow wells with sand points & jet pumps. Usual standard recomendation for our standard sand point is one 1.25 inch x four foot point per quarter horsepower.

My depth to water never changes and is 10 feet and with 1HP cheapo home depot jet pump and the pump reads 44psi for nozzled 17 gpm Hunter Rotors in the largest zone with minor pressure loss at heads(big pipes).

Pump, I removed built in 1.25" check replaced it with an enlarger and use a 1.5" suction manifold with a pvc flapper check about 18" from pumps intake.

Q&A from bradyproducts.com point manufacturer =
Q. What amount of water can I expect from a 1 1/4" well point?
A. Under ideal conditions, a Brady 1 1/4" well point can deliver between two to three gallons per minute per linear foot.

    Bookmark   October 25, 2004 at 5:27AM
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does anyone have any other opinions?

    Bookmark   April 12, 2005 at 9:18AM
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***Update**** Drove a second 1.25" x 3' point 5 feet away from first point & joined them together with a manifold. Pump now delivering approx 20 gpm's at 60 psi. I have so much water now that the pump started to cycle because the water pressure was building up to the cutout pressure (70 psi). Had to go back and install larger jets in my rotor heads to make system run properly. Waters entire one acre lawn now in 2/3 the time it used to take w/ better overlap of the heads resulting in more even coverage / Eric

    Bookmark   May 17, 2005 at 1:49PM
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    Bookmark   April 18, 2008 at 1:49PM
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