Managing well overpumping

[Frank Spurlock]

I recently replaced the 25 yo 1/2 hp submersible pump in my 38 ft deep 4 inch well. The new Goulds 10GS05 pump was placed at 34 ft depth (same as old); the water level was 27 ft. I also installed a new Franklin QD control box. The 230 Volt pump motor is a Centipro. The new pump overpumps the well, and sucking air sounds occur followed by motor thermal overload tripping approx 30 seconds after startup. The pump distributor guy suggested installing a brass ball valve and partially closing the valve to increase effective head on the pump and reducing discharge. I did this. Before the the ball valve install, the pump motor was drawing 6.3A (above SFA) at well head pressure of 40 psi,corresponding to a Total Dynamic Head at pump of 27 feet +40*2.3 = approx. 120 feet by my calcs. I determined the approximate desired pressure at the well head by (1) selecting 10 GPM as the desired discharge (center of discharge curve = approx design discharge for the 10GS05), (2) determining the corresponding Total Dynamic Head of 180 from the Goulds pump discharge curve, and (3) backcalculating the desired well head pressure of approximately 66 PSI. I adjusted the ball valve accordingly, and seem to achieved the desired flow rate since my pressure tank 30 cut-in/50 cut-out drawdown volume of 27 gallons is refilled in about 2.5 minutes and everything seems okay so far. Oh, I also installed a pump-tec 231-insider pumpsaver for overpump/deadhead protection of the pump.

I have 2 questions:
1. Given that I really don't want to replace the incorrectly sized pump, does this all seem a reasonable way of managing the overpumping problem?
2. The pump motor current draw at the circuit box as measured by a clamp-on ammeter is 5.9 A for the 70 psi well-head back pressure ball valve setting. This lies between the Centipro motor FLA and SFA specifications of 5.3A and 6.1A, respectively. I don't really understand FLA and SFA very well. The pump distributor guy seemed to think the draw should be between 4.5 and 5 amps, and was somewhat troubled by this apparently high current use.
Any comments/suggestions? Thank you very much.

 

[Valveman]

The pressure tank is just so large that you are pumping the well dry while refilling the tank. The Pump Tec should be shutting the pump off when it sees low amperage from running dry. Then you can set the restart delay for say 10 minutes to let the well recover. With the large tank you will need to restrict the pump to the amount the well can produce to keep from pumping dry. If you restrict the pump to 10 GPM but the well only makes 9 GPM, you will still pump the well dry.

FLA or full load amps mean nothing as all submersibles pull SFA or Service Factor Amps. You would have been better off with a small tank, and I don't think your Pump Tec is working. We make device called the Cycle Sensor which also detects dry run and makes it is easy to see what amps the pump is pulling. If you don't get something that will shut the pump off on dry run you will need another pump very soon.

 

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[Frank Spurlock]

Thanks for the prompt reply. The gate valve was installed to diminish pump discharge. The initial dry run condition occurred before the gate valve installation when the pump was discharging ~ 16 or more GPM. I then installed the gate valve AND the Pumptec as a backup. The Pumptec appears to be working and detectin g dry run conidtions

The pressure tank is just so large that you are pumping the well dry while refilling the tank. The Pump Tec should be shutting the pump off when it sees low amperage from running dry. Then you can set the restart delay for say 10 minutes to let the well recover. With the large tank you will need to restrict the pump to the amount the well can produce to keep from pumping dry. If you restrict the pump to 10 GPM but the well only makes 9 GPM, you will still pump the well dry.

FLA or full load amps mean nothing as all submersibles pull SFA or Service Factor Amps. You would have been better off with a small tank, and I don't think your Pump Tec is working. We make device called the Cycle Sensor which also detects dry run and makes it is easy to see what amps the pump is pulling. If you don't get something that will shut the pump off on dry run you will need another pump very soon.

 

[Valveman]

Most of the time a Pumtec will see the lower amps created by restricting the pump with a valve, and will think the well is dry and shut off the pump. The Cycle Sensor was made to work with the low amps created by a CSV, so it knows the difference between a pump that is restricted to low flow and actually pumping the well dry. If you don't have to restrict the pump to less than 10 GPM, you might be able to make the pumptec work ok.

 

[Reach4]

It's good that things seem to be working for you.

I am not a pro, but I have a thought or two.

You might want to raise your pressure to 40-60 from 30-50 to get closer to the backpressure you are looking for.

Another thing you could consider is to switch to a digital pressure switch and set the pressure differential to 10 PSI, so the pump would run about half as long each time. The point would be to cause each run to not pump enough water to suck the water level in the casing down to the well intake. Examples are Amtrol GUARDIAN CP DC2 and Water Worker Model WWDPC . Maybe your mechanical switch could be adjusted to give a smaller diffential, but I have my doubts about that.

You would still want the pump protector.

 

[Craigpump]

Changing the differential is a piss poor way to try to control over pumping because you are essentially taking a properly functioning system and forcing it to short cycle, which we all know will lead to premature pump motor failure. In addition, that still doesn't address the issue of low yield or inadequate storage, the pump is still going to try to meet demand but the motor will destroy itself.

Apparently your water demands exceed your well yield, so you need to create more water for peak demands. Two options are to
1) install a static tank with a booster pump and controls
2) deepen your existing well or drill a new well.

 

[Reach4]

Changing the differential is a piss poor way to try to control over pumping because you are essentially taking a properly functioning system and forcing it to short cycle, which we all know will lead to premature pump motor failure.

Did you notice " my pressure tank 30 cut-in/50 cut-out drawdown volume of 27 gallons is refilled in about 2.5 minutes and everything seems okay so far."? Switching on the pump at 40 and off at 50 would still give about a 1.25 minute pump run time -- not that his current solution is a problem.

Too bad he does not have a 6 inch casing.

 

[LLigetfa]

The well is only 38 feet and 4" casing that is maybe slotted or maybe just open at the bottom. If it is slotted then maybe cleaning it either by chemicals or jetting, could increase the yield.

Maybe dropping it a foot or two might make a difference as well. I really doubt that the pumptec can actually detect the low level in time and it is likely to only detect after it sucks air. The Goulds does not drop the amps as much with a drop in water level as some other models do.

Also, in the first post a ball valve was mentioned and then later, a gate valve. I would never use a gate valve in that role as the gate is known to separate from the stem. Also, they are really sloppy so don't have the fine control that is needed.

 

[Texas Wellman]

The pump is pulling that many amps because it's pumping the maximum amount of water. In other words, the more water you pump the higher your amps will go up to the maximum pumping conditions. I do not have much experience with low flow wells, especially ones that are that shallow.

I will tell you something you can do and never have to deal with any of these problems again but it involves a different type of pump. Instead of rigging a submersible to manage the low well yield you can put a jet pump in with an in-well jet. Put a tail pipe below the jet about 34' long. Whatever the well makes the jet will balance. If the well makes 10 gpm the jet will only pull 10 gpm. If it makes 5 gpm it will make 5 gpm. I know that using a submersible is the best solution for most wells but this is one area where a jet pump will completely solve a problem like this.

 

[Craigpump]

It's really too bad he doesn't have an 8" well that makes 15 gpm, then he wouldn't have these issues!

But he doesn't, and setting the pump up to run on a 10 psi differential will dramatically shorten the motor life.

 

[LLigetfa]

IKWYM about a jet self regulating but with the static water level being 27 feet, there is only 7 feet to play with. Raising the pressure on a sub also moves it to the right of the curve but then again, one usually needs more than 7 feet of drop to play that.

 

[LLigetfa]

The pressure tank is just so large that you are pumping the well dry while refilling the tank...

A higher pressure would move the pump to the right on the curve and a CSV would slow the refilling of the tank and not cycle the pump to death.

 

[Frank Spurlock]

Thank you all for your comments. I guess I was unclear in the original post. The new pump overpumped only when initially installed. The discharge was probably approx 15-16 gpm I estimate from the pump discharge curve. Even though the well went "dry", it seemed to recover fairly quickly - within a couple minutes. However, I wanted to pump the entire pressure tank drawdown volume in one shot if possible, because I didn't want to rely on the pumptec to always shut off pump, and I didn't want to short cycle the pump (for example with a 10PSI differential) because it seemed there might be potential for shortened motor life. Ergo I then decided to both (1) use a BALL valve to increase pressure and reduce pump discharge, and (2) install the pumptec unit as a protective measure. At the 10GPM the well doesn't seem to overpump. After thinking about it, I am thinking of closing down ball valve a little more to maybe get about 7-8 GPM since well yield may decrease in the summer (although it's always been a good producer for 25+ years.

There is a misconception about how the Pumptec Pumpsaver works. The model I have monitors several things, including voltage in, volt/current equivalence between the 2 hot legs, and current drop that occurs as a result of impending drywell conditions. The Pumpsaver is first calibrated upon installation to determine "normal operating current". Then, the Pumptec sensitivity is adjusted to shut the well off if current drops below a user-specified current that is 70-90% of normal operating current. They recommend for low-producing wells to set closer to 90% as the pump shutdown threshold. I am using ~85%. I can only assume that is protective. In any event things seem to work now as the well doesn't seem to go dry. I would consider changing out the existing pressure tank only if other options didn't work. The well has always easily met our daily water needs.

I still don't understand valveman's comment that "all submersibles pull SFA or Service Factor Amps." According to Franklin Electric's discussion of SFA, the SFA is a threshold which shouldn't be exceeded to avoid eventual motor damage, but they imply that most pumps operate at currents somewhat lower than that. In any event, my original concern was whether the 5.9A with ball valve installed was "too high" considering that the SFA is 6.1A. I guess it's not, and further reducing pump discharge to 7-8 GPM will drop that somewhat anyway. Thanks again to all.

 

[Texas Wellman]

Instead of using a ball valve you might try instead a dole valve. A ball valve if accidentally closed could cause the pump to dead-head and overheat the motor.

 

[Texas Wellman]

Yeah it would not work the way I have used it in the past. I'm not sure if it would work the same way if used with a shallow well set-up.

IKWYM about a jet self regulating but with the static water level being 27 feet, there is only 7 feet to play with. Raising the pressure on a sub also moves it to the right of the curve but then again, one usually needs more than 7 feet of drop to play that.

 

[LLigetfa]

The pump draws more amps when it moves more water, so I don't understand why you are concerned about current draw when you slow down the GPM. The more you slow it down, the less amps it draws. Some pump brands drop amps faster than others due to how the impeller stages are floated.

I think everyone participating in this thread knows how a pumptec works. As water level in the well is drawn down, the pump moves to the right on the curve, slowing down the GPM and as a result drawing fewer amps. The way the pump saver is *supposed* to work is to shut off the pump before it draws down to the point of sucking air. Your well does not have enough variation (7 feet) between the static level (27 feet) and where is sucks air (34 feet) to have any confidence the pumptec will react before it sucks air. But hey, that's OK... some protection is better than no protection.

As for the ball valve (it is a ball valve I hope, not a gate valve), you could take a hacksaw to the handle to prevent accidental closure. On some you can remove the handle but sometimes the nut also holds the packing seal.

 

[Valveman]

Examples are Amtrol GUARDIAN CP DC2 and Water Worker Model WWDPC .

If you decide you want to try an electronic pressure switch you can get one here http://cpkits.com/collections/discontinued-product for 25 bucks. It works just as good as the Amtrol pressure switch. We still have hundreds of them available, but we discontinued making them because there is no way to make an electronic pressure switch dependable and long lasting like the old mechanical ones.