Submersible Well Pump Sizing Help Please

[Regis Tration]

I have a well in an extremely remote location on an island 10 miles off the coast of Maine. I would hire a professional to help but I haven’t found anyone who is willing to travel out there on a boat.

The submersible well pump needs to be replaced. I need to know what size pump to buy. I don’t know the size of the old pump. I power the pump with a small generator. I can’t travel to the well to pull the old pump in advance of buying a replacement pump.

The water is pumped into a pressure tank. I don’t care about the flow rate because I use the water from the tank only when the pump is off, and I only run the pump after the tank is empty.

The old pump is 230/240 volts, 3 wire. When it was running, after the initial startup surge, each of the two legs of the circuit would draw about 5.4 amps at 112 volts. Is that enough information to determine the horsepower of the pump, or a specific recommended pump?

If the horsepower can’t be determined by the electrical characteristics, my best guesses for the operating environment are:

• the well is believed to be at least 300 feet deep, 300-320 feet
• pump is believed to be at 300 feet
• flow is believed to be 1.5 gallons per minute (?)
• pump switch shut off pressure = 50 psi
• vertical lift = 60 feet
• static water level = 30 feet (?)
• pumping level = 75 feet (?)
• horizontal distance from the well to the water tank = 277 feet
• plastic water pipe = 1 inch inside diameter
• friction loss = 14 feet (?)
• the well casing is steel 6 inches in diameter
• the wires running down into the well are 12 gauge

Could you recommend a pump horsepower, or a specific pump, based on those characteristics?

I have only a small generator, so I need a pump that consumes as little power as possible.

What would be the consequences of using a lower powered pump that doesn’t quite meet specifications? Would the water never reach the tank, or would it just reach the tank more slowly?

I was hoping that I could use a 1/2 horsepower pump. Any specific recommendations for a high efficiency pump would be appreciated.

Thank you in advance.

 

[Reach4]

You have fairly high static level. Do you want a pump that can pump from 300 ft if the water level falls that far, or shall we presume that the water will only fall to 100 to 150 ft? A 6 inch casing stores about 1.5 gallons of water per foot.

How many PSI do you want to pump into your tank?

We are pretty much thinking of a 1/2 hp 3-wire pump or a Grundfos SQ pump.

Do you want the option of running one of those small quiet 120 volt only generators, such as the Honda EU2200i?

 

[Sponsor]

 

[Valveman]

5 amps means 1/2 HP. If the pumping level is really 75' I would set a 10 GPM, 1/2 HP at about 100'. But the 1.5 GPM flow rate and a pump settign of 300' makes me question the 75' pumping level. In that case I would probably show up with a 5 GPM, 1/2HP pump and be prepared to set it back at 300'. You would need at least #8 wire to use 115V at 300', so stay with 230V. A 5 GPM, 1/2HP, SQ type pump would weigh a few pounds less and be smaller in diameter, but will cost more than a regular 4" pump, which you can get in many brands.

 

[Regis Tration]

You have fairly high static level. Do you want a pump that can pump from 300 ft if the water level falls that far, or shall we presume that the water will only fall to 100 to 150 ft?

How many PSI do you want to pump into your tank?

We are pretty much thinking of a 1/2 hp 3-wire pump or a Grundfos SQ pump.

Do you want the option of running one of those small quiet 120 volt only generators?

I use very little water. The pressure tank is an old Amtrol WX-302 Well-X-Trol, which is rated 86 gallons. Based on my low water usage, I don't think that I would need to pump from 300 feet to fill the tank, but I would prefer to put the replacement pump at the same 300 foot depth as the old pump if possible.

The pressure switch is 30-50 PSI so I assume that the tank pressure should be somewhere in that range.

That's a really interesting question about the generator. I can stay with 240 volts. I wish I could run 120 volts, but the wiring at the house and pressure tank, which are 277 feet away from the generator, is for 240 volts and I think it would be difficult to convert to 120 because of the amperage increase for 120 volts. (Maybe the two 120 legs could be bonded together to gain amperage capacity? - Anyway, probably can't solve that right now.)

Thank you, very interested in your recommendations and comments.

 

[Regis Tration]

5 amps means 1/2 HP. If the pumping level is really 75' I would set a 10 GPM, 1/2 HP at about 100'. But the 1.5 GPM flow rate and a pump settign of 300' makes me question the 75' pumping level. In that case I would probably show up with a 5 GPM, 1/2HP pump and be prepared to set it back at 300'. You would need at least #8 wire to use 115V at 300', so stay with 230V. A 5 GPM, 1/2HP, SQ type pump would weigh a few pounds less and be smaller in diameter, but will cost more than a regular 4" pump, which you can get in many brands.

The 75 foot pumping level was just a best guess and I am getting the impression that it wasn't such a good guess!

Thank you.

 

[Reach4]

Grundfos 5SQ07-270-230V looks like a good choice to me. Your generator should be able to start and run that through 14 AWG wire no problem. 3/4HP, but this design is very easy on generators.

The 5SQ05-180 in either 115v or 230 volt would be sufficient if your water stayed pretty high.

 

[Regis Tration]

Grundfos 5SQ07-270-230V looks like a good choice to me. Your generator should be able to start and run that through 14 AWG wire no problem. 3/4HP, but this design is very easy on generators.

The 5SQ05-180 in either 115v or 230 volt would be sufficient if your water stayed pretty high.

Thank you. Could I get away with a 1/2 horsepower, and if so, could you recommend a specific model?

 

[Reach4]

Others will know better, but if picking, I would look at Goulds 5GS05412C with 3-wire control box included.

Such a pump might be harder on the generator than the 3/4 HP SQ, but I think your generator is up to it.

You could try dropping an icecube down the well, and listen for the plop. Recording with your cellphone could make timing more practical. I have not done it.

 

[Regis Tration]

Others will know better, but if picking, I would look at Goulds 5GS05412C with 3-wire control box included.

Such a pump might be harder on the generator than the 3/4 HP SQ, but I think your generator is up to it.

You could try dropping an icecube down the well, and listen for the plop. Recording with your cellphone could make timing more practical. I have not done it.

Sorry everyone I made a mistake, the current pump is 2 wire. Not sure if that makes a difference in your answers. There is no control box, the wire runs straight to the pressure switch.

 

[Reach4]

Franklin AIM manual suggests generator KW and KVA ratings for generators powering different sized pumps. This note should be of interest:

Table 5 Engine Driven Generators
NOTE: This chart applies to 3-wire or 3-phase motors. For best starting of 2-wire
motors, the minimum generator rating is 50% higher than shown.
​

That would certainly not apply to the SQ pumps, which are all 2-wire.

​

 

[Valveman]

I see why Reach recommended the 5SQ07-270-230V. The 5SQ05 just won't quite go that deep. I also agree, especially with 2 wire, that the 3/4HP in the SQ would be easier to start from a generator than a 5GS05. Technically Grundfos makes 3 different models of the 3/4HP in the SQ, and the 270 is not a full 3/4 HP load like the 320. But your generator won't have any problems with the standard 5GS05 and it would probably be much less expensive.