Question on sizing pump

[Sandy skinner]

Hi all,

I have a fairly unusual system and need a bit of advice. Our well is only 30 feet deep, and when the well was drilled in 1991' had a static water level of 8 feet. (the creek is fairly close by). At that time, when the pump was installed, the old house was located right there. The old house has since been torn down and replaced with a newer home about 400 feet away and at a 30 foot higher elevation. The well pump pumps uphill of the house another 200 feet and with another approx. 30 feet elevation gain to a 500 gallon storage tank buried in the side of the hill. Our water system in the house is entirely head pressure.

My question is I am not certain how to size a new submersible pump. Wouldn't we need to use the combined well depth and then the altitude difference of the tank where the water is pump to, in addition to the length of the pipe run? I have looked all over online and haven't found a similar situation to answers his question.

 

[Reach4]

I think you are saying that you plan to continue with about 13 PSI of water pressure to the house. If you get much more from your 30 ft head, your numbers are not right or I misunderstood. 13 PSI is very low, and most people would be needing/wanting more. It is more accurate to measure the height from the house to the tank by using a pressure gauge than with a tape measure or GPS.

So you want to climb about 68 to 80 ft from the well water surface to the tank water surface. I think you want a 1/2 HP pump nominal about 10GPM to 15 GPM submersible pump. Friction loss of 600 ft of 1 inch pipe at 10 GPM will be roughly 20 PSI. http://www.calctool.org/CALC/eng/civil/hazen-williams_p

So to account for the pipe friction, use the 20 PSI row. For the head, you will be working between 60 and 80 PSI columns I think. Some makers offer 12 GPM pumps, which would be a nice size.

With a 10 or 12 GPM pump, you could make a convertible system. With a valve, you could block off the uphill path to the tank. Add a pressure tank in the house along with a pressure switch, which would be used to control the pump. Electric goes out, feed the house by gravity. There is probably a way to accomplish this fairly eloquently without needing another pump.

 

[Sponsor]

 

[Valveman]

Yeah you need to add total elevation plus friction loss. A 10 gpm, 1/2 hp is probably good.

10 and 12 gpm pumps are usually the same. Some companies pick the 12 gpm spot on the curve so they can say their pump produces more than the other guy.

 

[Sandy skinner]

Thanks so much for the quick responses. I think I left out one pertinent factor. The well pump is not pumping. It's 25 years old, and it has been taking longer and longer to fill the storage tank. It normally takes an hour to fill when it's totally dry...but the last month or so I would run the pump for an hour and still not see any water come out the overflow. So I'm thinking that it has not been pumping properly for some time.

Tomorrow morning I am going to check the controller before we go any farther, though I don't suspect that is the problem. I had just wanted to get an idea of what the correct pump for this application would be.

Thank you for the charts, Reach4. These are helpful. Another factor that I didn't mention is that we are about 12 miles from the nearest power pole so we are completely off the grid. I like your idea of adding a pressure tank, but we have to keep our power consumption to a minimum.

One other question about pumps, guys. Is there info available anywhere which addresses the efficiency ratings of pumps? Would the 1/2 horse pump that takes longer to fill a tank be more efficient power wise that a 3/4 pump which could fill it in less time? Thanks again for your time on this

 

[Reach4]

One other question about pumps, guys. Is there info available anywhere which addresses the efficiency ratings of pumps? Would the 1/2 horse pump that takes longer to fill a tank be more efficient power wise that a 3/4 pump which could fill it in less time? Thanks again for your time on this

If we were talking KW, they would be about the same efficiency if you had bigger pipes to carry the higher GPM with a similar pressure drop and bigger wires to carry the current with a similar voltage drop. Unless you have a fixed size big generator that you will run mostly to fill the tank, I would think the 1/2 HP would be slightly better.

There are pumps that are more optimized for solar cells and can be driven from a wide range of voltages on both AC and DC. Those pumps cost more. https://us.grundfos.com/products/find-product/sqflex.html I think there is another brand that I forget the name of that has pumps aimed at solar.

Most pumps take extra current at start. So you would not need as big of a generator to start the smaller pump. There are pumps where this surge is less.

And while you are thinking about off-grid, search for "Simple Pump" to find a pump that can be installed simultaneously that is human powered for when the generator fails.

 

[Valveman]

A 1HP 20 gpm pump is no mre efficient than a 1/2HP 10 gpm pump. The 1HP will just fill the tank twice as fast but uses twice the current, twice as big a generator, and needs twice the size wire and pipe.

 

[Sandy skinner]

Thanks guys....1/2 horse it will be! And I did not know that there are pumps designed for solar applications. Makes sense though, I'm certain theres a need for it. We usually run our diesel generator when we fill the tank in the wintertime, but when the sun is higher we don't have to...except when I've got a bunch of power tools running. I think I will peruse that site and check those solar pumps out before we buy another pump. It might be fit our system better.

Thanks again guys. I feel much better about this now.

 

[Sandy skinner]

Forgot to mention, my well-driller son (he only drills...hasn't done pump yet...darn) is going to get mr a hand pump to install when we do the electric pump. I have always wanted one of those. I am a bit of a prepper....