Well pump sizing check:

[rural_engineer]

Hi,

I was hoping that I could get someone to double check that I'm picking my pump correctly. I'm building a house on a farm that has an existing well that was drilled in 1987 but was never used. It's 28' to the bottom, and 12' to the end of the casing. I'm not entirely sure where the water line is, but it was high enough for a submersible pump held a foot or two off the bottom. The original markings in the well cap indicate that it can support 50GPM. I had a guy out with a portable pump a few days ago, and he confirmed that it supports 12GPM without dropping the water level at all. After the initial gunk from sitting 30 years, the water ran completely clear.

I want to confirm that I am sizing my pump correctly. Here's what I know:
Well depth: 28'
Rise to house: 10'
Distance to house: 355'
Desired flow: 25GPM ( For farm work, filling water tanks, filling a hot tub, etc.)
Desired Cutoff Pressure: 60PSI (138' of head)

1.5" DR 11 PE4710 pipe supply line: 22' of head (for 400')

PK1A Pside-kick (20PSI friction loss or 46' of head)

Total head: 244'

Looking at the curves, I think I'm looking at a 2hp motor.
Grundfos 25S20-11: 220' of head at 25GPM
Goulds 18GS20: 220' of head at 25GPM

Did I do this right, or am I way off base?

--John

 

[Valveman]

You are right on target! I would opt for the 25S20-11 for three reasons. The Grundfos will drop more in amps when using small flow rates than the Goulds. The 25S will only have 136 PSI back pressure from the CSV, where the 18GS will have about 190 PSI back pressure. Plus the 25S will have fewer impellers and should cost less. But either of those pumps will work fine.

You will really like that system. You could also go up to the 10 gallon tank on the PK1A because you will have a 2HP, which is max we recommend with the 4.5 gallon tank. Plus the 10 gallon tank is also suggested when up-ing the pressure switch to 50/70, which you will have plenty of pump to do, and you may like the extra pressure.

 

[Sponsor]

 

[VAWellDriller]

You are right on target! I would opt for the 25S20-11 for three reasons. The Grundfos will drop more in amps when using small flow rates than the Goulds. The 25S will only have 136 PSI back pressure from the CSV, where the 18GS will have about 190 PSI back pressure. Plus the 25S will have fewer impellers and should cost less. But either of those pumps will work fine.

You will really like that system. You could also go up to the 10 gallon tank on the PK1A because you will have a 2HP, which is max we recommend with the 4.5 gallon tank. Plus the 10 gallon tank is also suggested when up-ing the pressure switch to 50/70, which you will have plenty of pump to do, and you may like the extra pressure.

Don't you think a different CSV would serve him better? Awful lot of headloss at 25 gpm through that valve, be almost impossible to set a pressure switch to work right at both low volume domestic use and also at the higher flow rates. He could go down to 1HP and still get close to 24-25 gpm and save a lot on equipment with a less restrictive csv.

 

[rural_engineer]

Would I be better off with a CSV125-1 in the well? Would I also want to switch to 2" pipe from the well? That reduces the head to 182'. I could then switch to 25S15-9. It looks like I might save $180 total with these changes.

My concern is that I don't know if I'm going to get any sand and grit from the well in the long term.

--John

 

[Valveman]

Don't you think a different CSV would serve him better? Awful lot of headloss at 25 gpm through that valve, be almost impossible to set a pressure switch to work right at both low volume domestic use and also at the higher flow rates. He could go down to 1HP and still get close to 24-25 gpm and save a lot on equipment with a less restrictive csv.

Yes sir you are correct. Just like 2HP and 50/70 is the recommended max for the CSV1A and PK1A, 25 GPM is also right at the max. These are the points where it pays to look at the next larger CSV. The CSV12560-1 would work great for this application. It would only have 2 PSI friction loss at 25 GPM, where the CSV1A has 20 PSI loss. This change by itself would not be enough to use a smaller pump, the 2HP would still be needed. However, changing to the CSV125 AND changing the 1.5" pipe to 2" WOULD allow for a 1.5 HP pump to do the amount required.

I would recommend installing the CSV12560-1 in the well just under the pitless adapter. This would be a good thing as you can tee into the main line anywhere you want, and still have the little pressure tank and switch in the house. The main reason for installing the CSV125 in the well, is because if you do have sand or sediment, it will cause the CSV125 to leak a few drops. If it is in the well that little drip of water won't hurt a thing. But it would make a wet spot on the floor if it is installed indoors.

The different way the spring chamber in the CSV125 vents to atmosphere is what causes it to leak if you pump sand. But it is also the reason why it has so little friction loss and holds such good constant pressure.

If you want an adjustable CSV that does not leak when installed indoors, the CSV1A you first chose is a good choice. You could also step up to the larger CSV2W/1 GPM, as it will have less friction and pressure loss than the CSV1A. But with either of these valves you will still have enough friction loss that the 2HP pump is needed. And for 180 bucks difference, I think I would stay with the 2HP no matter which size pipe and CSV is used. One of the benefits of a CSV is that it allows you to install as large a pump as you want, and still let you use it like a really small pump without hurting a thing. Sand and normal wear can reduce the pumping capacity of the pump, and the 1.5HP could wear down until it is not producing the flow required. The 2HP would be able to wear a lot more and still produce the 25 GPM you need.

 

[rural_engineer]

Thanks! So long as a little bit of grit isn't going to destroy the CSV125, it seems strictly better.

--John

 

[rural_engineer]

A quick update: I now have a strong case for the 1.5HP pump. I can use a two wire motor, thinner wire, and no control box, saving a lot more money.

--John