New well - pipe size and pressures

[JProspect]

I am in the process of designing a new well setup for our future home and hoped that I could get a sanity check on some of my numbers. I have lurked here for a while and appreciate the expertise and regional perspectives on this forum!

Well:
Approx 10 gpm (possibly a bit less in dry season)
6" steel casing to 18', bedrock to 250'
Static level 20'
Dynamic level 170'
Pessimistic dry year guess 200'

House:
130' elevation above well head
900' horizontal distance
Very rocky soil

I am looking at using 1-1/4" PVC sch40 or HDPE poly for the in-ground pipe and installing a 1.5HP 7gpm pump. The various calculators tell me that 1200' of pipe would add another ~15' head (plus some for fittings) and the water would travel at 1.8 fps in the pipe.

Adding in the 60psi for the house at high pressure, that would add roughly 140' head for a total of about 485 ft head. That converts to roughly 210 psi at the pump in a dry year:

200' well
130' elevation
15' friction
140' house @ 60psi
---
485' total head

Question 1: If I go to 1" pipe, the friction jumps from 15' to 43' of head. I haven't really added anything for fittings at this point. Does my choice of 1-1/4" seem about right?

Question 2: I would like to use HDPE black poly pipe in the well, since it would be easier to pull by hand. I had a reasonably positive experience pulling a previous poly well and think threading PVC sounds like a chore. However, it seems hard to find HDPE to handle 210 psi + safety margin. Should I just use Sch80 PVC in the well instead? Can anyone comment on handling thick-wall black poly?

Question 3: For the in-ground part, I don't mind gluing PVC but, with rocky soil, I am not sure if I should also use poly for that. Since the pressure is less from the well head upward, I think I can use 160psi or 200psi poly. We are in a seismic region and wasn't sure if poly might also handle shifting better than glued PVC? However, straightening hundreds of feet of stiff poly may be just as much work as gluing PVC.

Question 4: I like the idea of a CSV, but I am worried about increasing the back-pressure at the low end of the pipe. I think the pump could take it, but I don't know about putting even more pressure on poly drop-pipe. We are mostly a household of 2 (occasionally 4) and it looks like the CSV shines more in higher-demand situations. Thoughts?

Thanks again for any feedback. I have found a lot of the older threads here very educational.

 

[JProspect]

I should add that I have been looking at various pump curves and it looks like there are a few possibilities of motor between 1HP and 1.5HP combined with a pump doing 7gpm to 10pgm. I am using (very rough) numbers of 300 ft to 500 ft total dynamic head and it is interesting to compare the different pump curves out there.

 

[Sponsor]

 

[Valveman]

Yeah it is only a 7 GPM pump. So, without any irrigation just use a 44 gallon tank that holds 10 gallons of water and let it cycle. The back pressure on the pipe when using a CSV would be 294 PSI, which is too much for the CSV and even for 250# pipe. Even without the CSV there will be 209 PSI on the pipe. You will still either need 250# poly or sch 120 PVC. You don't thread the PVC, it comes that way.

You may not need the high pressure rated pipe in the ditch, but the heavy wall pipe is also better in rocky ground. 250# pipe will be really stiff and hard to work with, but it still probably your best choice.

 

[Reach4]

I would choose 3/4 HP for that 7 gpm pump. Maybe set the pump at 200 with a flow inducer sleeve.

The water is unlikely to fall that deep, but the water flow would reduce as you approached that level.

 

[Valveman]

Since your "dynamic" level is 170'-200' a 7 GPM 3/4 HP would work. Then the back pressure on the pipe and CSV would only be 177 PSI.

 

[JProspect]

Thank-you both for your thoughts. Although my dynamic level in the well is only 170', I also have 130' of elevation and 15'+ friction loss. Without including the house pressure, that is 315' of head. Reach4, unless I am reading your table wrong, that would make the 1HP pump the smallest I could get away with. Is that a Franklin pump table?

Any thoughts on going with 1" vs 1.25" pipe for the whole thing?

 

[Reach4]

Your analysis is quite astute. I missed that. The pressure tank and switch are at the well house or the house? Note that the Well-X-Trol pressure tanks are rated for higher pressures than many are.

Anyway, yes, I missed that aspect.

Thank-you both for your thoughts. Although my dynamic level in the well is only 170', I also have 130' of elevation and 15'+ friction loss. Without including the house pressure, that is 315' of head. Reach4, unless I am reading your table wrong, that would make the 1HP pump the smallest I could get away with. Is that a Franklin pump table?

I think it is a Franklin V pump table. You should be able to find similar tables for other pumps. The values are usually fairly close between pumps. I like the fact that that table has the shaded and non-shaded areas.

Any thoughts on going with 1" vs 1.25" pipe for the whole thing?

Not sure. You could use 1 inch down the well, and switch to bigger for the path up the hill. That way you are hauling less weight up and down. Your pipe above the well house will not see as much pressure.

http://www.pressure-drop.com/Online-Calculator/ has a "Group" drop-down list for figuring elbows and transitions. The pressure drops add.

When you run pipe above ground, you want to take into account the temperature changes. https://terrylove.com/forums/index.php?threads/tips-for-400-ft-pipe-run.74073/ has a link with considerations for poly. http://www.charlottepipe.com/Documents/PL_Tech_Man/ExpansionandContraction.pdf has info for poly and PVC too.

 

[JProspect]

Thanks again. In revisiting my numbers, I think I can keep the pressure at the pump pretty close to a max of 200psi (except for rare events), which would make sourcing the HDPE pipe a lot easier.

The pressure tank and switch are at the well house or the house? Note that the Well-X-Trol pressure tanks are rated for higher pressures than many are.

Although Vancouver Island is warmer than most of Canada, the standard is still to do a pitless adapter and have the switch/pressure tank in the house. So, the switch should only "see" the house pressure.

You could use 1 inch down the well, and switch to bigger for the path up the hill. That way you are hauling less weight up and down. Your pipe above the well house will not see as much pressure.

Interesting. I hadn't thought of that. Thanks for the idea.

When you run pipe above ground, you want to take into account the temperature changes. https://terrylove.com/forums/index.php?threads/tips-for-400-ft-pipe-run.74073/ has a link with considerations for poly. http://www.charlottepipe.com/Documents/PL_Tech_Man/ExpansionandContraction.pdf has info for poly and PVC too.

Good point. Your comment in the other thread about "snaking" the pipe was interesting.