New submersible pump - PVC vs Galvanized.

[Farmer_John]

I recently pulled a non-functional 5HP submersible from my irrigation well.
According to well records from the 60s when it was drilled, it is 80 ft deep with about 30 ft of steel casing.
(I pulled up 74 ft of pipe, so that fits with the records.)
The static water level is 8-10 ft down from the top of the casing, which is 2 ft above the ground.

Also according to the records, they were expecting 100 GPM from the well. This is consistent with more recent wells in the area that show 50 GPM @ 30 ft & 100 GPM @ 100 ft. (draw downs were 10 and 3 ft, respectively.)

Using the well for irrigation.
I understand that for a 5HP pump, ill need to use 2" pipe. im planning on going back down 70 ft plus the pump (20,20,20,10.) I also understand that start-up torque can be a concern.

Questions:
1) Am I correct that I'll need a 5HP pump to obtain 50 GPM @ 40/60 PSI
2) Am I limited to 2" galvanized pipe or will sch 80 PVC drop pipe work?
3) Can I even use a torque arrestor given that the casing doesn't go all the way to the bottom?
4) If I have to use galvanized pipe at the pump - can I switch to PVC 10 ft away from the pump assuming that there is less torque the further you are from the motor.

Thanks,
John

 

[VAWellDriller]

Your description of the water level and pumping level is a little unclear to me? You said well was 84, static was 8', but pumped 100 gpm at 100ft, and then said drawdown was 10ft and 3 ft..??

Anyway, you don't need 5HP to do the 50 gpm. (or really close)....a 3 or possibly even 2 HP will get it depending on the water level. You could use 2" PVC with either integral bell MXF, or threaded both ends with stainless couplings. I prefer the threaded both ends with stainless couplings. On an uncased well, I always use HD black jacketed pump cable...and I never use torque arrestors of centralizers ( I don't see many crooked or jagged holes). Look at pump curves for Goulds 45 and 65GS models. If you and clear up the water level data it would help make the right pick.

 

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[Farmer_John]

Your description of the water level and pumping level a little unclear to me?...

Thanks for the reply, sorry for the confusion. I'm not sure what my week is capable of and was comparing it to other wells in the area within 1/8 mile.

three wells:
mine - 80ft deep, 8-10ft static level with an expected flow of 100gpm (1960s documents)

comparison 1 - 30 ft deep, proven at 50gpm with a 10ft drawdown (1hr test)

comparison 2 - 100 ft deep, proven at 100gpm with a 3ft drawdown (1hr test)

so I'm speculating based on surrounding wells that I can get the 50gpm out of my well.

I looked at the curves fit the pumps mentioned, maybe I'm not reading them correctly.
the pump sits 70 ft down, with an additional 6ft rise (high point in the terrain)
I want 40-60 PSI, so that adds another 138ft of head. That plus the 76 ft gives a TDH of 214 ft.

Looking at the graph of the 65gs30, 200ft crosses at 32gp. Again, I may be totally out in left field with my calculations.

Thanks,
John

 

[VAWellDriller]

You are on the right track with TDH calcs....the variable we don't know is the drawdown....it doesn't matter where you set the pump, it only does the work of lifting from the water level. The system, and head conditions are very dynamic....I all cases the pump will start with water level at approx 10ft and 40PSI on system ...so approx 105' TDH....then as the water level drops and the pressure builds TDH will increase. The smallest combo I suggested 45GS20 will start puming 51 gpm....and drop down somewhere around 35-40. The 65 GS30 will start around 68 GPM and drop to around 35-40. Franklin makes a 60 GPM series pump that is a good fit for this application too.

At the higher flow range you will have to add a little pipe friction loss depending on what you choose. The PVC is available in SCH 120 or 80...both have published head loss charts. This is one of those applications where if it is all set up and sized right from the beginning you could set up to never cycle during use and skip any sort of variable drive or control valve. In all the worst case scenarios you may need a 5HP to get you the full 50gpm at 60 psi. If you go to a 5Hp I would probably switch to steel pipe to to torque.

 

[Farmer_John]

You are on the right track with TDH calcs...

Thanks!

I'll be dropping a 3hp pump in it next weekend. the good news is the pressure needed at the inlet of the system is only 20 psi - I wasn't factoring in the booster pump. So as long as the well will give up 50-60 GPM the 3hp shouldn't be an issue.

Question about the seal:
it's a split cast iron type - in planning on sandblasting and repainting it, getting new bolts etc.
What do I use for the rubber piece that is shot?
it looks like it should be replaceable, but Google has thus far been elusive on providing me any answers.

Thanks for all the info, I'm finally feeling confident about bringing this week back to life.

John

 

[VAWellDriller]

A new seal is the way to go....they are quite cheap relative to the rest of the project. It really doesn't matter in your case since you don't have much weight, but I prefer solid steel seals over split cast iron. If you really want to redo the one you have might look for a piece of old heavy conveyor belting. Sawmills and quarries usually have lots in their boneyards and it is useful for all sorts of things.