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I have a 40 foot deep 6 inch drilled well. Currently it has an old 3/4 horsepower jet pump, but it is shedding bits of rusty metal into the return pipe which are getting clogged in the foot valve. Everyone is recommending that if I have to replace the pump, I switch to a submersible, but nobody can say why other than "they are better". What are the actual benefits of a submersible over a jet pump (other than being capable of greater depth which doesn't matter here)? Do I need to get a 3/4 HP submersible, or would a 1/2 be fine since they say they do 12+ GPM at 40 feet?

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Jet pumps were a great idea when pump motors were terribly unreliable, and you could keep the pump motor out of the well by using one.

These days, that's not true. Likewise, anyone who recommends a "3-wire" submersible is also living in the past. Things have changed. I'd suggest a 2-wire pump (there are 3, but one is the ground, and not counted as per usual - "3-wire" pumps use 4 wires for the same reason.) 3-phase is a different deal and un-applicable to most folks with individual water wells. Personally, I prefer a stainless steel pump.

Advantages of a submersible pump other than greater depth capacity -

  • much more power efficient - you pump the water once, that is it. You don't pump a lot of water around in circles to pump less water out of the well, which is roughly what a jet pump does.
  • You don't need to prime it. So much simpler. Drop it in the well and apply power, out comes water.

If they made them, you could probably use a 1/4 HP pump on that well. Last time I was shopping pumps, 1/2 HP was the smallest they made. You may need a restrictor valve (or orifice/plate) to keep it happy.

In the same counterintuitive manner that fans draw LESS power when restricted, non-displacement pumps also draw less power when restricted, and can draw too much power if unrestricted with low head. The short and simple explanation is that it's doing more work (moving more water) when un-restricted, and doing less work (moving less water) when restricted. Most people not already aware of this won't believe it until it is demonstrated with an ammeter and a valve.

Likewise, if your well can't keep up with 12 GPM you'd want to restrict the pump for that reason.

  • So I would want a restrictor because a 12 GPM pump is way more than the drawdown of my tank, correct? Right now I've got a puny 15 gallon tank, which says its a 1..8 gallon drawdown. So the pump would be cycling on for just a few seconds. Should I get a bigger tank too? – Bob Aug 22 '16 at 22:10
  • Either a larger tank (my default choice) or a "constant pressure valve" (so called) which is essentially a leaky pressure regulator and claims to let you get away with a very small pressure tank. I've read about them and the idea seems plausible, but I haven't personally bit. A variable speed constant pressure pump is another option, but on the expensive side of the options. – Ecnerwal Aug 22 '16 at 22:25
  • Flotec says I should have the drawdown be equal or higher than the capacity of my pump. But the biggest tank I can find is still only a 5.8 gallon drawdown, and the smallest submersible pump has a 10 gallon capacity at 40 feet. Should I just be sticking with a jet pump? – Bob Aug 22 '16 at 23:01
  • If the biggest you can find is 5.8 gallons you are either shopping at the wrong place or operating at extreme pressures. My tank has a 7 gallon drawdown at 50/30 off/on - and it's a long ways from the largest tank made - but it's easy to find a bladder tank with 36+ gallons of drawdown from 50/30 (it's a 119 gallon tank, and not cheap, but you don't need it that big anyway, just an example.) If you restrict the pump properly (adding dynamic head) you will ALSO reduce the actual maximum flow rate that it produces from your well, which works back to not needing as large a pressure tank anyway. – Ecnerwal Aug 22 '16 at 23:38
  • Ok, I found a store a few towns over that has a bigger tank, but it still isn't quite 12. Would I need a restrictor with this combination of pump and tank? flotecpump.com/ResidentialProduct_fl_hw_tk_FP7120.aspx redlionproducts.com/clean-water/4-submersible-well-pumps (the top one: RL12G05-2W1V) – Bob Aug 23 '16 at 0:32

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