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Need new sub pump

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DogT

Active Member

Posts: 28

1

Thursday, May 1st 2014, 8:58pm

Need new sub pump

I have a 3/4 HP submersible pump that feeds the irrigation system (and the house) which has a max zone of 15 GPM. 250' deep well, pump at 200', not sure of the static and draw down levels. There is also a booster pump at the well head where the irrigation system taps off that was boosting the pressure to 80 psi or so (from the 40-60 from the pressure tank). The well I am confident can deliver well over 15 GPM, the driller told me it delivered 40 GPM when it was drilled and we have had no problems with water delivery, even running the hose full blast on a sprinkler all day long, day after day.

The issue is the booster pump electric wire has broken underground and I figure it's time for a new pump after 25 years and like the idea of constant pressure and I'd rather spend money on a new pump that a wire to the booster. The submersible pump will only deliver about 10 Gal/min initially and not sure what it is after the pressure tank drains, but I plan on measuring it. We actually only get about 5 G/min in the house from outside hydrants and less from inside faucets and of course flushing the toilet while taking a shower is not a good idea. The sub pump will not run the irrigation system without the booster pump much at all.

So, I'm looking at a new sub pump less the booster, maybe something like the Grundfos 15SQE15-290 system. Constant pressure system. Then I read stuff about the 'Stop Cycle Valve' and I get lots of conflicting information on the CPS (Variable speed pump) vs the SCV. I realize that to use the SCV I need to size my pump to the highest value I need, like 15 GPM or a bit more.

I get bad feelings about both the pump sellers and the SCV people, like they are just salesmen and I am concerned I'll be burned like I was with the irrigation system. That is I'll be spending more money than I need, the Grundfos dealer has quoted me $3800 for a full new installation 15SQE15-290 CPS. I haven't gotten any quotes from the Franklin or Gould people yet, and I have a new fellow that is going to get me a price for 'Tech' CPS? Never heard of that one. He was recommended by my well driller.

Is there anywhere to go to get good non-sales oriented information. I did call the local health dept. about the well and they couldn't recommend anything. I feel like I'm shooting in the dark here.

Dave

Wet_Boots

Supreme Member

Posts: 4,102

Location: Metro NYC

2

Friday, May 2nd 2014, 8:06am

You might first try an old-school solution. Assuming your tank has at least a 100 psi rating, you can bump up the pressure switch settings to let the pump operate continuously at 60+ psi output. Then you fiddle with the zones to match water consumption with supply. That's very simple with a PGP - just swap out nozzles with the next size smaller.


The idea here is to see whether it's possible to make a match with the existing water supply, and avoid the need for another pump beyond the existing one in the well.

The "40 gpm is available" is good news, but not a number you should bank on. Things change. That being said, if you did install a new pump that outstrips the well capacity, a new controller on the irrigation system could make up for that by adding some recovery time between zones operating.

If the existing pump alone isn't quite enough to make the zones work, then you might consider replacing the 3/4 HP pump with a 1 HP pump.

If the existing tank is a 75 psi rated unit, you might do well to replace it with a new one that has a 100 psi rating, as it gets difficult to set a standard pressure switch much higher than a 70 psi shutoff. There are replacement switches with higher pressure ranges, that can be installed in place of the original.

This post has been edited 1 times, last edit by "Wet_Boots" (May 2nd 2014, 8:29am)

DogT

Active Member

Posts: 28

3

Friday, May 2nd 2014, 9:33am

I doubt that will work for me. As I said, the pump alone will not supply the largest zone I have which is 15 GPM. As near as I can tell, the pump will only deliver 10 GPM, I think the booster helps it draw because we never have run out of water and it's only one zone that takes 15 GPM. The submersible alone barely gets the sprinklers out, the pressure drops to about 15 psi at that zone without the booster. I do like the idea of constant pressure in the house, and am willing to pay a bit for that, but mainly I need some pressure for the irrigation and I don't think the booster is worth messing with any more. It's outside in a little house that also covers the well head and is not the best place for it, plus now the ac line is broken and that will probably cost $500 to replace.

Other thing is trying to match the zones with the pump is that I have 21 zones and they vary from 5 GPM to 15 GPM. It would be very problematical to re-arrange the irrigation system. There is a combo of PGP and sprinklers, but I think any zone is one or the other, not mixed.

Wet_Boots

Supreme Member

Posts: 4,102

Location: Metro NYC

4

Friday, May 2nd 2014, 2:22pm

If the system can't be made to have consistent flow demands, by either changing nozzles, or by combining low-flow zones to run simultaneously, then the old-school approach is probably beyond you. I would be looking hard and long at how the existing system might be altered to run from a standard pump, before I plunged the thousands into the more exotic pump.

The Cycle-Stop-Valve is a technologically simple solution to mismatched zones. It makes a pump match a low flow demand by running it at a high-pressure-low-flow point on its performance curve, and reducing that high pressure before the water reaches the ground-level plumbing and controls. Without question, the CSV works. Its one theoretical misgiving is that it creates high pressures on the upstream side of the CSV, which makes for some possible worry about how an old polyethylene drop pipe in the well will react to higher pressures. With a brand new pump install, the drop pipe can be Sch 80 PVC or even galvanized steel, should you so desire, and drop-pipe worries disappear.

If the system is very flawed in its design, then you may need a high pressure at the supply connection, and the pump/CSV combination might become a 1-1/2 HP pump and a deluxe brass-body CSV, with an output pressure above the 60 psi available from the plastic-body versions.

What you should be doing in the here and now, is what should have been done a very long time ago, and that is to get the booster pump back in operation with an extension cord, and to take pressure readings at the pump output for each zone of the sprinkler system.

Without some hard numbers for what pressures are at the sprinkler system connection point, it's a bit difficult to state accurately just what will and won't make it work again.


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Another possibility for a replacement for the current arrangement is a 1 HP submersible pump, along with a lower-power booster for certain zones of the system. That combination might be operable from the same wiring that powers the existing pump.

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