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I am trying to design a system for irrigation of a garden area that has no access to grid electricity, but does have a 24V solar system. There is a spring/seep with a tank at relative elevation 0. There is a tank at the top of the garden at +70' elevation (500+ linear feet away from lower tank). The 24V solar system is at the bottom end of the garden, so in order to minimize the length/cost of cabling runs (and trenching) I was thinking of having a 24V DC water pump near there which is about 3/4 of the way between the lower spring/seep tank and the upper tank (+45' elevation from the lower tank, 350 linear feet). I am trying to assess the feasibility of having the tanks/plumbing/pumping configured such that I can use it in a number of different ways:

1) The simplest scenario is that I want to be able to run a gas or potentially 120VAC pump at the lower tank in order to pump all the way up to the upper tank (see bold black lines below):

2) The next priority is to be able to use gravity-feed irrigation from the top tank down to one or more yard hydrants:

3) At any yard hydrants near the top end of the garden (where the elevation differential is lowest) the pressure is going to be pretty horrible, so at best I'd just be opening a valve and letting water slowly run out. Farther down in the garden I might get 15-20 PSI, but probably not enough to be spraying using any sort of nozzle/sprinkler. So I'd like to have the option of using a 24V DC water pump in order to boost the pressure:

4) And then my final thought is that I could potentially even use the 24V DC water pump to handle pumping water all the way up from the lower tank to the upper tank. I don't want to get so large of a pump that it drains my batteries excessively, and I know that there are limits in terms of how far down an un-primed pump can pull from. So I'm thinking I might use a pump at the bottom to get things primed, and then maybe from there the 24V DC pump can take over.

Does all of this seem feasible? Any of this? :)

Once I've used the lower pump to fill all of the pipes up with water, and assuming I put some check valves in the right places (not pictured in diagrams) then in theory that water should "stay" in those pipes. Does that then obviate the need to re-"prime" things every time the DC pump goes to run? It would be really great if I could wire the 24V DC water pump to a float valve in the top tank (170' away) and have it kick-in to keep the top tank topped-off. But I'm still not sure whether my 360w/24V/135Ah solar system would be able to support a beefy enough pump to get water up 70+ vertical feet and 500+ linear feet. I've looked at a few that seem like they can do that with only a couple amps draw, but I'm looking for some confirmation on the overall feasibility of this.

Thanks!


Update:

After my original post I noticed that I had an extra/unnecessary valve/path between the 24V DC pump and the lawn hydrant, so I removed that one. I also moved things around a bit to reflect how all of the piping/valves might be laid-out within a below-grade valve box. I added in check valves in two places that would have unions on either side so that they could be reversed for winterization. Let me know if you have any comments/suggestions related to this updated diagram:

  • It sounds like it will work if you have 70' elevation you should have 31psi not great but it should work. If your pump can handle the head pressure I would add a float valve, in fact I would put at least 2 conductors if not 4 or 6 in the trench with the pipe so you could controll the pump. – Ed Beal Jan 25 '18 at 20:16
  • How would you power the 120VAC pump? Any wind in the area? – Harper - Reinstate Monica Jan 26 '18 at 9:32
  • Also you understand that our atmosphere is at about 15 psi pressure, and that means even an ideal pump cannot suction-lift water more than 30 feet, and realistically more like 15. – Harper - Reinstate Monica Jan 26 '18 at 9:46
  • There is 120V AC about 175' away from where the lower tank/pump would be, so I am still undecided on whether to bury conduit or use a gas-powered pump in that location. With check-valves in the correct places (review updated diagram) and the lines "primed" do you think the 24V pump would be able to handle all of the pumping: pulling water from below and pushing it up to the top tank? – Trevor Jan 26 '18 at 16:45
  • Update: My conclusion (based on discussions with the pump manufacturer) is that 45' of suction height is too much and that the pump needs to be situated at (or at least reasonably close to) the lower tank in order to minimize the suction height. So the concept of having a pump in the "middle" of the system that could be used both for "sucking" water from a low tank and also "pushing" / pressurizing water from an upper tank is out the window. :) – Trevor Feb 20 '18 at 21:59

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