Running a system off two different sized pumps

Discussion in 'Irrigation' started by Dirty Water, May 31, 2006.

  1. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    We are doing a install right now that has two water sources. One is a 1 horse pump that is pumping non potable water from a irrigation feed. This is only on 4 months of the year, and the client wants to be able to water from her well when this line is off.

    Her well pump is smaller than the irrigation pump, so there will be issues on running it off that supply if we designed it for the irrigation pump, but if we design it for the well pump it will cycle the irrigation pump.

    My first thought was to use a pump start relay on the irrigation pump, and use the pressure switch/pressure tank setup on the well pump, and design for the well pump.

    The problem is that we are putting in a yard hydrant, so using a PSR won't work.

    The idea I have right now is to wire a PSR directly to the 24v output on the timer, and wire a flowswitch in series with the PSR. My thought is that if water is moving, the PSR will activate the irrigation pump, but if there is no flow, the PSR stays off.

    We'll use a backflow and isolation valve to keep the flow switch and non potable supply seperated from the domestic well supply.

    Can anyone see a flaw with this idea?

    Also, do they make a flowswitch that activates when there is flow, instead of one that closes when there is flow?
  2. PurpHaze

    PurpHaze LawnSite Fanatic
    Messages: 5,496

    They must because we have one configuration of a booster pump that works off a flow switch. The main line splits right after the POC isolation valve. A 3" main goes to the sprinklers around buildings and in smaller areas and doesn't use the booster pump. A 4" main goes into the stadium field and the booster pump is activated by flow when these zones are on. There is a check valve so both systems can be on at the same time drawing from the same well pump.

    We have another system that also has a flow switch activated booster pump because wiring it to the controller would have been very difficult because of it's isolation across a creek.
  3. Valveman

    Valveman LawnSite Member
    Messages: 53

    It would be much more simple to use a Cycle Stop Valve on the 1 HP pump. Then this pump will not cycle even if you are only using 1/2 HP water.
  4. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    I've never used a cycle stop valve, but it sure seems like a "Band-aid" fix and not a good solution. Doesn't it just bleed off water (back to the source) to keep the pressure switch from flipping?
  5. Grassmechanic

    Grassmechanic LawnSite Silver Member
    Messages: 2,697

    That's the method that golf courses use when using multiple pumps.
  6. Valveman

    Valveman LawnSite Member
    Messages: 53

    The Cycle Stop Valve does not bleed off any water. It simply puts artificial head on the pump to vary the flow rate to match the usage. Not a "band-aid" either. The CSV is also used on lots of golf course systems and is an excellent solution to variable flow rates.
  7. SWD

    SWD LawnSite Senior Member
    Messages: 988

    Why not simply place downstream from the two pumps a pressure switch that would activate when the main line pressure drops below the set point?
    Couple this in with a Cycle Stop Valve per their instructions and it all should work together quite well.
    A quick note regarding CSV's. Use them, they work.
    I install them on all new systems, and have noticed much more uniform pressure flow through different sections with different gallonage requirements with these valves.
    Take a bit of time to research on the web and you'll see they work very well and are worth it.
  8. jerryrwm

    jerryrwm LawnSite Bronze Member
    Messages: 1,274

    Well the only problem I have is hooking the system up to potable and non-potable water supplies. Backflow devices - DCA's that you use up there, fail and the isolation valve is not a deterrent either. Too many variables that leave you open for liability problems or negligence.

    You might check the local codes and the state codes to see what they have to say.
  9. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    I understand your concern Jerry, but we have hundreds of houses out here cross connected with just a double check. Because of the large amount of irrigation ditches ran around this area, many people have it installed this way (not just us). Eventually codes will change, and I'll make a small fortune putting in RP's :)
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,758

    Just make sure the system has some pressure to spare, for when the change to RPZ devices happen.

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