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Thread: Well for Sprinkler System

  1. #1
    DIY Member handyman923's Avatar
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    Default Well for Sprinkler System

    I am trying to design my sprinkler system to run off of my shallow well. My house is on domestic water. My sprinkler system will have spray heads and drip irrigation.

    The water level in the well is about 3' below grade and about 5' during pumping. I have a 1 hp Sears convertible jet pump with a 52 gallon precharged pressure tank. The pump has a 40/60 pressure switch. I get about 12 gpm at 45 psi output from the pump.

    I have read that I should be shooting for between 40-45 psi at the pump so I can deliver 30 psi to the sprinkler heads after losses. Does this sound about right? Do I design the sprinkler system to the full 12 gpm or some reduced value?

    How does the pumping system "know" to maintain the 45 psi I want it to? Since I have a 40/60 switch, the pressure in the system will start at 60 psi until the tank empties and go down to 40 psi when the pump first kicks on. Will the system automatically go to 45 psi if I have sprinkler heads that add up to 12 gpm? Do I need a cycle stop valve to keep the pressure constant?

    Also, do I need anything different for drip irrigation since the flow will be so low? Will it just use the water from the pressure tank?

    Thanks in advance for any help. I am new to wells, so I may be a little ignorant.

  2. #2
    Rancher
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    You either need a CSV before the pressure tank, or a pressure regulator after the pressure tank.

    Rancher

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you run a test and adjust the flow to 12 gallons/minute, what is your pressure? If the pump puts out what you want, just pipe it up and go. 30 pounds is fairly low for a sprinkler system. Figure out what pressure you really want, and adjust the flow with a valve until you get that pressure then measure the flow. Design the system with zones so you will use that flow rate at that pressure. As the pump ages, it may not have the same characteristics, though.

    The alternative is a CSV and/or or a pressure regulator...simpler is better, figureout what you can get, and design the sprinklers for that.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member handyman923's Avatar
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    Thanks for the replies!

    If I do decide to go with a cycle stop valve, say 50 psi, what do I set the cut-in/cut-out pressures at? 40/60? It seems to me that the pressure would start at 60 when a sprinkler zone starts, then fall to 40 as the tank empties, and then the pump would kick on at 40. Am I correct in that the pressure would then increase back up to 50 and then remain constant with the CSV? Or do I use different cut-in/out pressures?

    Thanks again!

    Dave

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If you are trying to get more water than the pump can supply, the pressure will drop. For a sprinkler system, you don't even need the pressure tank. You could just turn on the pump when you turn on the sprinklers. If you know the flow/pressure characteristics, design the zones appropriately. Basically, when running the sprinklers, run the pump full out.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    In the Trades Bob NH's Avatar
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    What kind of pump do you have? Submersible? Shallow well jet? Centrifugal?

    Get the flow/head curve. Plot a graph of pressure versus flow.

    Let's assume that you want to operate your system between 40 and 60 psi.

    What flow does the pump deliver at 60 psi? At 50 psi? At 40 Psi?

    Now draw a graph of your proposed irrigation system. You want to install an irrigation system that will use more water at 60 PSI than the pump will deliver at 60 psi, but will use less water at 40 psi than the pump will deliver at 40 psi.

    When the irrigation system comes on, the pump will start and the pressure will remain between 40 and 60 PSI as long as you are using the irrigation system.

    Since your pump is doing only irrigation, you can set the pressure switch to keep the pump running while irrigating.

    Your drip system is another story. I would not try to use a CSV; I would let it cycle on the tank. But if you want it to run constantly, make your drip system operate at the highest possible GPM. Then put in a second pressure switch and a selector relay so the power for the control valve for drip system selects the switch corresponding to that system.

    With a little care you can match the pump and the irrigation system. It may take another pressure switch and a relay to match to the drip system.

    If you have a shallow well jet pump, the characteristic is such that you should be able to run the pump into the irrigation system without a tank or pressure switch. You need to set up the system so it won't completely cut off the flow.

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    The CSV won't increase pressure. The pump can only do so many gallons per minute at any given pressure. More water flow less pressure and vise versa.

    If your pump does 12 gpm at 45 psi that's great. Just use large enough pipe to not cause friction loss and use the heads that add up to 12 gpm. Like the other guys said, the tank and switch is not necessary unless you want to do hand watering or wash the family dog/car. The switch and tank have absolutely nothing to do with how much pressure the pump produces.

    Where the CSV is handy is when your are using too little water to keep the pump running instead of cycling. Then you will want the CSV. This condition will only happen if your zones are not equal.

    bob...

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    DIY Member handyman923's Avatar
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    One more question... If I design one sprinkler zone for 45 psi and 12 gpm, but for some reason I end up with only 11 gpm of sprinkler heads, will system then operate at the 11 gpm with a pressure, let's say, of 47 psi? I guess my question is how much flexibilty do I have before my system begins cycling? Do I have to have the design exact or am I okay as long as I am operating somewhere between 40 and 60 psi (let's say 14 gpm and 8 gpm) for each zone?

    Thanks again!

    Dave

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    It's all up to your pump and where you set the pressure switch. Or install the 50lb CSV.

    bob...

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    In the Trades Bob NH's Avatar
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    With a pump that delivers 12 GPM at 45 psi, you will probably have somewhere in the range of 6 to 8 GPM at 60 psi. You will probably not get more than 15 GPM at 40 psi.

    I would hook it up without pressure switch or tank and let it pump. A jet pump will not overheat if you are pumping 3 or 4 gallons per minute and it has a limit on maximum pressure it can deliver.

    You just want to make the lowest flow circuit as large as possible, and keep the largest flow circuit low enough that you get adequate pressure. The pressure and flow tend to be self-correcting.

  11. #11
    DIY Junior Member Joe T's Avatar
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    What equipment do you need in order to switch the pump on when the sprinkler timer opens the zone valves? I am looking at a similar system as handymans but without the tank and switch and require automation due to water times needing to be greatly staggered.

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    My 1hp Betta Flo will produce 19 gpm at 50 psi. That is with the jet installed on the pump of course. You didn't mention if you had the jet for that convertable pump. If not, your maxed out already.

    If you don't use a switch and tank, you don't have to worry about anything, like BobNH said, if it's pumping a few gallons per minute, it will be fine. Or go with a Bronze impeller and don't worry. You won't find that one at Sears though.

    Joe T,

    You need a sprinkler timer with a motor circuit and a relay to operate the pump from the timers motor circuit. They are sold at irrigation supply stores or you can get one from me.

    bob...

  13. #13
    DIY Member jluksic's Avatar
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    mandatory sprinkler reading...

    http://www.irrigationtutorials.com/

  14. #14
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by Joe T
    What equipment do you need in order to switch the pump on when the sprinkler timer opens the zone valves? I am looking at a similar system as handymans but without the tank and switch and require automation due to water times needing to be greatly staggered.
    The valve system is probably 12 Volts AC, so the timer issues a signal to open each valve. If your timer system has an output that is turned on whenever any valve is open (a PUMP output), then you can use that signal to operate a relay that will start the pump.

    If your timer doesn't have a separate "Pump" output, then you need a small relay for each zone that will be connected to the coil of a contactor to start the pump.

    The coil of each relay will be connected to one of the timer outputs. The the common terminal of one of the poles of each relay will be connected together, and the corresponding normally open terminals will be connected together. Those terminals will be wired in series with the coil of the contactor so when any one of the relays is actuated it will close the contactor and start the pump.

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    No matter what system you go with, install a pressure relief valve. In case the solonoid doesn't operate and open the valve, the pump will still start and the pump will heat up. The prv will save the day.

    bob...

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