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Thread: Pressure Switch with auto low pressure cut off

  1. #1
    DIY Member techinstructor's Avatar
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    Default Pressure Switch with auto low pressure cut off

    I am considering purchasing a Square D FSG2J24M4CP Water Pump Pressure Switch with Low-Pressure Cutoff for the pressure tank connected to my well pump. We have a very deep well (420') with a high static water level 40' but low recovery (2 gpm). We like high water pressure so we wanted a switch that was set at 40/60 (though I'm aware that these can be adjusted). I was advised to get one with a manual low pressure cut off that would turn off the pump in the event the pressure dropped too low from using the water up faster than the well could recover it. I found a pressure switch that had the manual low pressure cut-off lever on the side of it, but it was preset at 20/40. In looking for a 40/60 version, the one shown above is the only one I've found. It is preset at 40/60 and is supposed to cut off automatically if the pressure drops below 40. Is it safe to assume that the pump would be turned back on automatically when the pressure reached 40 again? Any suggestions as to how this switch will work in my given situation would be appreciated.

    Thanks in advance.

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by techinstructor View Post
    We have a very deep well (420') with a high static water level 40' but low recovery (2 gpm).
    How many hp is your pump? Thanks.

  3. #3
    DIY Member techinstructor's Avatar
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    Quote Originally Posted by Thatguy View Post
    How many hp is your pump? Thanks.
    It's a Myers Predator 1 HP. It was selected by the guy we hired to have the well drilled and he installed the pump. (I was later told by others that a 1/2 HP was actually the proper size for a 2 gpm well, but it's in there so we'll make it work.)

    Quote Originally Posted by another voice
    You have to manually hold down the lever until the pressure goes above low set point..
    The only picture I can find of the product I'm considering does not show a lever, hence my concern. The plumbing store does not carry this product so I have to order it online.

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    Homeowner Thatguy's Avatar
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    Yeah, I get 0.54 hp.

    Head= 420 feet
    Req'd pressure is 50 PSI
    then, equivalent head = head
    + (pressure x 2.307)
    Equivalent Head= 535 feet
    Req'd flow rate = 2 GPM
    Then,
    Req'd Power @ 100% eff. 0.27 hp
    Power @ 50% efficiency= 0.54 hp
    Power @ 20% efficiency= 1.35 hp

    So with 1 hp you can get 4 GPM.

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    DIY Member techinstructor's Avatar
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    Thanks for the responses and the specs on the water flow from the pump. I'll check by with the plumbing place. I suspected the sales rep didn't know what he was talking about when he said it wasn't available. Next time I'll talk the another salesman who seems to be the one at the company who is most competent and has been very helpful in the past.

    Thanks again.

    TI

  6. #6
    General Engineering Contractor ballvalve's Avatar
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    I have several GRAINGERS low pressure cut out switches, probably made by square D. 50- 70 preset, 40-60, and Perhaps some other presets. Even your 20 - 40 can usually be tweaked to do almost 40 to 60.

    I have a few 2 gpm wells, and while the low pressure cut out is essential, its a pain to be always re-setting it. It will not restart the pump.

    You should have a Franklin pumpsaver-pumptec, which has a adjustable reset time when it senses low water. I'll look for some links and edit them in here...

    I don't know this store, but use it as a start point.

    http://store.thepumpwarehouse.com/pr...hes/Categories

    .http://store.thepumpwarehouse.com/pr...Pumptec/Detail

    Heres the Graingers link - everything in the world here:
    http://www.grainger.com/Grainger/pre.../N-8gnZ1z11l12

    Note that if you have a Franklin 3 wire pump control box with a QD [quick disconnect] box, you can buy the $115 pumptek and plug it directly into the box. Incredible insurance policy for the cost.

    If you have any large needs, however, start budgeting for a 2 or 3,000 gallon storage tank.
    Last edited by ballvalve; 11-21-2010 at 04:10 PM.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    If the pressure drops below 40 psi and the pump shuts OFF, (meaning there is no further water flow), HOW is the pressure going to rise above 40 psi to turn the switch on? There is no way for that to happen, which is why it has to be reset manually.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by hj View Post
    If the pressure drops below 40 psi and the pump shuts OFF, (meaning there is no further water flow), HOW is the pressure going to rise above 40 psi to turn the switch on? There is no way for that to happen, which is why it has to be reset manually.
    Maybe somebody makes an auto reset that waits for some interval of time or uses some other method to decide when to try again.

  9. #9
    General Engineering Contractor ballvalve's Avatar
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    See my pumptek link above.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Maybe, but not likely, since it would be up to the homeowner to decide when the well might have recovered enough to start pumping water again.

  11. #11
    General Engineering Contractor ballvalve's Avatar
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    pumptek has a adjustable reset time, and if still in a no water condition, starts the timing over again.

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