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Thread: Pressure switch replacement

  1. #1
    DIY Junior Member mrron's Avatar
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    Default Pressure switch replacement

    I had a well installed early this year with a tank and pressure switch. I use the system to water my lawn. After 5 months of use the Merrill MPS4060 switch failed. Seems like the contacts broke and shorted. The inside of the plastic cover and inside melted. I obviously thought I should get more than 5 months out of it. In searching for a replacement I found, based on reviews, that this is a common problem. Luckily, the pump seems OK. Does anyone have a suggestion for a replacement that is durable. I assume they are plastic since some people would locate it outside or are they cheaply made. thanks. Ron

  2. #2
    DIY Senior Member craigpump's Avatar
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    Pressure switches aren't what they used to be, but it should have lasted longer than a few months. Are you sure the pump isn't short cycling against a water logged tank and overworking the switch?

  3. #3
    DIY Junior Member mrron's Avatar
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    If you mean that it comes on and off at pressures other than 40/60 all I can say I have watched the system operate (when it was operating) and it came on and went off when it was supposed to. The tank also is only 6 months old and by water logged you mean the bladder is punctured not sure but I can hear it expand and contract. When I install a new one I can do any test you suggest. Thanks for responding.

  4. #4
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by mrron View Post
    I had a well installed early this year with a tank and pressure switch. I use the system to water my lawn. After 5 months of use the Merrill MPS4060 switch failed. Seems like the contacts broke and shorted. The inside of the plastic cover and inside melted. I obviously thought I should get more than 5 months out of it. In searching for a replacement I found, based on reviews, that this is a common problem. Luckily, the pump seems OK. Does anyone have a suggestion for a replacement that is durable. I assume they are plastic since some people would locate it outside or are they cheaply made. thanks. Ron


    That is a very cheap switch, $10.00

    I would put in a better switch, May cost you $20.00

    http://www.amazon.com/Square-Schneid.../dp/B000BQSERE

    What is the HP of your Pump Motor ?


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  5. #5
    Moderator valveman's Avatar
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    If your pump is less than 2HP, as DonL is asking about, and the tank is not waterlogged as Craig is asking, then a burned pressure switch is one of the first signs of too much cycling on and off. “Coming on and off when it is supposed too” can still be too much cycling and burn up a pressure switch, starter, motor, or all of the above.

    When you are running sprinklers or anything for more than a few minutes at a time, the pump should run continuously and NOT BE CYCLING ON AND OFF AT ALL.

    Even the Square D switch now has a plastic contact holder instead of the old fiberboard. Any long term cycling will melt the switch, which is just an indicator of more problems to come.

  6. #6
    Jack of all trades DonL's Avatar
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    The problem with a lot of the cheap switches is that the contact plating is no good. Burnt contacts have resistance, and make heat.

    Melting plastic is some sign of overload or resistance in the connection.

    A loose connection on the wiring terminals can cause heat and melt the thing.


    A good properly rated switch should be able to handle a bunch of cycles before it fails. The pump may fail first, before the switch gives out.
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  7. #7
    In the Trades Texas Wellman's Avatar
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    Don I tried the Merrill switches and they melt. I have about a dozen or so left but I refuse to use them. Shame too because the on/off was spot-on wheras the Square D seems to have a lot of variation these days.

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    Moderator valveman's Avatar
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    Quote Originally Posted by DonL View Post
    The problem with a lot of the cheap switches is that the contact plating is no good. Burnt contacts have resistance, and make heat.
    I agree. Except the only time contacts burn is when they make or break. Just means the cheaper the pressure switch, as well as the cheaper the pump, the more important it is to limit the cycling.

  9. #9
    DIY Junior Member mrron's Avatar
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    WOW! This is a great forum. Thanks for all of the suggestions. Let me offer more detail:

    Pump: sta-rite S10P4JP05121 10GPM
    Tank: Flex-Lite FL12 35gallon
    Sprinkler heads: Orbit .8 gpm no more than four on at any one time.

    So if my math is correct a full tank should empty in about 10 minutes. I assume it never really empties. Question is how long does it take for the pressure to drop from 60 psi to 40 psi. No idea! Probably dependent of friction in pipes, orifice size, atmospheric pressure, my mood. Just kidding. But I think you get the picture. I temporarily switched back to town water and the sprinkler heads don't throw the water nearly as far as the well does even though town pressure is 80psi. Go figure. I bought the Square D today on Amazon. I want to buy a backup. Keep the ideas coming.

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    Moderator valveman's Avatar
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    You have a 10 GPM pump and a 32 gallon tank holds 8 gallons of water. So using four of the .8 GPM sprinkler heads is requiring 3.2 GPM. That means your tank is draining in 2.5 minutes and refilling in 1.5 minutes. That is a complete cycle every 4 minutes, 15 cycles per hour, or 360 cycles in a 24 hour day. That can add up to 131,000 cycles per year if left running 24/7. Even a Square D switch can’t survive with that much cycling. You either need to run no less than 13 heads at the same time, or get a Cycle Stop Valve so you can run as few heads as you want without cycling the pump (and switch) to death.

  11. #11
    DIY Junior Member mrron's Avatar
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    I learn something new every day. Didn't realize a 32 gallon tank held only 8 gallons. I installed the Square D switch and it works fine as expected.
    For the first time I examined the pressure during a watering cycle. When the system with 4 sprinkler heads came on the pressure held steady at 58 psi. No recycle. The output of the 4 sprinklers must be more than I expected or the pump is not delivering what I thought. I then ran two systems at once ( 8 sprinklers) and the pressure dropped to 30psi and held steady. The flow pattern of the 8 sprinklers seemed adequate. So I don't see the need to change anything except buy another switch as a backup. Thanks again for the suggestions.

  12. #12
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by mrron View Post
    I learn something new every day. Didn't realize a 32 gallon tank held only 8 gallons. I installed the Square D switch and it works fine as expected.
    For the first time I examined the pressure during a watering cycle. When the system with 4 sprinkler heads came on the pressure held steady at 58 psi. No recycle. The output of the 4 sprinklers must be more than I expected or the pump is not delivering what I thought. I then ran two systems at once ( 8 sprinklers) and the pressure dropped to 30psi and held steady. The flow pattern of the 8 sprinklers seemed adequate. So I don't see the need to change anything except buy another switch as a backup. Thanks again for the suggestions.

    That sounds like the best way to run your system if you get the water distance that you need.

    Please post if you have the same problem using the SD switch.

    They are all getting cheap, but the SD is still made in USA, as near as I can tell.


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  13. #13
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by mrron View Post
    When the system with 4 sprinkler heads came on the pressure held steady at 58 psi...
    If your range is set to 40/60, that is cutting it a tad close. I would up the range to 45/65 or 50/70 so long as the pump cannot deadhead at 70 PSI.

  14. #14
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by LLigetfa View Post
    If your range is set to 40/60, that is cutting it a tad close. I would up the range to 45/65 or 50/70 so long as the pump cannot deadhead at 70 PSI.

    I think it was said that it dropped to 30 and held.

    I could be wrong.

    A CSV may be needed.

    Watering 2 zones at once will save water and power.


    Have Fun.
    Last edited by DonL; 10-04-2013 at 08:42 AM.
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  15. #15
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by DonL View Post
    I think it was said that it dropped to 30 and held...
    Ja, with 8 heads but he said with 4 heads it hovered around 58. I'm guessing he has at least one zone with 4 heads and another with 8.

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