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Thread: Jet pump rapid short cycling at cut-out

  1. #1
    DIY Junior Member FRS's Avatar
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    Default Jet pump rapid short cycling at cut-out

    My jet pump (1/2hp) has started cycling very rapidly at the cut-out (40psi). Cycles perhaps 4 or 5 times in the space of a few seconds...pressure guage fluctuates rapidly with it and then shuts off and sits happily at 40psi. It will do this every minute or so without any demand in the system. Lights in the cottage flicker wildly and the pump gets, of course, quite hot until it shuts itself completely down, cools off and starts doing it again.

    New 25 gal pressure tank last summer. 18psi charge in it.

    Cut in on the motor is 20.

    New pump last summer.

    No leaks anywhere.

    Foot valve is ok.

    There is no check valve on the system.

    We're pulling water from the lake (cottage system).

    I started the system up this past Thursday (today is Sunday) with no issue (had everything running in 10 minutes flat). I winterised the pump properly....poured plumbing antifreeze directly into it as I do every fall. Rest of the system I blow out. Anyway, it started cycling on Saturday. Normal cycles have been the 2 to 3 min range...normal in my opinion.

    Wondering one of two things....
    1) the pump is about 135 ft away from the panel....running 14/2 wire. Am I getting too much resistance? But if this was the case why would it cycle like this only at the cut-out. I have noticed that this pump does dim the lights very briefly when it cuts in where the old pump didn't (we burnt out the old pump because the tank failed....don't ask!)
    2) at every start up in the spring it does take a day or two to have the water come "clean" and not be spitting up dirt etc. after I drop the foot valve back in the lake. Has there been some grit hurt the impeller or better yet, the pressure switch.

    Any ideas out there before we go back up this weekend? I really don't want to be buying a new pump!

    Thanks!

  2. #2
    DIY Senior Member craigpump's Avatar
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    There is a loss of pressure someplace most likely at the footvalve

  3. #3
    DIY Junior Member FRS's Avatar
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    Thanks. I did pull the intake out of the lake and checked....no leaks or obstructions on the foot valve and there are no leaks anywhere in the system. Pressure does not dip from 40 before the pump decides to bizarrely cycle...but as I describe, the pressure then swings wildly as it quickly cycles. And besides, if there was a leak, the pump should be waiting to dip to 20 for it to cycle.

  4. #4
    DIYer, not in the trades LLigetfa's Avatar
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    Where is the pressure switch in relation to the bladder tank? It sounds like there is too much distance between them. It also sounds like the tank is getting waterlogged so maybe a busted bladder.

    As for losing pressure when no water is used, that can only be a leak or footvalve issue.

  5. #5
    DIY Junior Member FRS's Avatar
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    75 feet away and 15 feet vertical. Has never been an issue.

    Tank is brand new and reads 18 lbs. Trust me, aside from leaks that's the first thing I checked. Again, the system is NOT losing pressure. Therefore no leaks. And, I have checked the entire system for leaks.

    Silly thing just spontaneously turns on and off and on and off and on and off and on and off (say that reallllly fast and you'll get a sense of what I'm talking about) every minute or so at 40lbs pressure and no demands on the system.

  6. #6
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by FRS View Post
    75 feet away and 15 feet vertical. Has never been an issue...
    Just cuz you got away with it this long doesn't make it right. Move the switch up to the tank Tee where it belongs. There is probably some sediment in the line somewhere or at the tank Tee letting the pressure build up faster than the tank can take it.

    Also, a bladder can be bad and it still hold pressure. A drawdown test would be required.

  7. #7
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    A bad valve or obstructed line on the discharge of the pump will cause the problem you're having.

    John

  8. #8
    DIY Senior Member craigpump's Avatar
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    That's true John especially if there is some galvanized pipe in there.

    Like someone else said the pressure switch needs to be at the tank.

  9. #9
    DIY Junior Member FRS's Avatar
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    no galvanised. black water line, pex and copper (hey, it's a cottage)...moving to all pex however. no obstructions....water flows at pressure and volume the way it always has. it's just the silly thing is cycling rapidly at it's cut out.....had cycling before at cut in which makes sense for a variety of reasons.

    question....how do you install a pressure switch 75 ft away from the pump? respectfully guys (i really appreciate your feedback) pressure is pressure and what difference does it make if the tank is a foot away or 75?

  10. #10
    In the Trades Texas Wellman's Avatar
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    Put a small tank just after the pump and see if it dampens the cycling. I've also seen a "snubber" valve at the pressure switch. What has happend is that when the pump comes on the pressure increases just momentarily to kick the switch out, and then the pump kicks off, and then back on. If you dampen the pressure by adding a 2nd in-line tank it will help. Either that or move the switch and wires.


    More than likely something has gotten into the plumbing that causes just enough of a restriction at the outlet line or pressure switch nipple to cause the cycling. If you can clean this out then you should be good to go. Did you take apart the pressure switch nipple?

    Good luck.

  11. #11
    DIY Junior Member FRS's Avatar
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    Texas....this is actually what I'm thinking. I think some dirt has got into the nipple and is playing games with the switch (just my thought in the recesses of my brain). I haven't taken it apart yet (had wife and children there on the weekend....didn't want to mess with it if you understand what I mean).

    and by the way.....dishwasher inlet valve (yet something else to take apart)....water is trickling in....i believe the screen is clogged....a lot more particulate in the water this year as we've had very high water and flooding.

    However, you do say "when the pump comes on". This is the thing....it shouldn't be coming on at 40psi, right? I could understand if this was happening at the cut-in at 20.
    Last edited by FRS; 04-29-2013 at 02:28 PM.

  12. #12
    DIY Senior Member craigpump's Avatar
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    Actually it's pretty easy to install the pressure switch on the tank. Find a place to install it, run the wire going to the pump over to the switch and then run another piece of wire from the switch to the pump.

    You didn't say what make of jet pump it is, but a cast iron pump will develope rust and scale inside that will create blockages in the small ports used for pressure switches and gauges.

  13. #13
    DIY Junior Member FRS's Avatar
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    alright, down the cliff,,back up the cliff...etc. etc. (3 yr old and 6 yr old and wife looking at me like I'm mental all at the same time.....)

    a.o. smith built for Home Hardware. i installed it end of september last year so not so sure about the rust question.

    ok, ok, I hear "warranty" from you....would really like to know what's going on though!!

  14. #14
    Jack of all trades DonL's Avatar
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    Sucking from a lake may have just sucked up a fish.

    I see fish in some strange places.

    Remove the fish parts from the pressure switch and put a better filter in the water inlet to the pump.

    Your jet may be plugged also. Make sure that all of your water shutoff valves are fully open, and that your jet is making pressure.


    Good Luck.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  15. #15
    DIYer, not in the trades LLigetfa's Avatar
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    I don't know if you're up for a physics lesson but you seem to set in your ways as to what physics you think are at play.

    A jet runs on a bit of a modified curve. They use pressure to create volume, so as the pressure goes up, so too does the volume up to a point. The increased volume causes higher pressure at the pump than at the tank... line resistance... high enough for the pressure switch to start to open, but as the tank is still absorbing volume, it drops before crossing the point of no return. Because it did not cross the point of no return, it can turn back on without it having to reach the low pressure setpoint.

    Move the switch up to the tank Tee where it belongs, or as the Texan said, put a small tank at the pump.

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