Jet pump rapid short cycling at cut-out

Discussion in 'Pumps and Tanks Well Forum & Blog' started by FRS, Apr 28, 2013.

  1. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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. craigpump

    craigpump Well-Known Member

    Messages:
    1,081
    Location:
    ct
    There is a loss of pressure someplace most likely at the footvalve
  3. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    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. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    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. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    A bad valve or obstructed line on the discharge of the pump will cause the problem you're having.

    John
  8. craigpump

    craigpump Well-Known Member

    Messages:
    1,081
    Location:
    ct
    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. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    554
    Location:
    SE Texas-Coastal
    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. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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: Apr 29, 2013
  12. craigpump

    craigpump Well-Known Member

    Messages:
    1,081
    Location:
    ct
    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. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    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. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,511
    Location:
    Houston, TX
    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.
  15. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    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.
  16. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    just a question....why does that explain why it is cutting in at 40 when it should be cutting in at 20....am i right that anything in between should make no difference to the switch and, ultimately, the pump until it gets down to 20?
  17. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    You missed the explanation where the switch was not crossing the point of no return. Why not take the cover off the switch and watch it.

    Those switches are not marvels of engineering precision. They are also not designed to be mounted far from the tank. It might also have some sediment trapped under the diaphragm.

    Abandon the one mounted on the pump and wire in a new one at the tank.
  18. FRS

    FRS New Member

    Messages:
    11
    Location:
    toronto
    ah ha! sediment. I don't think we have a location issue....never have before.

    granted, it was 10:30 at night so I didn't take the cover off the switch but sat on a rock pointing a flashlight at the gauge and watched it for half an hour. pretty well precisely every minute or so it would cycle....sat at exactly 40 lbs the whole time (except when it cycled of course) with no demand on the system....it was like it just felt like doing it. trust me, i've been around the block a few times with pumps....this one is just really strange.
  19. craigpump

    craigpump Well-Known Member

    Messages:
    1,081
    Location:
    ct
    If there is no demand for water and the pump is cycling that tells me there is a pressure loss someplace.
  20. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    That description suggests that there are pressure pulses brought on by having the tank too far from the pump. The pressure pulses cause the contacts to bounce open and close. A waterlogged tank can present a similar symptom.

    That also suggests a switch that now does not latch open when it should. There is a fine balance point where once the contacts open, it should cross the point of no return, latching open until the pressure drops to 20 PSI.

    The fact that a minute later the cycle repeats is another symptom which suggests that either the pump went into thermal shutdown for the minute, OR there is enough of a pressure drop for the unlatched contacts to close.

    Sediment in the nipple can affect switch behaviour in a broad way. Sediment under the diaphragm usually affects the low pressure kick-in side of the operation.

    As I suggested before, abandon the switch on the pump and install a new switch at the tank Tee where it belongs.
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