pump suction problem

since i suspect someone else might have run into this problem, i'm posting it here:

i replaced a pump motor a couple weeks ago (hayward maxflo 1hp) cuz the bearings were squealing.  but since then a mysterious problem has persisted: the system won't come up to pressure as in the pump doesn't seem to be moving the volume of water it's supposed to.  i checked the impeller and it's on tight (did replace it a couple years ago), and it doesn't seem anything is obstructing the suction or discharge side.  i went out to troubleshoot, and after taking the pump apart 'n putting it back together to test it three times, it finally all worked just fine.  the only variable is possibly the diffuser gasket had gotten incorrectly positioned but was corrected the last time.  but now a week later, the customer has called to report that once again, after functioning well for a week, the pump is again not bringing the system up to pressure. 

any ideas???

thanks for any suggestions!!


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  • How bout Pressure test the suction line and see if there is a problem with the line.  Also a little silicone on the male adapter at the pump suction side would let you know if there is a problem there.  One more thing, make sure the Winter Plugs are tight and have teflon on them.  I have seen a crack at the drain plug on this model pump several times before and putting some silicone around the plug area temporarely repaired the problem.


    One other thought, if the sand needs changed and is very old and loaded up.  The Pump will start ok but load up due to back pressure and eventually start cavitating itself due to the load on the pressure side.  Run this pump on recirculate for a day and this will tell that story.


    Good Luck


    Alan Matheny

    Morehead Pools


  • What a waste of time and effort how you  ever put a man on the moon beats me. 

    Next time dont stuff  around put in a new Pump and Motor that way you make some money.

    Kiwi Norman www.poolquartz.co.nz

  • clint - that's just what the aosmith tec guy said, so i guess i've exceeded my understanding, and hit a dead end in that theory.  i'm ready to go for a new motor if i get that 'breaker trip' again.

    david - that's what i thought too, so i mentioned it here for brighter minds than mine to clarify.

    tc - that's right, there is a reset button on one of the breakers. (U2)

    brian - yes, when the motor was replaced 4+/- weeks ago, i also replaced the seal.  the challenge with any attempt to isolate and test for any up or down stream blockage is that if it exists, it is intermittent (=most times no restriction is present - full flow is demonstrated)

    btw:  i got called back again today, with the same complaint of 'lack of pressure' on the filter gauge.  when i attempted restart of the motor, sure enough, despite suction air leaks, it eventually primed and came up to pressure.  he mentioned a "whoosing" sound when he turned off the motor which i'm certain is the 'reverse release of air pressure' captured in the sand filter tank (tr60 type with side valve).  but it also raised in my mind the possibility of a near total water blow out in the pump such that, without re-priming, there might not be enough of a reservoir of water to allow the pump to re-establish prime/flow.  when i asked if the lack of filter pressure came about in the middle of normal circulation, he couldn't answer for sure, but instead said, after manually starting the pump in the morning and going for his latte, when he returned there wasn't any filter pressure.  so now we're working on the theory of an air-leaking suction frustrating the initial priming process as the cause of his 'lack of filter pressure' (=the system never established prime/flow!!)  and we'll leave the other electrical irregularity for it's next occurrence, and then run the aosmith tech guys test on supply amperage when it makes that mild short noise, and take a closer look at the start switch inside the back cover plate.

    i sure appreciate you all for your invaluable observations!!!!  can't thank you enough!!

    wishing you all clear water and a clear heart!!


  • Wes did you try a new pump seal? It sounds like everything else has been checked. We had a simular problem and it was a small slit in the rubber seal under the spring. If you think it may be a restriction in the suction line a vac gage will tell you if you have a problem there.
  • God bless you.................. your going to have your reset button on one side or the other on a 220v breaker........
  • "Double Poll 230 breaker (with one half GFI-ed)"


    I'm not an expert on electrical, BUT I don't think this is proper, and I'm wondering if it could be the cause of the problem...

  • If "half" of the breaker trips off, you will not have low power to the motor, you will have an open circuit and the motor will not run at all. 

    After reading your comment about the motor trying to start but sounding like a dead short then tripping the breaker and then later working fine, I bet that you have a shorted spot on the start windings. If that spot lines up wrong, the motor will not start as you observed. But, if you turn the shaft slightly, it will start and run fine.

    If this is the problem, you need a new motor.

  • hi guys,

    sorry but i'm not up to speed enough to upload a video to youtube and then link to it here ... but i did get one today when i went back.  it shows an attempted start, but a half hearted 'dead short' sound mixed with an attempted cap. start.  the motor eventually tripped the breaker in subsequent attempts to start the pump.

    so i went back to the drawing board and restarted a thorough examination, from the tail end (all wire connections look solid with no shorts or bare wires).  then i took the motor apart and o-rings and seals where in place with the diffuser correctly positioned (no wear ring present).  the impeller was tight and smooth turning and unobstructed.  frankly, all looked well.

    so i put it all back together, filled the pot and attempted a restart .... and it fired off as smoothly as you'd want a motor replacement to go, primed eventually, and then ran just as it was supposed to do, coming up to full pressure.  but that's now the second time i've been through this only to have the customer call back in a week complaining of "no pressure", which is why i wrote this question in the first place.

    so, since the flow/pressure was satisfactory, the possibility of a 'moving' obstruction, while still viable, increasingly seemed remote.

    instead, it seemed to me the source of my problem had to be electrical, as in a bad motor, or a bad breaker.  the pump is running on a double pull 230 breaker (with one half GFI-ed!), and since the breaker was tripped during my initial attempts, there had to be some irregularity electrically.  i don't know if it makes a difference, but the two legs of power were 118.5 and 116.4.

    i've got a call into AOSmith tech support to see if they can guide me in isolating a rationale for the breakers tripping, but i'm convinced that half of the breaker is tripping off, thus reducing the supply to the pump and resulting in "no pressure"  because the "no pressure" complaint was present even before i changed the motor; we had just assumed the bearing noise was involved in the problem.

    thanks again to all of your for your tips; it really was a help as i worked through all the options and you helped me cover all the bases!! 

    blessings to every one of you!!


    TC Smith said:

    post a video on you tube..............and let us take a look  It could be a lot of different things, but you post a video and someone is going to see or hear something that is not right............
  • Uhm, Is the filter dirty? I know I have overlooked the obvious on many occasions.


  • One other thought that could cause an intermittent suction / flow problem. Do you have a check valve on the system? The flapper in a check valve can come loose. If it does, there will be times that it allows flow and times when it blocks the flow.
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