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Thread: Questions on cavitation

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    Questions on cavitation

    Hello, just bought a home and am a new pool owner for a whopping 10 days. Have noticed something that didn't sit well with me and am seeking advise.

    I have an IG ~10,000gal pool w/ two intakes, one being the skimmer, the other being an intake dedicated to the Hayward (its older, looks like the "poolvac classic" though). The skimmer & poolvac line come together to a Hayward valve which allows me to select what enters the pump.

    When the valve is open to just the poolvac, the pump gets significantly louder & PSI drops on the filter. There is also a significant build up on the air (when I turn the pressure release on top it always bleeds air for a while, though air isn't making it to the returns to the pool). When I turn the valve toward just the skimmer (either partially or completely) the "rocks flowing" sound goes down & the sound of flow in the pipes can be heard. When this is the case, the poolvac hardly moves (partially open) or obviously not all all if it is skimmer-only.

    The pool is about 12 years old, taken care of solely by the owners poolguy... Her only advice was leaving it entirely on the poolvac side and never skimming. She was a very "if it ain't broke don't fix it" type & had original filters in the 12 year old cartridge filter as well. What needs fixing? I will pull out the cleaner tomorrow and see if I can get a serial# to see how old the thing is, also inspect the tubing again.

    Thank you so much for your help... I am at much of a loss here.
    11,500 gal IG Plaster finish, CCP420 Cartridge, Superflo 1.5 VS , Swimpure+ / T-15 SWCG, KreepyKrawly, TF-100.

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    duraleigh's Avatar
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    Re: Questions on cavitation

    It is not cavitation......that is a different animal.

    What it is is a suction side air leak. Under certain conditions (by moving the source valve) you are able to create enough resistance on the suction side that air is being sucked into your system.

    There is an article in Pool School that may help you.

    From your description, it a guess but it sounds like the pump lid O-ring may need replacement. You can try pouring water over the lid (pump running) and see if you can stop the air inside the basket.

    EDIT: Rereading your post, it may be a hole in the vac hose that is allowing air into the system.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Questions on cavitation

    I know the hose is rather old (they are in ~4' sections) and recently the previous owner had to throw out a section due to cracking. I will try to poor water over the lid first and see if it helps then grab some new hose. I thought it was strange having to bleed the air out frequently and the valve being wide open on the filter for a good 5-10 seconds prior to water coming out even after the pump running for over an hour.
    11,500 gal IG Plaster finish, CCP420 Cartridge, Superflo 1.5 VS , Swimpure+ / T-15 SWCG, KreepyKrawly, TF-100.

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    Re: Questions on cavitation

    To update. I finally was able to get new tubing, Still having the problem. Was also able to try a different Pool cleaner.

    Seems that the situation only happens when there is resistance on the suction side (as I slowly turn the valve more toward the Poolvac only, air is introduced, if I leave it at 80%poolvac/20%skimmer the cleaner is slower BUT no air problem).

    Also went straight into the skimmer to see if my poolvac line to the pool had a leak, no change.

    To paint a better picture, have to suction lines (poolvac & skimmer) going into a Jandy valve then into the pump. All of these parts are 13 years old, original valve & pump. Previous owner was not very pool-nerdy in taking care of things.

    silicone lubed up the oring to the basket of the pump (no cracks in oring), other than being tough to get on/off looks fine. Jandy Valve has no noticable leaks (went ahead and got $5 oring kit on the way to take that out of the equation).

    Any other suggestions? Thank you so much
    11,500 gal IG Plaster finish, CCP420 Cartridge, Superflo 1.5 VS , Swimpure+ / T-15 SWCG, KreepyKrawly, TF-100.

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    borjis's Avatar
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    Re: Questions on cavitation

    There was a post somewhere that someone had a similar issue and I had that as well.

    It turned out not to be a suction leak...it was the pump being a bit too powerful and needing some suction relief. (or something to that effect)

    There are these adapter/valve things and skimmer plates too, that allow you to dial in the suction so it's not all
    being drawn from the cleaner (mine goes through the skimmer pipe). At the valve dial there is an inlet that lets some of the suction come through that.

    I have a 1.5 hp pump too and had this problem when vacuuming, but found an adapter valve the previous owner
    had placed in the garage. my previous 3/4 hp pump never had this problem.

    with the valve adapter and suction hose hooked up to it (through the skimmer pipe), I got no air bubbles or straining sound from the pump
    and the robot still moves rapidly.

    I would think you could find a sweet spot on your jandy valve since it too is regulating the suction from
    the skimmer and cleaner inlet...if the robot still barely moves then you probably do have a suction leak
    of some kind.
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
    (1.5 HP motor) Raypak PR266AEN (266k btu) gas heater. TF-100 Test Kit.
    Dolphin E10 Cleaning Robot.

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    JoyfulNoise's Avatar
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    Re: Questions on cavitation

    I have a similar setup but a much larger pump (3HP IntelliFlo). I never adjust my 3-way valve so that it is 100% on the suction line. Dedicated suction-side cleaner lines tend to be smaller diameter PVC than the main drains or skimmer. A large enough pump set to draw entirely from a small diameter pipe can easily exceed the flow rate that the pipe can deliver. Once that happens, the pump will start to draw air from the basket (no lid seal gasket is perfect) or from anything along the way of the suction line. My Kreepy Krawly is hooked up using 3-ft segmented vacuum hose and has an inline leaf canister with an o-ring seal. If I set my pump on a high speed and put the pump suction to 100% vacuum, I will start to draw air into the line and the pump will eventually lose prime. I run my suction side cleaner all the time (only take it our during swimming) and my diverter is set so that I get both vacuum movement AND skimmer action.

    As bjoris said, you need to just find the right split between your skimmer and the suction side cleaner to make everything work happily.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Questions on cavitation

    Thank you so much for your answers! I had no idea a pump can, for lack of a better term, "suck too much". I too have a KreepyKrauly as well. Good to know that it isn't something massively wrong. I always thought my pump was a bit much (1.5HP w/ 1.47SF=2.2 THP!) especially for how small the pool was. Obviously with air getting in it makes the pump sound awfully loud (which is pretty loud to begin with being 13 years old!).

    Should I get a new pump someday, will get a ~1.5THP pump instead.
    11,500 gal IG Plaster finish, CCP420 Cartridge, Superflo 1.5 VS , Swimpure+ / T-15 SWCG, KreepyKrawly, TF-100.

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    JoyfulNoise's Avatar
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    Re: Questions on cavitation

    WhisperFlo's are really high head pumps and will make a lot of noise if there isn't sufficient head on both the intake and return side. If it's a single speed then you're wasting a lot of money on electricity. When you are ready for a new pump, get a 2-speed or variable speed pump, you will be much happier.


    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Questions on cavitation

    Quote Originally Posted by JoyfulNoise View Post
    WhisperFlo's are really high head pumps and will make a lot of noise if there isn't sufficient head on both the intake and return side.
    High head pump are designed for high head on the return (pressure) side. They can handle higher head on the intake (suction) but it does not help with the performance or noise. Most pumps do best with less head loss on the suction side.

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    JoyfulNoise's Avatar
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    Re: Questions on cavitation

    Quote Originally Posted by JamesW View Post
    High head pump are designed for high head on the return (pressure) side. They can handle higher head on the intake (suction) but it does not help with the performance or noise. Most pumps do best with less head loss on the suction side.
    That's exactly my experience. I have a 3-HP WhisperFlo on the waterfall and unless I add resistance to the pressure side (in the form of a shutoff valve) and split at least 50% of the water flow to a wall return, the pump will make a lot of noise. I consider it a design flaw on the PB as they should have used a waterfall pump not a WhisperFlo. It's also way more pump HP than what is really needed so it's a huge power waste as it is only a single speed.


    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Questions on cavitation

    Correct, my point was that resistance (head loss) on the suction side does not help. The lower the suction, the better. In fact, a flooded suction where water is pushed into the pump is best.

    A high head pump on a waterfall is a bad choice. A waterfall pump or a variable speed would be a better choice.

    Is your pump a WhisperFlo or IntelliFlo?

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    JoyfulNoise's Avatar
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    Re: Questions on cavitation

    Pool pump is IntelliFlo. Waterfall pump is a WhisperFlo. Waterfall plumbing is completely separate from pool plumbing.

    I agree the WhisperFlo was not the correct pump for the application but that is what the PB installed. At some point in the future, I will likely swap it out for a Pentair waterfall pump. The wall intakes for the waterfall are in the shallow end of the pool ~24" below the waterline. I'd estimate the pump intake is ~18" above the water line. The wall intake is probably 20' to the equipment pad. All PVC is 2" diameter. So the intake head loss is fairly minimal. The pump return side splits at a 3-way valve with flow going to a wall return (located above the waterfall intakes in the shallow end) and flow going to the actual waterfall. The waterfall is at the deep end is probably ~60' to the equipment pad. Again, all plumbing is 2" PVC except for the wall return line which necks down to a standard eyeball return.


    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    banditig's Avatar
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    Re: Questions on cavitation

    To Erroz, this is the valve Borjis is talking about that my keeps krawly came with
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