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Thread: Water hammer when vacuuming?

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    Water hammer when vacuuming?

    I recently installed a 2 speed pump and have noticed when I'm done manually vacuuming and turn the pump off there is a noticeable "thump" sound coming from somewhere between the pad and the pool. I can also "feel" the thump somewhat.

    I tried going from high speed to low speed to see if that made a difference and it still makes the noise. It only happens when vacuuming, not during normal operation.

    My psi is normally around 18-19 psi and drops to 13 while vacuuming on high speed. The two suction lines are 2 inch pipe and one return is 2 in and the other is 1.5 in.

    Any thoughts on what the noise could be?
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    Re: Water hammer when vacuuming?

    Do you have a fitting like the Pentair*GW9530*Vacuum Port Fitting?

    It could be that shutting. Otherwise, it sounds like it could be a check valve.

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    Re: Water hammer when vacuuming?

    No, I put the end of the vacuum line directly into the bottom of the skimmer. I don't use a vac plate. Bad idea?

    The noise is fairly jarring. I don't want to crack any lines, etc, thus the concern. Then again, I don't know what I can do about other than go back to a weaker pump.
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    Re: Water hammer when vacuuming?

    You should always use a vac plate. Otherwise, the line can get clogged.

    I suspect that a check valve is shutting. Do you have any check valves in the system?

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    JasonLion's Avatar
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    Re: Water hammer when vacuuming?

    Using the hole at the bottom of the skimmer is fine. You thump can't be related to that.

    An SVRS system would make a thud if it triggered. An SVRS is a special valve that lets air into the system when someone is stuck on a drain cover. They are fairly rare however.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Water hammer when vacuuming?

    If you are drawing a vacuum and shut down a pump you can cause a water hammer as the water floods back through the now stopped pump. But if the flow is that restricted during vacuuming the pool then you don't need to have it on high speed. Having it on the lower speed before shutting down should also reduce the water hammer.
    chiefwej
    Tucson, AZ
    16x36 rectangular (19k) Pebble Tec play pool/spa, Pentair Intelliflo VS 011018, Super II 2hp (spa), Aqua Rite T-15 SWG, Pro Grid 60 DE, Hayward H400 & Heliocol Solar heating, A&A infloor system, fill water w/high CH and TA, 50 ppm borates,TF-100 test kit

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    Re: Water hammer when vacuuming?

    Is it possible to vacuum on low speed?

    I've started going down to low speed before shutting off the pump.

    I think I made a mistake going with this pump. I tried to match the total horsepower of the old starite because i have a spa, but it seems substantially more powerful. It may even be too much for my cartridge filter. I'm noticing more dirt bypassing the filter while I vacuum.

    Should have gone a half horse lower.
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    Re: Water hammer when vacuuming?

    Do you have any other intakes besides your skimmer?

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    Re: Water hammer when vacuuming?

    I believe ther is a spider valve on the suction lines where they converge at the jandy automatic valve.

    - - - Updated - - -

    There is a spa drain (two of them) and the main drain.

    At the bottom of the skimmer there are two holes. Am I correct that one of them comes from the main drain?

    There are two suction lines at the pad.
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    JasonLion's Avatar
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    Re: Water hammer when vacuuming?

    A lot of skimmers have two ports in the bottom, with one of them sealed off just below the skimmer.

    If you have two suction lines running to the equipment pad, they are almost certainly main drain and skimmer(s). When the main drain is plumbed to the skimmer there is never more than one line to the equipment pad.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Water hammer when vacuuming?

    Come to think of it, the pool tech replaced a spider valve on the suction line side when he replaced the pump, because the spa was losing about 6 inches of water overnight.
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    Re: Water hammer when vacuuming?

    Do you change any valves when vacuuming?

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    Re: Water hammer when vacuuming?

    Quote Originally Posted by stebs View Post
    Do you change any valves when vacuuming?
    No. This is a new issue that started with the installation of the pentair pump. It's a bit disconcerting. I'm going to try and localize the thump with the help of my wife.
    11,000 gallon in-ground pool/spa combo, pebble-tec, Sta-rite system 3 cartridge 300 sqft, Pentair Whisperflo WFDS-6 2 speed 1.5 HP full-rated, formerly Starite Max-e-Glas 2 HP up-rated single speed, Sta-Rite Max-E Therm natural gas heater. Jandy Aqualink RS Onetouch. Manual vacuum. Chlorine.

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    Re: Water hammer when vacuuming?

    I changed my pump to a new high efficiency Pentair VS. I have noted that if I'm running it at a higher speed it will thump when shut down unless I change to a slower speed first.
    chiefwej
    Tucson, AZ
    16x36 rectangular (19k) Pebble Tec play pool/spa, Pentair Intelliflo VS 011018, Super II 2hp (spa), Aqua Rite T-15 SWG, Pro Grid 60 DE, Hayward H400 & Heliocol Solar heating, A&A infloor system, fill water w/high CH and TA, 50 ppm borates,TF-100 test kit

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    JasonLion's Avatar
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    Re: Water hammer when vacuuming?

    Have you let all of the air out of the filter? Or does air accumulate in the filter each time the pump is run?

    Hopefully this isn't it, but it could be that you are running the pump at too high of a speed, and the filter is deforming, with a thump when the pump goes off and it returns to it's normal shape. If so you would definitely want to turn down the max speed setting.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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