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Thread: pump running away??

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    pump running away??

    Okay I'll do my best and try to explain this. I just put in an Jandy Epump 1.5 and first I thought I had a suction side leak but now I think it is something else. When the pump is in the off position I do not lose prime. The water level stays just below the plastic sight gauge. When the pump is running at full speed the water is very turblent for a whyle but when I slow it sown I start to see the water level in the pump starts to go down. It looks like it is pumping out more water then it is taking in. Any ideas whey this is happening and do you have a solution. Thanks

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    Re: pump running away??

    Sounds like cavitation. Have you tried opening your skimmers and your main drain all the way to see if that helps it?
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    Re: pump running away??

    If it is cavitation, what is causing it and how do I fix it?

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    Re: pump running away??

    If your pump is cavitating, it means that it is starving for water on the suction side. It can be resolved oftentimes by allowing more water flow to the pump from the suction supply sources.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Re: pump running away??

    If you have 1.5" plumbing everywhere, you will need to make a 2" manifold and feed the 1.5" lines into that and then use 2" to the pump. Can you post a picture or two of your existing equipment pad so we can see the plumbing?

    Scott
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    Re: pump running away??

    I would eliminate a suction side air leak as the cause before I tried to solve a cavitation issue.

    I have never seen a pump cavitate but a description I have read says that it will occur at the impellor and (it seems to me) would not show air in the pump basket as a result.

    What you are describing (unless I am overlooking something) appears to me that air is getting into the system somewhere between the skimmers and the pump. It is very possible to have that leak and still maintain prime when the pump is off. Once the pump turns on, low pressure is created on the suction side and allows the leak to let in air.

    There is usually a leak somewhere in the pumbing as it emerges from the ground and goes to the pump. If that's not it, often the pump basket lid is sealed incorrectly and allows air to enter. There are also some drain plugs at the bottom of the pump strainer basket that can be loose and allow air in.

    Find that air leak and your issue will be solved, I think.
    Dave S. - Forum owner
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    Re: pump running away??

    duraleigh is probably right. Also, cavitation makes a lot of noise. An air leak doesn't.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: pump running away??

    Cavitation will show air in the pump basket. Cavitation occurs in the water primarily. However, your pump will not cavitate more when the pumps rpm's drop. The large pot basket on the Jandy pumps are notorious for this. I have yet to see one "glass over" and run with a full pot. If you're not convinced, install a vacuum gauge and observe the the amount of vac. If it is less than 15 in Hg, you're probably not cavitating. Also, the idea of these energy pumps are to run them at a lower rpm/flow, and longer run times, so increasing the pipe size is not necessary.
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    Re: pump running away??

    Cavitation is the vaporization of water which is effectively boiling and that can only occur at very high temperatures and/or very low pressure. At sea level and 80 degree water, cavitation will only occur at suction higher than 29" hg! You can only get that type of suction right at the impeller. Also, the bubbles do not survive very long because as soon as the water pressure rises above 29" hg, the bubbles collapse. It would be nearly impossible to have that type of suction in the pump basket itself. For residential pool pumps, cavitation rarely occurs and when it does, it only happens right at the impeller and usually with very high HP pumps. Also, cavitation is heard much more often than it is seen.

    Often the air seen in pump baskets is not cavitation but just air being sucked into the pump basket. Again, with residential pool pumps and plumbing, the seals are not all that tight so air leaks will occur well before cavitation occurs which is why it is often mistaken for cavitation.

    Here is a very good article on cavitation.

    Also, a video of an open prop cavitation. Notice how the bubbles stay very close to the prop. Unfortunately, you can't video a closed impeller but the bubbles tend to stay inside the impeller.

    One more point to add. When there is any flow rate through the pump while it is cavitating, the cavitation bubbles will tend to get pushed through the impeller to the return side where they will quickly collapse.
    Mark
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    Re: pump running away??

    Thanks for coming by guys! I wasn't 100% sure about the cavitation issue or not and I'm learning a lot for what it's worth.

    The reason that I thought that is because my pump does cavitate if the valves are limiting the flow from the suction side to a certain degree. It is loud when this occurs (you can hear it from inside the house) and is immediately resolved by opening any valve up a little more.
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    Re: pump running away??

    The sound of cavitation is very distinctive. Sort of like pumping gravel. However, if the pump is just sucking air, that can make a bit of noise too though not nearly as loud as cavitation.

    The main point is that air in the pump basket does not mean there is cavitation it just means that the pump is sucking air from somehere. Cavitation may still be occuring but generally, the pump will suck air long before cavitation occurs. Also, it would be very unusual to have cavitation without the pump sucking in some air because the seals are not designed for such high suction that occurs with cavitation.
    Mark
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    Re: pump running away??

    Welcome to TFP!!

    First place I'd look is the skimmer to see if the weir is stuck up and that the basket isn't congested.

    Please keep us posted with how you're making out with this.
    Luv& Luk
    -Ted

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    Re: pump running away??

    You can see the air assosiated with cavitation in the pot basket! I know this because i have see it. It's not the type of air that drains out the pot, but more like hazy or cloudy water. In bad cases, small bubbles. One way to find out if the air is from cavitation is that if you watch though the pot lid and turn the pump off, the air will instantly disappear.
    Cavitation can, and does occur in even 1/2 Hp pumps. It's not just limited to big commercial pumps. All that you need is a good blocked, or restricted suction line to get it. I will agree that the sound is distinctive, like someone threw some gravel into the pump.
    I'm not trying to argue or disagree with anyone here, I just wanted the OP to know that this condition can exist, in most any pool pump, and how to recognize it.
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    Re: pump running away??

    Pool Clown,

    I believe what you are seeing is the dissolved air in the water outgassing under low pressure. This is very similar to what happens right before water starts to boil or vaporize. At sea level, water will vaporize at 212 deg F. However, air bubbles will form well below this temperature due to air outgassing. The air cannot remain dissolved at higher temperatures and/or lower pressure since solubility depends on both temperature and pressure. However, this is not the same as reaching the vapor pressure of water. So outgassing can occur even if cavitaion does not. With outgassing the bubbles would form with the pump on in the pump basket but disappear (i.e. redissolve) when the pump is turned off. Outgassing is still a condition of high vacuum and high suction head loss but it is not as bad as cavitation.

    Again, air bubbles in the pump basket can be caused by several factors and are not an indicator for cavitation. The best way to determine if cavitation is occurring is by the sound of the pump. In a pump, when cavitation does occur, the air bubbles are pushed outwards along the impeller and collapse very quickly so you would never see the bubbles in the pump basket but you will see the outgassing bubbles during cavitation so that is why it is often sited as a indicator for cavitation when in fact it is not. Outgassing can occur without cavitation but cavitation is usually accompanied by outgassing.

    The deaeration process is described in this link.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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    Re: pump running away??

    Hey Guys, Thanks for all the grate advice. I do not think it is caveating as the water level goes down in the pump basket at a lower RPM and runs just fine at max RPM. I can't seem to find a leak anywhere. When I shut the pump off I don't see any water coming from any visible couplings. When the pump sits over night the level in the pump basket goes pretty low. Low enough below the suction intake. I have noticed that at low speed the filter runs at 4-5lb and at medium speed it runs at 10+ lbs. At the medium speed I have noticed the pump seems to keep better on the suction side. I am at a loss

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    Re: pump running away??

    Quote Originally Posted by mas985
    Pool Clown,

    I believe what you are seeing is the dissolved air in the water outgassing under low pressure. This is very similar to what happens right before water starts to boil or vaporize. At sea level, water will vaporize at 212 deg F. However, air bubbles will form well below this temperature due to air outgassing. The air cannot remain dissolved at higher temperatures and/or lower pressure since solubility depends on both temperature and pressure. However, this is not the same as reaching the vapor pressure of water. So outgassing can occur even if cavitaion does not. With outgassing the bubbles would form with the pump on in the pump basket but disappear (i.e. redissolve) when the pump is turned off. Outgassing is still a condition of high vacuum and high suction head loss but it is not as bad as cavitation.

    Again, air bubbles in the pump basket can be caused by several factors and are not an indicator for cavitation. The best way to determine if cavitation is occurring is by the sound of the pump. In a pump, when cavitation does occur, the air bubbles are pushed outwards along the impeller and collapse very quickly so you would never see the bubbles in the pump basket but you will see the outgassing bubbles during cavitation so that is why it is often sited as a indicator for cavitation when in fact it is not. Outgassing can occur without cavitation but cavitation is usually accompanied by outgassing.
    I thought that was pretty much what i was trying to relate. Only in a simpler explanation.
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    Re: pump running away??

    Sorry, I was just trying to make the distinction between cavitation and outgassing as they are two completely different phenomenon that sometimes occur together but not always.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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