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Thread: Filter Pressure when using Vac

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    Filter Pressure when using Vac

    I am haveing a problem when running my Haward pool vac. When running the vac the pressure in the filter is about 10lbs. When I switch to the skimmer the pressure is about 20lbs. The problem is my heater cycles on and off when using the vac. I have about 30' of hose to the vac. if I unplug the vac and leave the hose I still only have 10lbs but if I remove the hose the the pressure goes back to 20lbs. Could it be that it just can't suck enough water through the hose? Maybe a larger diameter hose? I get good suction on the vac and it will climb all the way up the wall.

    Thanks.
    28K, IG plaster, Pentair DE Filter, Aqua-Rite swg

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    Re: Filter Pressure when using Vac

    Bet you're starving the pump though. Don't close the drain fully. Just enough for the sweep to work,

    Scott
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    Richard320's Avatar
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    Re: Filter Pressure when using Vac

    Quote Originally Posted by ssmith579
    I am haveing a problem when running my Haward pool vac. When running the vac the pressure in the filter is about 10lbs. When I switch to the skimmer the pressure is about 20lbs. The problem is my heater cycles on and off when using the vac. I have about 30' of hose to the vac. if I unplug the vac and leave the hose I still only have 10lbs but if I remove the hose the the pressure goes back to 20lbs. Could it be that it just can't suck enough water through the hose? Maybe a larger diameter hose? I get good suction on the vac and it will climb all the way up the wall.

    Thanks.
    I believe the problem is that you're lifting the water from a greater depth. It's not as efficient pulling the water up so it has less water to push out, which leads to lower pressure.

    I'm more familiar with automotive pumps, but I'm guessing they work pretty much the same. Electric fuel pumps work much better pushing than pulling, which is why they're usually mounted in the tank. Older fuel injection cars, and I'm thinking specifically of VW and Volvo, often mounted the pump externally but below the tank or at least even with the bottom, so the fuel would flow to it by gravity. Some also used a small low-pressure booster pump in tank just to feed the high-pressure pump.

    I have the same experience as you - my pressure drops about 8-10 psi while vacuuming. Since it comes back to normal and it vacuums fine, I don't worry about it.
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    JasonLion's Avatar
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    Re: Filter Pressure when using Vac

    There isn't a whole lot you can do about this. The change in pressure you observe, and the reduced flow rate, are both natural effects of using a vacuum. The vacuum hose increases the length of the suction side plumbing, which means that more of the pumps energy goes to the suction side of the system than it would otherwise, that lowers the energy available on the pressure side (and thus the filter pressure) and lowers the overall flow rate.

    The one thing you can do is to try and balance the setting you use with the vac so that some water still comes in through the skimmer. The more you can open the skimmer the better, though you need to make sure you don't open it too far, ie are still getting enough suction for the vac to work correctly.
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    Re: Filter Pressure when using Vac

    Yep, you want to make sure that, as Scott said, you aren't starving the pump. Open the line to the cleaner all the way. Then open your drain or extra skimmer, if you have one, just to the point where your vac stops working. Once the cleaner stops going, then start to close the drain just until the point that the vac starts working again and leave it there.
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    Re: Filter Pressure when using Vac

    Thanks guys. I don't see a way to partially open the vac. There is a valve that switches between the skimmer and vac. It's a T so it's either one way or the other. I've tried to attach a picture.

    A second problem, I removed the SWG cell to clean it. There's no shutoff valves on each sode of it so I just turmed the skimmer valve halveway hopeing that would shut it off and the filter backwashed all the DE back into the pool![attachment=1:3mz1t8b6]pump.JPG[/attachment:3mz1t8b6][attachment=0:3mz1t8b6]pump2.JPG[/attachment:3mz1t8b6]
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    Re: Filter Pressure when using Vac

    Silly question, perhaps: Did you make sure the pump was turned off when you cleaned the SWG?
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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    Re: Filter Pressure when using Vac

    I assume your sweep is a Navigator and that it plug into the skimmer. The valve has gate inside about the size of one of the ports on the valve. Note that the handle says off on one side. That is where the gate is. It looks like you have shut the drain. You can partially open that port.

    Next time you want to clean the cell, shut off the pump and put the multiport in the Closed position. This stops water from entering or leaving the tank. Your DE will be sealed in.

    Scott
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    Re: Filter Pressure when using Vac

    The vac plugs into the side of the pool seperate from the skimmer. I turned the valve midway between the 2 sides. The pump was off.
    28K, IG plaster, Pentair DE Filter, Aqua-Rite swg

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    Re: Filter Pressure when using Vac

    Then crack open the skimmer. The rest is still valid.

    Scott
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    JasonLion's Avatar
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    Re: Filter Pressure when using Vac

    Two different issues here.

    The main, multi-way, valve should never be put in-between positions while the pump is running (except possibly in the winter). To service the SWG cell you need to turn off the pump, which will be an electrical switch, not a valve.

    The 3-way valve that controls the skimmer vs vacuum can be put in-between positions, which is something you should try.
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    Re: Filter Pressure when using Vac

    Guys,

    I'm an electrical engineer, I'm not going to run the pump with the valve off. My original question was about the heater shutting off. The only reason I could think of was the difference in pressure between running the skimmer and the vac. The SWG cell was removed with the pump off and the valve in the middle position. I still had the filter backwash into the pool. The only way for this to happen is if the valve does not close completely in the mid position. I thought it was odd that there are no valves to isolate the cell when it removed. Maybe something I'll add. Thanks for all the help.
    28K, IG plaster, Pentair DE Filter, Aqua-Rite swg

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    Re: Filter Pressure when using Vac

    As I said earlier, using the CLOSED position when cleaning the cell will keep the DE in the filter.

    WRT to the heater shutting off, it was due to a low flow condition. Cracking open the skimmer some will allow extra water in to the starved pump. There should still be enough suction to run the Navigator.

    Scott
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    JasonLion's Avatar
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    Re: Filter Pressure when using Vac

    Multi-position rotary valves usually connect everything to everything when the handle is in an in-between position.

    The SWG cell is typically left in place, except for a quick visual check and/or cleaning while the pump is off. You don't normally need to close any valves to do that, just turn the pump off, remove the cell, replace the cell, and turn the pump back on. If you do want to run the system with the SWG removed, you will need to replace it with a straight piece of pipe with the appropriate unions on it. If you look around on the Internet you might be able to find an appropriate piece of pipe designed for that purpose. The system will not work correctly if you close off the pipe where the SWG cell is using valves.
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    Re: Filter Pressure when using Vac

    Looking at the picture you posted, you have 2 sources to draw water from, the skimmer and the vac. IMHO, you should never have that valve 100 % to the skimmer or the vac(unless you remove the vacuum from the pool). If you do and your source gets partially clogged or worse, you risk running the pump dry. You need to turn the valve from full skimmer to the point where your cleaner works normally, but no more than that. Then mark the position, so you know where to turn it to the next time you need to set it.

    Quote Originally Posted by ssmith579
    When running the vac the pressure in the filter is about 10lbs. When I switch to the skimmer the pressure is about 20lbs. The problem is my heater cycles on and off when using the vac. I have about 30' of hose to the vac. if I unplug the vac and leave the hose I still only have 10lbs but if I remove the hose the the pressure goes back to 20lbs. Could it be that it just can't suck enough water through the hose? Maybe a larger diameter hose? I get good suction on the vac and it will climb all the way up the wall.
    When you remove the hose, the vac-lock cap closes off the port, so you're only drawing from the skimmer again at 20 lbs.

    For the most efficiency, set the valve midway so you draw 50% from the skimmer and 50% from the vacuum. At that position, I'm guessing that your pressure will be lower than 10 lbs.
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    Re: Filter Pressure when using Vac

    Thanks, I'll try the valve at the mid position. I assumed that both we shut off in that position. I had to take the cell out to clean it. There was a fair bit of buildup. I got most of it out but cut the cleaning short when I noticed all the DE in the pool. Guess I'll have to cap off the pipe when I want to clean the cell or do it when I backwash the filter.
    28K, IG plaster, Pentair DE Filter, Aqua-Rite swg

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