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Thread: Repeated hammer/knock of solar when pump starts

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    Repeated hammer/knock of solar when pump starts

    Strange problem has developed this year... when the pump comes on in the morning (and the solar panels are NOT selected), the pipes up to the solar panels knock/hammer about once or twice a second for several minutes, then settle down. I can't figure out what could possibly be causing it. Thoughts?

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    Mod Squad jblizzle's Avatar
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    Re: Repeated hammer/knock of solar when pump starts

    You seeing air from the pool jets?
    Could the check valve on the solar return not be sealing?
    Jason, TFP Moderator
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    Re: Repeated hammer/knock of solar when pump starts

    There really isn't much air coming out, but since the supply side valve seems ok the return check valve is indeed the obvious suspect. I've uploaded a video that shows the source side and then the return check valve, and then shows what happens when the pump is turned on (with solar not selected) at Pool solar issue - YouTube

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    Mod Squad jblizzle's Avatar
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    Re: Repeated hammer/knock of solar when pump starts

    That is quite interesting. I have not seen anything like it. Hard to make out the plumbing layout from the video, but looks like the solar valve is actually turned on? Do you also have shutoff valves on the solar lines?
    Jason, TFP Moderator
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    Re: Repeated hammer/knock of solar when pump starts

    Your video points at that check valve.......is that where the noise is coming from?
    Dave S.
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    Re: Repeated hammer/knock of solar when pump starts

    Plumbing setup is: pump to sand filter. Sand filter output goes to the solar valve, which in the video is off, so water then flows to the solar return T and then the gas heater and back to the pool. On the solar side of the return T is a spring check valve. No shutoff valves on the solar lines... they run about 50 feet underground and then up to a first story roof with two banks of panels. At the top is a vacuum relief valve.

    When the solar is on, there's no noise made, the solar fills and heats the pool. When the pump shuts off, the solar drains back and the vacuum relief operates.

    When the solar is off, there's immediately the knocking sound and lots of vibration in the return line... so my only guess is that the spring check valve on the return is busted and the solar is filling via that but air also needs to come back that way, causing the knocking. I think the next test is to try to get a ladder up to the top of the panels so I can pop off the vacuum relief and turn on the pump and see if they're filling. Unless someone has a better idea...

    - - - Updated - - -

    Quote Originally Posted by duraleigh View Post
    Your video points at that check valve.......is that where the noise is coming from?
    The noise is from the entire return line. There's visible motion at the check valve and then at the other end of the underground run, where the return side slaps against the side of the building all the way up.

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    mas985's Avatar
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    Re: Repeated hammer/knock of solar when pump starts

    Is the clear check valve between the filter and solar valve opening and closing in rhythm with the noise or is it staying open?

    Is the filter pressure bouncing up and down too?
    Mark
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    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Repeated hammer/knock of solar when pump starts

    Quote Originally Posted by mas985 View Post
    Is the clear check valve between the filter and solar valve opening and closing in rhythm with the noise or is it staying open?

    Is the filter pressure bouncing up and down too?
    Clear check valve on the supply side (before the solar valve) stays open, very very slight movement in time with the noise. Filter pressure is going up and down very slightly with the noise.

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    Re: Repeated hammer/knock of solar when pump starts

    At this point, I would probably check the vrv. If that is not opening, the compressed air could be causing the oscillation. But that might mean the return check valve also has an issue.

    Is your solar valve a true solar valve or a regular valve with a hole drilled in it? If that does not seal, it could be contributing to the problem.
    Mark
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    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Repeated hammer/knock of solar when pump starts

    Quote Originally Posted by mas985 View Post
    At this point, I would probably check the vrv. If that is not opening, the compressed air could be causing the oscillation. But that might mean the return check valve also has an issue.

    Is your solar valve a true solar valve or a regular valve with a hole drilled in it? If that does not seal, it could be contributing to the problem.
    Vacuum relief valve at top of panels is operating normally... opens and allows air in when the panels are draining, stays shut and doesn't leak otherwise.

    The solar valve is a jandy 3-way valve, no modifications.

    So far the best guess is that the return check valve isn't working right... a (better) replacement has been ordered... until that gets here I don't want to cut the existing one out to look at it.

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    mas985's Avatar
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    Re: Repeated hammer/knock of solar when pump starts

    Does the vrv allow air out when solar is off and the pump turns on?
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Repeated hammer/knock of solar when pump starts

    Quote Originally Posted by mas985 View Post
    Does the vrv allow air out when solar is off and the pump turns on?
    I don't believe so, but with so much racket when that's going on I'd need to climb up on the roof to verify that.

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    Re: Repeated hammer/knock of solar when pump starts

    I've seen similar issues before and usually a new check valve on the return side of the solar will fix it. What I think is happening is with the solar off it's going through your bypass tee fitting but still filling up your return line on the solar because of either not having a check valve on the return line or a busted one. And the head pressure gets to a point where the water just starts to fall, causing the knock.

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    Re: Repeated hammer/knock of solar when pump starts

    Quote Originally Posted by Solarseth View Post
    I've seen similar issues before and usually a new check valve on the return side of the solar will fix it. What I think is happening is with the solar off it's going through your bypass tee fitting but still filling up your return line on the solar because of either not having a check valve on the return line or a busted one. And the head pressure gets to a point where the water just starts to fall, causing the knock.
    That's what I suspect as well. There's a check valve there, but it didn't look great. Installed the 2/2.5 Jandy check valve as a replacement for the white PVC generic flapper check valve just now - waiting for the glue to dry so I can test it.

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    Re: Repeated hammer/knock of solar when pump starts

    Quote Originally Posted by matthewk4 View Post
    That's what I suspect as well. There's a check valve there, but it didn't look great. Installed the 2/2.5 Jandy check valve as a replacement for the white PVC generic flapper check valve just now - waiting for the glue to dry so I can test it.
    Replacing the check valve on the return line seems to have solved the problem. Check valve didn't appear to be in particularly bad shape when I pulled it out, but it must have been the cause.

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    Re: Repeated hammer/knock of solar when pump starts

    BooYaH! good deal.

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