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Thread: Check valve pulsing

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    Check valve pulsing

    Hello,

    The attached picture shows new plumbing for a recently-replastered pool/spa combination. I plumbed it in accordance with the Jandy standard plumbing diagram. All new parts. Previously the pool and spa were on completely separate circuits with dedicated pumps and no spillway or intermixing of water. During the replastering job we created a spillway in the spa dam wall so I could eliminate a pump and simplify the chemical balancing, so this is my first time with this new combo configuration.

    The current valve positions show normal operation: suction from the pool, return to the pool, and the spa make-up valve open to allow some return water to go to the spa and spill over the spillway into the pool. It works fine when running.

    However, sometime after the pump shuts off the check valve in the spa make-up line starts pulsing. You can see it and hear it. It's moving about 1/8 inch about 120 times per minute. This will cause the spa to drain down about an inch overnight, but not any more than that. The spa water level is still well above the pool water level in the morning, and the check valve is no longer pulsing.

    I can stop the pulsing by closing the spa make-up valve, but it will start up again when the make-up valve is reopened.

    Does anyone have any ideas what could be causing this? I could see the spa draining if the check valve were stuck open, but that doesn't appear to be the case here. How can a spring-loaded check valve pulse unless water was pushing it open from the normal flow direction, and if that were the case why isn't the spa filling instead of draining? There are no air leaks in the system, and everything else works fine.

    Thanks..valves.jpg

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    mas985's Avatar
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    Re: Check valve pulsing

    I have a couple questions:

    1) How high is the equipment relative to the pool level?

    2) What is the height of the spa relative to the pool level?

    3) Do you have solar?

    The symptoms suggest that there is water pressure against both sides of the check valve and I am just trying to figure out where it might be coming from. It may not be filling the spa because it is alternating in flow, thus the pulsing. You might try removing the check valve and see if the spring is working properly.
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    I have a couple questions:

    1) How high is the equipment relative to the pool level?

    2) What is the height of the spa relative to the pool level?

    3) Do you have solar?

    The symptoms suggest that there is water pressure against both sides of the check valve and I am just trying to figure out where it might be coming from. It may not be filling the spa because it is alternating in flow, thus the pulsing. You might try removing the check valve and see if the spring is working properly.
    1) The valve in question is 28" above the pool water level. I attached another picture of the equipment from a different angle. The deck slopes down to the left and away from the camera position in this photo. The bottom of the pump is about 3" above pool water level (the pool water level is 6" below the deck at the pool edge, but the deck slops down away from the pool). The only place in the entire system where water is higher than that valve is the top of the filter.

    2) The spa water is 9" higher than the pool water -- which would make the valve 19" above the spa water level.

    3) No solar. This is all of the plumbing. Except -- the air intake for the venturi jets in the spa is located over by the spa (as opposed to near the rest of the equipment) and it is 5 feet above the spa water level. Opening or closing the ball valve on this air intake makes no difference to the pulsing check valve.

    I had all the valves disassembled when I glued up the plumbing and the spring worked properly at that time. I haven't taken it apart again since then, but I can do that if you think it will help.

    I can also attempt to take a few pictures with a wider field of view -- showing the pool and spa in relation to the equipment -- if that helps.

    Thanks!

    equip.jpg

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    mas985's Avatar
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    Re: Check valve pulsing

    I think it would be worth inspecting the check valve spring just to make sure. The spa is raised so should have positive pressure against the check valve and close it and the spring should help. But there seems to be enough back pressure to open it back up which is unusual. The only thing I can think of is that a small air leak in the filter is allowing water to flow out toward the check valve. Do you find any air build up in the filter after it has been off for a while? Also, when the pump is first shut off, do you hear any air leak near the filter?
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    I think it would be worth inspecting the check valve spring just to make sure. The spa is raised so should have positive pressure against the check valve and close it and the spring should help. But there seems to be enough back pressure to open it back up which is unusual. The only thing I can think of is that a small air leak in the filter is allowing water to flow out toward the check valve. Do you find any air build up in the filter after it has been off for a while? Also, when the pump is first shut off, do you hear any air leak near the filter?
    No air build up in the filter, no air leak noise after pump shut off, no air bubbles in the volute.

    Interestingly, though, I just tried something. When the system is off and I crack the purge valve on the top of the filter to let a little air in on purpose, the check valve stops pulsing. As soon as I close the valve at the top of the filter the pulsing starts up again. That behavior is backwards from what I would expect and what you suggested about a possible air leak. Hmm.

    Also another data point.. Opening the regular return valve to the spa will stop the check valve from pulsing too. I assume that's because there's less resistance for the water to flow that way than through the make-up and check valves. Would it tell us anything if I configured it so the suction was from the pool and the return was to the spa and left it that way overnight? In that case the spa should drain down to pool level, correct? But if it doesn't that would support the theory that water is moving the other way and thus causing the pulsing.

    I'll disassemble and inspect the check valve tomorrow.

    Does the fact that the valves are so high above the deck have anything to do with this? Specifically with respect to the spa trying to push water to the pool through a valve that is higher than both of them? Due to the screwy layout of the pipes in the concrete I couldn't really plumb this any other way without using a bunch more 90s.

    Thanks.

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    Re: Check valve pulsing

    Quote Originally Posted by novca View Post
    No air build up in the filter, no air leak noise after pump shut off, no air bubbles in the volute.

    Interestingly, though, I just tried something. When the system is off and I crack the purge valve on the top of the filter to let a little air in on purpose, the check valve stops pulsing. As soon as I close the valve at the top of the filter the pulsing starts up again. That behavior is backwards from what I would expect and what you suggested about a possible air leak. Hmm.

    Also another data point.. Opening the regular return valve to the spa will stop the check valve from pulsing too. I assume that's because there's less resistance for the water to flow that way than through the make-up and check valves. Would it tell us anything if I configured it so the suction was from the pool and the return was to the spa and left it that way overnight? In that case the spa should drain down to pool level, correct? But if it doesn't that would support the theory that water is moving the other way and thus causing the pulsing.

    I'll disassemble and inspect the check valve tomorrow.

    Does the fact that the valves are so high above the deck have anything to do with this? Specifically with respect to the spa trying to push water to the pool through a valve that is higher than both of them? Due to the screwy layout of the pipes in the concrete I couldn't really plumb this any other way without using a bunch more 90s.

    Thanks.
    Here's an update. I disassembled and inspected the check valve. The spring works fine. It's actually very strong -- when the spa make-up valve is full open, the check valve flapper open opens about 30 degrees.

    I did another test to see how far the spa would drain down before the check valve stopped pulsing. Using a laser level I determined that the spa water drains down to a level equal to the elevation of where the pipes come out of the concrete at the equipment pad and then stops. It's still well above the pool water level at this point.

    I'm trying to wrap my head around this and can't come up with anything. Do you have any more ideas?

    Thanks.

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    mas985's Avatar
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    Re: Check valve pulsing

    When the system is off and I crack the purge valve on the top of the filter to let a little air in on purpose, the check valve stops pulsing.
    Does the check valve stay open or does it completely close when you do this?


    Would it tell us anything if I configured it so the suction was from the pool and the return was to the spa and left it that way overnight? In that case the spa should drain down to pool level, correct?
    The spa should drain down to pool level fairly quickly because there is nothing stopping it.


    One more thing to check. When the pump shuts off, does the filter pressure go to zero immediately or do you see the needle bobbing any?
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    Does the check valve stay open or does it completely close when you do this?


    The spa should drain down to pool level fairly quickly because there is nothing stopping it.


    One more thing to check. When the pump shuts off, does the filter pressure go to zero immediately or do you see the needle bobbing any?
    The check valve completely closes when I crack the purge valve on the filter.

    When the pump shuts off the filter pressure goes to zero immediately.

    And, of course, today after the pump shut off the check valve pulsing didn't happen at all -- it worked exactly like it is supposed to. The only thing I did prior to this change was disassemble and reassemble the check valve earlier in the day. Since I didn't find anything wrong with the valve, I'm not sure how this could have fixed it -- but maybe it did. I'll report back if the problem recurs.

    Thanks again!

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    mas985's Avatar
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    Re: Check valve pulsing

    There might have been something stuck in the hing.
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    There might have been something stuck in the hing.
    It worked fine for two days but now it's back to pulsing. The spa drains down overnight to a level that matches the elevation of where the pipes come out of the ground at the pad and then stops -- still well above the pool water level. Very strange.

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    mas985's Avatar
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    Re: Check valve pulsing

    Just to confirm, when you first turn on the pump, do you see any air coming out of the returns?

    The only way that it would stop above pool level is if it reaches a break in the siphon normally caused by an air pocket.
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    Just to confirm, when you first turn on the pump, do you see any air coming out of the returns?

    The only way that it would stop above pool level is if it reaches a break in the siphon normally caused by an air pocket.
    Nope -- no air anywhere. Not in the returns, the volute, or the filter.

    Closing the spa make-up valve will stop the check valve pulsing -- but then re-opening the make-up valve will allow the pulsing to start up again almost immediately.

    Moving the main return valve from pool to spa will stop the check valve pulsing. Moving the main return valve back to pool will cause the pulsing to come back eventually, but not immediately like described above.

    Allowing a bit of air into the top of the filter will stop the pulsing for a bit, but then it starts up again.

    It's not the end of the world and I can live with it -- but it bugs me. From a hydrodynamic standpoint it shouldn't be happening...

    Thanks.

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    Re: Check valve pulsing

    Are you sure the suction side valve has the SPA completely off and is working properly? That could also explain the behavior.
    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: Check valve pulsing

    Quote Originally Posted by mas985 View Post
    Are you sure the suction side valve has the SPA completely off and is working properly? That could also explain the behavior.
    I installed all the valves and pad plumbing brand new six weeks ago. The valves were disassembled while gluing and inspected afterwards, so I know none of the PVC cement got into one of them.

    With the pump running I know the suction side valve works properly because there is no transfer of spa water into the pool when it's isolated and the make-up valve is closed -- so my assumption is that it's working properly when the pump is turned off as well.

    I can also hear the water in the pipes and the pump noise change when I actuate the suction valve with the pump running, so I can tell when it's fully closed to one side or the other. I've transferred water between the spa and pool numerous times by manipulating these valves with no problems.

    The check valve pulsing also occurred before I plumbed the heater into the circuit (I left the heater out of it for the initial plaster curing process), so the heater plumbing shouldn't be a contributing factor.

    Intermittent problems that don't make sense are the hardest kind to troubleshoot...

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