Knocking/Hammer/Thumping noise from pipes when pool pump shuts off

[Cartman269]

Hello everyone, I have done a search and can't find anything specific to my situation, a few are close but a little different so I thought I would post my concern and see if anyone can help me solve it. My wife and I just had the roof replaced on our home a month or so ago and ever since the solar panels were reinstalled, we have had an intermittent thumping noise (like a bass drum) that occurs every 5 seconds or so and continues for about a minute after the pool pump shuts down and just before the solar panels start to drain.

I have been able to replicate it and isolate it to the solar panels draining by manually turning off the pool pump. If I turn off the supply and return lines from the solar panels as soon as I hear the thumping the noise will stop, when I then open the valves back up the noise begins again. Once the noise has occurred for 30 seconds to a minute it will stop and then I hear the solar panels drain. I have noted that the vacuum gauge on the pool filter will jump in time with the thump noise.

I think either the check valve just after the filter is faulty, or possibly the vacuum relief valve is bad for the solar panels, although the panels seem to drain ok (I does take about a minute before they begin to drain, not sure if this is normal as this is our first pool and I never paid all that much attention before). I do get the 30 second or so burst of bubbles when the solar panels are activated, and I have seen no bubbles during solar panel use other than initial start up.

I have posted pictures of my pool equipment set up and a link to a you tube video where I am able to replicate the noise, although the noise is generally louder than it seems on the video. Thank you for your help

 

[mas985]

What you are hearing is called water hammer and is most likely caused by a check valve on solar that is slamming shut when the water tries to drain downward. This should only happen when the solar valve is still engaged when the pump shuts off. You probably won't hear it when solar first shuts off, then the pump shuts off which is usually normal operation.

 

[Cartman269]

You are correct that we do not hear it as the solar turns itself on and off throughout the day. We only hear it when the pump shuts off for the night, at 7:30pm, and is loud enough to be heard throughout the house while watching TV, etc. At this point the solar panels have been closed for about two hours with the temperature dropping in the afternoon and early evening (the valve is automatic using a solar touch for control). I just went out and checked (currently 5:19pm) and the solar valve is shut, the pool pump will be turning off in a little over two hours from now. I have attached a picture of the current valve position.

Are you saying the hammering is normal when the pump shuts off for the evening? If so I am a bit perplexed as we have not heard this noise until very recently. Or are you saying that the check valve you point to is most likely faulty?

Thanks again

 

[mas985]

Unfortunately, that can happen with some solar installations. The problem is that when the pump shuts off, any water in the return pipe will flow down very quickly and run backwards towards the filter slamming the valve shut. Not too much you can do about that. The closed solar valve slows the back flow from the supply side so that probably is not an issue.

However, I noticed that there is no check valve on the solar return. Normally , installers will put one there. That helps to prevent the return pipe from filling when solar is off at pump start up. However, it probably won't help much when solar is on then turns off before the pump turns off. In that scenario, the return pipe remains filled with water because the pump pressure does not allow it to drain.

Is that a single speed pump?

How high are the panels relative to the pad equipment?

What is the filter pressure when solar is off?

With a VS pump and controller, when solar shuts off, you can command the pump to reduce speed. This allows the panels to drain some so the noise is not so bad when the pump shuts off.

 

[JamesW]

If the flapper does not have a spring, then it can open and close.

Change the check valve to a Jandy check valve with a spring.

 

[mas985]

It will still slam shut when closing.

 

[JamesW]

The problem is that the flapper is bouncing up and down causing a thumping noise.

That should not happen with a spring check valve.

 

[mas985]

True but it may slam shut instead. That is what happened with my system when it was on the roof.

 

[mas985]

Here is a crazy thought. If the VRV was more restrictive, it would drain slower. Then the spring loaded check valve may not close as fast.

But this is only a problem with non-VS pumps because VS pumps have slow start/stop which prevents the valve from slamming shut.

When I changed to a VS, the problem went away.

 

[Cartman269]

The filter pressure is at 18 psi when the solar panels are active with the pump running at 2,450 rpm. With the solar panels inactive the pressure is 8 psi with the pump running at 1,750 rpm. I have attached photos for reference.

I can check the height of the solar panels. They are installed on the roof of a single story home, so not too high. Would you need the maximum height, or the topmost portion of the solar panel or would the supply and return pipe height and length along the roof suffice.

The pump I have is the intellipro 2 VSP, so it is a variable speed pump. It is running at 1,750 rpm unless the solar panels are active in which case it runs at 2,450 rpm. Slowing down the pump may be a solution, but I am unsure how to do the calculations to make sure I am at the correct speeds. These speeds were set up by the solar panel installers.

I can not find a model number on the current check valve. I have included pictures for your reference if needed.

If the flapper does not have a spring, then it can open and close.

Change the check valve to a Jandy check valve with a spring.

Is there a Jandy model check valve you would recommend?

 

[JamesW]

https://www.ndspro.com/PDFs/Catalogs/NDS-Flow-Management-Catalog.pdf

https://www.ndspro.com/PDFs/Catalogs/NDS-FlowManagement-Catalog-2022.pdf

Check Valves - Valves - Flow Management - Shop

www.ndspro.com

 

[Cartman269]

Thank you for the catalogs, I am new to pool maintenance and repair so forgive me if my questions seem naive.

I think I should probably try replacing the check valve first, my thinking is it has probably just worn out over time, versus adjusting the pump speeds first.

I have the plans from our solar installer and it lists “HC-1790” next to the check valve. It appears that would be my model number to use for replacement, after choosing the right pipe diameter.

Would I be able to just unscrew the old check valve and install the new check valve (assuming the replacement valve is the same length) reusing the “union” portion of my piping, or should I cut the piping and glue in the unions which come with the new valve?

 

[1poolman1]

You are correct that we do not hear it as the solar turns itself on and off throughout the day. We only hear it when the pump shuts off for the night, at 7:30pm, and is loud enough to be heard throughout the house while watching TV, etc. At this point the solar panels have been closed for about two hours with the temperature dropping in the afternoon and early evening (the valve is automatic using a solar touch for control). I just went out and checked (currently 5:19pm) and the solar valve is shut, the pool pump will be turning off in a little over two hours from now. I have attached a picture of the current valve position. View attachment 548062

Are you saying the hammering is normal when the pump shuts off for the evening? If so I am a bit perplexed as we have not heard this noise until very recently. Or are you saying that the check valve you point to is most likely faulty?

Thanks again

There should be a check valve in the solar-return line coming from the roof, the one to the right past the valve, in the picture above. Even with the solar "off" water is going to the roof through the solar-return line when the pump is running. When it falls back it slams the existing check valve, that is there to prevent damage to the filter cartridge, closed and you get the hammer effect. There probably nothing wrong with the existing valve. Even if there is, you should install one in the solar-return line first. The ones with unions that JamesW recommended are easy to install in an existing line.

 

[Cartman269]

Thank you for that explanation, that makes a lot of sense. Perhaps I am overthinking things a little, but it seems to me that I would need to also adjust the “solar off” speed of my pump to allow the column of water in the return line to “fall” down further than what it currently does when the solar panels shut off. The check valve would keep the water from climbing back up the column, however it seems to me that if my pump output and pressure are too high it would prevent the solar panels from fully draining when they turn off

 

[Cartman269]

I am going to try replacing the current check valve first. I went out and took some measurements and it looks like I should be ordering the 1700-20. The check valve is for 2" diameter schedule 40 and is 6 1/8" in length. I see it is available with a 1/2 lb spring and a 2 lb spring, part numbers 1700-20 and 1702-20 respectively. Which spring strength should I order?

 

[JamesW]

1/2 lb.

 

[mas985]

Thank you for that explanation, that makes a lot of sense. Perhaps I am overthinking things a little, but it seems to me that I would need to also adjust the “solar off” speed of my pump to allow the column of water in the return line to “fall” down further than what it currently does when the solar panels shut off. The check valve would keep the water from climbing back up the column, however it seems to me that if my pump output and pressure are too high it would prevent the solar panels from fully draining when they turn off

This is correct. Do you have a controller that controls both the solar valve and the pump? If so, you should be able to set it up so that when solar is engaged, one speed is used while when solar is off another speed could be used.

For many setups, solar requires a higher speed for priming and keeping the VRV closed while a lower speed can be used for filtering and skimming when solar is not on.

 

[Cartman269]

This is correct. Do you have a controller that controls both the solar valve and the pump? If so, you should be able to set it up so that when solar is engaged, one speed is used while when solar is off another speed could be used.

For many setups, solar requires a higher speed for priming and keeping the VRV closed while a lower speed can be used for filtering and skimming when solar is not on.

Yes I do have a solar controller, it ramps up the speed on the pump to 2,450rpm and opens the automatic valve to allow the water to flow through the solar panels. When the solar panel temperature falls below a specified temperature difference with the pool water, or when the pool temperature reaches the set point the controller closes the valve to the solar panels and slows the pump down to 1,750 rpm.

Is there a calculator or equation I can use to see if my slower (non solar) speed is correct?

 

[Cartman269]

1/2 lb.

Thank you, I have ordered a new check valve. I will let everyone know how it works out

 

[mas985]

Is there a calculator or equation I can use to see if my slower (non solar) speed is correct?

A calculator is not necessary. There is no turnover requirement for a residential pool. There are only a couple of factors to consider depending on how you run your pool and the equipment you have.

1) SWG - RPM needs to be high enough to trip the flow switch. But that is usually pretty low RPM for most setups. I would try 1000 RPM and see if the SWG still works.

2) Skimming - Find the lowest RPM where water travels over the weir door instead of around the sides. This will have a higher surface velocity so that skimming is more effective.

3) Heating - For you this is probably not a factor at all since you have solar but some heaters require a certain flow rate or pressure to operate properly.

The idea here is run at as low an RPM as possible to keep energy use as low as possible. I suspect you can operate well below the current 1750 RPM without any impact.