On my system, the check valve is between the filter and the 3 way. This prevents back flow through the filter (really bad…) when the solar shuts off and the panels drain. I’m still not sure what the purpose of a check valve on the solar return is. I’ve only seen diagrams with the check valve between the filter and 3 way valve.
Undersized Pool Solar...Is it worth it?
- Thread starter joeprunc
- Start date
Prevents panels from filling while the system is off while allowing for draining.
Ok, I sort of understand, but since the 3 way is closed, back pressure will do that for the most part. You certainly won’t get flow through the panels. It won’t hurt. But, a check valve on the filter side should be used to prevent back flow through the filter if the pump shuts off when the panels are full.
You're forgetting the open vacuum relief valve at the top of the array. It will allow water to back fill the panels until they are full and it is forced closed.
Not trying to argue, but that absolutely does not happen on my system. I know for a fact that little if no water goes through the solar return when the pump is running but the solar is off. Also, the vacuum breaker doesn’t open under pressure, it opens under vacuum (in order to let the panels drain when the solar shuts off). If the vacuum breaker opened under pressure, all of the water pumped up to the panels would flow out onto the roof.
I don’t see any problem with a return check valve, but don’t think it’s critical. A check valve between the pump/filter and the 3 way is critical to prevent backwashing into the pool when the pump shuts off if the solar is running.
Installed solar for 12 years before a severe injury stopped that. Went to every school that was available at the time. Only recommending what was taught as best installation practice and how it was done by me. The thinking was to anticipate the issues that may arise and eliminate them before they do. Makes for happy customers. A second check valve was automatic. One to stop reverse flow through the filter, one to stop reverse flow through the panels.
Just my opinion. Your pool, your money, your choice.
A true solar vacuum relief valve is a normaly-open valve that closes under water pressure, but will allow some air to purge as the panels fill. Some aren't even on the array, but on the supply line near the equipment. Since every pool installation is unique, your experience may be different.
Just my opinion. Your pool, your money, your choice.
A true solar vacuum relief valve is a normaly-open valve that closes under water pressure, but will allow some air to purge as the panels fill. Some aren't even on the array, but on the supply line near the equipment. Since every pool installation is unique, your experience may be different.
- May 3, 2007
- 16,878
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
A typical VRV remains open until water pressure closes it. They are designed to stay open with air pressure but not water pressure so for it to close, water must reach it.
But even IF the VRV closes immediately after the pump starts, air is compressible so the water will travel up into the return pipe until the pressure is equalized and the air is under significant compression (i.e. gas law). The atmosphere is at 14.7 PSIa and if the internal plumbing is at a 20 PSIr (34.7 PSIa), then the air will be compressed by close to 60% so water will fill at least that much of the solar plumbing.
How do you know for sure this does not happen on your system?
But even IF the VRV closes immediately after the pump starts, air is compressible so the water will travel up into the return pipe until the pressure is equalized and the air is under significant compression (i.e. gas law). The atmosphere is at 14.7 PSIa and if the internal plumbing is at a 20 PSIr (34.7 PSIa), then the air will be compressed by close to 60% so water will fill at least that much of the solar plumbing.
How do you know for sure this does not happen on your system?
So, not as sure as I made it sound
, but haven’t ever noticed the normal effects that happen when the solar kicks in - water sounds on roof, bubbles from returns, heat gain etc. My 3-way valve is “leaky” anyway ( has a small hole drilled in it to allow water to drain off the panels from the pump side). This was the standard installation when my system went in 15 years ago. So even with a check valve on the return, it is likely that some water is flowing into/through the panels when the solar is off. Is this still the standard? My main point really isn’t the return check valve, I don’t think it’s necessary and certainly not required for a working solar system but doesn’t hurt so why not. My main point really is that the diagram is missing the critical check valve to prevent backflow through the filter if the pump shuts off when there is still water in the panels. Do we all agree to that? And, I was wrong, it does show that check valve
. Sorry about that, guess I was too relaxed sitting by my nice, warm solar heated pool!
Last edited:
- May 3, 2007
- 16,878
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
Check valves can and do leak. Also, if you have a solar valve with a built in drain hole or check valve, that too can leak. So everything needs to be in perfect condition to prevent the panels from filling when the solar valve is off. Also, if the valve turns off while the pump is running, unless the RPM drops, the panels will not drain anyway.
- Apr 26, 2021
- 83
- Pool Size
- 20000
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Wow...a lot of great discussions and being an engineer, I appreciate all these items listed below.
I was able to get two arrays up on the limited roof space I have this weekend. Happy with how clean it turned out, and think summer time will provide enough heat to keep my wife happy (in the spring/fall I'll keep the solar cover on to help) The photo below is at 6:30 PM.
Still two lingering questions around my specific layout:
Check Valve Question: I will be installing one check valve on the solar array return. I want to put a check valve between my filter and solar 3 way valve, but I do not have space without major equipment or piping modifications...which option do the professionals see as a better forward path?
1) Install a check valve between the filter pump and filter?
2) Do the math on solar draining. I have the arrays sloped towards the lower inlet header, therefore when the pump is off the only draining would be through the solar return (approx. 15' head and approx. 25 ft of piping). The closest pool suction piping to skimmer is approx. 30-35 feet. My thoughts are to have the filter pump run at minimum RPMs...say 800 RPM for 30 minutes to allow the return to drain and be pushed towards the pool return.
Vacuum Valve Location: My pool solar instructions call out to install the vacuum relief vent on the inlet side of the array, where my engineering basics tell me to put the vacuum vent at the highest point. I can do either or, but the one on the inlet side will be significantly easier location to change in the future if it were to fail.
I was able to get two arrays up on the limited roof space I have this weekend. Happy with how clean it turned out, and think summer time will provide enough heat to keep my wife happy (in the spring/fall I'll keep the solar cover on to help) The photo below is at 6:30 PM.
Still two lingering questions around my specific layout:
Check Valve Question: I will be installing one check valve on the solar array return. I want to put a check valve between my filter and solar 3 way valve, but I do not have space without major equipment or piping modifications...which option do the professionals see as a better forward path?
1) Install a check valve between the filter pump and filter?
2) Do the math on solar draining. I have the arrays sloped towards the lower inlet header, therefore when the pump is off the only draining would be through the solar return (approx. 15' head and approx. 25 ft of piping). The closest pool suction piping to skimmer is approx. 30-35 feet. My thoughts are to have the filter pump run at minimum RPMs...say 800 RPM for 30 minutes to allow the return to drain and be pushed towards the pool return.
Vacuum Valve Location: My pool solar instructions call out to install the vacuum relief vent on the inlet side of the array, where my engineering basics tell me to put the vacuum vent at the highest point. I can do either or, but the one on the inlet side will be significantly easier location to change in the future if it were to fail.
- May 3, 2007
- 16,878
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
I see the check valve between the filter and the solar valve as mandatory. If you turn off the pump, some of the water will flow backwards through the filter. It is a given. The return check valve is optional but also highly recommended.
As for VRV location, the closer to the pump you plumb the VRV, the lower the RPM is needed to keep the VRV closed. Some people plumb the VRV about 6' above the pump on the supply side of the panels so they can run their pumps at the lowest RPM possible and save the most amount of energy costs. The downside of this is that the panels will only drain when the pump shuts off but you can work around that with proper run time management (i.e. only run when solar is available).
The check valve in the solar supply is to keep the water from flowing backward through the filter and "backwashing" it into the pool through the suction line (and possibly damaging cartridges). If there is no room after the filter, before is good for that purpose. If no room there, in front to the pump will accomplish the same goal. You just learn to service your system accordingly.
Some VRV have been at the top of the array in the same panel that the feed enters, some at a point 5 or 6 feet up the supply line, depends on manufacturer's suggestion. I serviced pools for about 20 of the years I have done the work, still service equipment, and have seen most all installation variables (including the ones I did). They all worked well. Just variations of the same theme; get the water through the panels, let it drain when not in use, make sure the flow is only one way.
Some VRV have been at the top of the array in the same panel that the feed enters, some at a point 5 or 6 feet up the supply line, depends on manufacturer's suggestion. I serviced pools for about 20 of the years I have done the work, still service equipment, and have seen most all installation variables (including the ones I did). They all worked well. Just variations of the same theme; get the water through the panels, let it drain when not in use, make sure the flow is only one way.
- Apr 26, 2021
- 83
- Pool Size
- 20000
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Thank you all,
I think the info above provides enough guidance.
I'll plan on installing 2 check valves; one between filter pump and filter, and one on solar return line. @1poolman1 The one between the filter and pump makes sense that is should eliminate flow through the cartridge filters and force the arrays to drain to the pool return plumbing.
The VRV I'll install at the solar array inlet header approx 8' in elevation.
I think the info above provides enough guidance.
I'll plan on installing 2 check valves; one between filter pump and filter, and one on solar return line. @1poolman1 The one between the filter and pump makes sense that is should eliminate flow through the cartridge filters and force the arrays to drain to the pool return plumbing.
The VRV I'll install at the solar array inlet header approx 8' in elevation.
- May 3, 2007
- 16,878
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
I am not a huge fan of putting check valves before the filter because debris can interfere with the operation.