Solar system - correct routing of return line 3 way valve

[Laker4ever]

Hello everybody,
I'm in the process to remodel my pool that include re-plastering, new tiles, and new plumbing.
Since my system has solar panels, i would like to get your comments on my existing setup. I have some doubts about it and its correctness.
My solar uses FAFCO 11 panels (Because of the roof structure, i got one section of 4 and another of 7) that are all plumbed with 2" black pipe on the roof and white on the remaining portion (PVC or ABS not sure) . I have a G35 Goldline controller that has a switch and thermostat dial to adjust temperature. My current setup has the pipe that is coming from the filter has a Tee, and one split goes to the roof (cold) for the panels. The other end of the Tee, goes to a 3 way motorized Jandy valve. That valve selects between this line and the output (hot) from the solar. The output of that valve runs to my gas heater, and from the heater to a SWG (Pentair IC-40), then it goes to the pool return lines. There are no check valves in those lines, expect at the output of the DE filter.
My question is that I have seen many diagrams with solar, and all are calling for the 3 way valve to be placed as the selector between where to divert the cold water into the solar or bypass to the pool, and have a Tee on the solar output with a check valve.
In my setup (the opposite), it seems that on any pump startup, it would require the pump to fill the line of solar panels even if the solar is switched off by the goldline controller. It seems that it will always be under pressure.
Now that I remodel it, Should I change that to be like all of the diagrams are calling for?
What are the benefits? and is it critical?
Thanks much!

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40' x 20' gunite pool Pentair SMBW4060, ultra flow 1.5HP 1.47SF, IC-40 SWG, 11 FAFCO solar.

 

[mas985]

My question is that I have seen many diagrams with solar, and all are calling for the 3 way valve to be placed as the selector between where to divert the cold water into the solar or bypass to the pool, and have a Tee on the solar output with a check valve.

This is the way I normally see it too.

In my setup (the opposite), it seems that on any pump startup, it would require the pump to fill the line of solar panels even if the solar is switched off by the goldline controller. It seems that it will always be under pressure.

True which is why it is usually done the other way.

Now that I remodel it, Should I change that to be like all of the diagrams are calling for?
What are the benefits? and is it critical?

The panels will only fill to the level of the vacuum release valve or slightly past it. Where is your vacuum release valve located? But in the rest of the panels and/or lines, there will be compressed air which will tend to rush out with the water when the pump is shut off. Air is much more compressible than water.

Also, do you have a check valve after the filter and before the tee? Otherwise, when the panels drain, they could drain backwards through the filter.

 

[Laker4ever]

Only benefit i see is that if panels are not used, at least they will be full of water and maybe if it is really hot, they will not get damaged by the excessive heat as the water in them, while not moving, still provides cooling to the panels (tubes) themselves.
Since i have two sets of panels, they actually put the pressure relief valve on the top of the 1st set. But the 2nd set is actually higher... I was considering to install another pressure relief valve on top of the 2ns set too. Will that work?
I have only 1 check valve after the DE filter output. But i also suspect that it is not too good, as if for ex, i turn off the pump (kill the power), and the 3 way valve is in the solar position, it does drain (not all the panels, but some) and i can see DE pushed in the skimmer....and into the pool.
So i installed recently another new check valve at the pump output and that stopped the problem.

 

[mas985]

I think that the panels and pipes are more likely to get hotter if there is water in them than without. Water is a great heat sink and will store large amounts of heat. I'm not sure where you are located but bepending on the type of pipe you have on the roof (ABS or PVC) and how hot the sun gets, there is a small chance that one of the pipes could collapse or deform under the intense heat when the water drains from them and creates a vacuum.

Having two vacuum release valves should work ok but it depends on if you have an local low spots between the panels, they may not drain. My prefrence is always to have one valve at the highest location. Suction caused by the water draining on both sides will ensure all of the water is cleared out. But with the solar valve where it is, you may never be able to drain the return side unless the valve is on. If you are planning on replumbing the pad soon, you might consider moving the control valve.

Also, if you have a check valve on the output of the filter, that should have stopped the backflow of DE into the skimmer. A check valve before the filter or after should have the same effect although having one before the filter may encounter some debris that would keep it open some so my preference would be after the filter. So it could be that the check valve after the filter has gone bad.