How to tell which pipe is pool?

[alosito]

The previous owner of our house had a spa which he removed and covered its place with concrete. Attached is how piping looks like, and my guess is one of the highlighted pipes was for the spa (or can they both be for my pool?). I am trying to find space to install an SWCG (Universal 40). So I though that if I could figiure out which of the highlighted pipes is for my pool, I can cut UL40 into it. As you can see on the picture, one of pipes has a valve. I am not sure what it was for, but it appears to be broken as no matter how much I twist it, it doesn't close. Are these valves usually installed on spa pipes? Can it be a solid indicator it is a spa pipe and the other one if for pool? Is there any other way to tell for sure which one if which?

 

[ajw22]

There is no way to guess what those two pipes lead to.

There is usually a 3 way diverter valve to switch water from the POOL return to the SPA return. So without a diverter valve I doubt one of the pipes went to the spa.

I would put the SWG in between the filter and the T leading to the two pipes.

You can disconnect the unions at the filter and move the filter a bit and blow shopvac air into the return pipe and look at where you see bubbles coming out to identify the pipes.