I do not understand how my spa return works

[pmuvb]

The red arrow shows the pool return. The green arrows show two pipes that go into the spa return, so why there are
two of them?

And, what is the thing that circled in purple, is it a check valve for spa? It does not work, the water in the spa lowers once I turn off the pump.

 

[ajw22]

The check valve is not positioned for prevent your spa from draining when the pump is off.

The second line looping from the pool return though the check valve is to allow you to run your spa spillover and your pool.

The way your valves are there is no reason for that loop. I don't think the plumber was thinking clearly. You can achieve the same thing by the position of the first valve out of the pump. Right now you have both water paths to your spa open between the two valves.

You aware that running your spa spillover continuously causes aeration that raises your pH?

Aeration - Further Reading

www.troublefreepool.com

With your valves you can set three modes:

1. All return water to the pool
2. All return water to the spa
3. Return water to the pool and spa for spillover

 

[pmuvb]

I updated attached picture with numbering.

1. All return water to the pool - if i close both spa returns.
2. All return water to the spa - if I close return to pool. then there will be spillover.
3. Return water to the pool and spa for spillover - this is how it is right now.

What if I use valve 2 to close return to spa from pipe 1, let return to pool, and let retun to spa throught pipe 2, then should this set up prevent the water in the spa from draining?

Do I ever need to return to spa through pipe 1?

 

[ajw22]

After further study I think I see what the plumber did. I relabeled your valve positions below.

The problem he solved was not having the space to put a check valve in the spa return line to prevent the spa draining while having the spillover active.

If you put the first valve so position 1 is off. Now water flows from to the ABC T and can go to the pool or spa or both through the ABC valve. The check valve, if it is working properly, will now keep the spa from backflowing to the pool when the pump is off.

You can control the amount of water flowing through the spillover by the position of the ABC valve. Move the valve more towards A to reduce the spillover flow until you shut it off entirely at A.

Really no reason to use the 12 valve. The ABC valve can set any combination of pool or spa return water flow you desire. At A all water goes to pool, at C all water goes to spa.

 

[pmuvb]

I see, thx. I was confused about the two returns into spa, I'll prob just keep fist valve in position one, always. Looks like they did not see the design through from the start, it's not like there is a lack of space. I drained my spa at the moment but I'll test the check valve once I put spa to use.