What Kind Of Check Valve Should I Use?

[TomKattt]

I have an in ground pool and spa. The Spa is at a higher level than the pool so the water level is a foot or so higher than the pool's water level. I would like to set my water return to a mid point between the spa and pool to provide for better water flow into the spa during the day. But at night when the pump is off, water siphons back from the spa to the pool until the water level equalizes. Right now this isn't a problem if I keep the return valve set to the pool since it seals the Spa's return line. But, as I said, I would like to be able to set the return valve somewhere in between to insure there is fresh water flow into the spa.

I have a Jandy valve at the top of the return lines that controls the return into the two return lines. The return lines are vertical down flow. I would like to put a check valve into the Spa's return line but I do not know what kind of check valve to use. The Jandy check valve won't work in that configuration and I think that is true of all of the swing check valves. I don't know if a spring check valve will work, or what the requirements are for one to work in this application.

Any advice would be appreciated. Thanks.