Thanks Watermom for the welcome! I went ahead and installed the chlorinator without optional check valve. The PVC pipe was not that long, but I think I left enough room for the Pentair check valve just in case. From reading, it looks like it is a 1.5" valve that fits inside 2" pipe... this may restrict water flow a little. Since I don't have a heater, I think I may be OK as is. My only concern is on the flow to pool side of the 320, the PVC connects to metal pipe that feeds the water to the pool.

And thanks for this forum! I've learned a lot just from reading posts.
Bob