Last year, while trying to air lock my main drain I think I damaged my existing ball valve. I would blow air into the main drain line and could see bubbles coming from the main drain. I closed the valve and when I opened it to see if the air lock held, water was on the other side. It didn't come rushing up, it was already there. It sounds to me like the valve isn't air tight. I worked and worked on it last year before giving up and just pouring a bunch of anti-freeze in the line and hoping for the best. Fortunately, it worked as I had no problems this spring.
Fast forward to now and I am mentally preparing to close the pool soon. I saw that I have enough pipe that I can cut out the existing valve and put in a new one. My question is, which one? Praher? Jandy? Hayward? I want a quality valve that I won't have to replace (or can fix while it's installed). Does anyone have any experience with any of these and can offer a recommendation? Since I'll likely buy on-line I wanted to get some info before I ordered. I'd like one that is a union as well. I don't mind paying for a good product assuming it's proportional in quality.