Ballast check valve

What do you think would be the best check valve to use in the front for this set up? I want it to have very little restrictions but not let any air back in when I drain the sac. I already talked to Flow-Rite and they said there check valves aren't made for that sinse it will have a vacum on it when I drain the front sac.

I had one of the brass gate check valves on my system before and it worked pretty good for a drain system. I mounted it so that it had to lift to let water out and lowered when the pressure was taken away. Helped it seal easier I think. I looked at the spring loaded, but figured it took pressure to open them and wasn't sure if they would open before the sac popped. You can get them in various sizes at Lowes.

Not letting air back in may be more tricky then letting water flow backwards through it. Check valves usually work with pressure forcing it shut. If there is no pressure to shut it, it will flap open once in a while and let air in. The sure fire way is to put a manual or automatic valve there so you know it is getting a positive seal.

Eric

We use the 3/4 " whale check valve, you can get them from boatersworld.com They let water out with out building pressure for the overflow and close off when the bag is being drained.