Check Valves sticking

[Juice75]

My check valves are driving me nuts. They're the swing type, mounted vertically, and they keep sticking every time I go to fill my ballast for the first time.

Does anybody have any ideas on how to fix this? I've checked the valves, and there isn't anything in there. Will putting some grease or Vaseline inside the valves work?

Here's the type I'm using. http://www.plumbingsupply.com/pvccheck.html

Thanks