Sankey couplers leak when changing keg

[freshtube]

I have keg couplers that are leaking out the beer in the line when changing a keg..shouldn't they stay tight and full of beer when you unlock the mechanism and change the keg or leave it off? There's several kegs on the system and they all have the same problem. It seems like there isn't pressure to engage the ball and lock the beer in or something but there's 12psi on the regulators and beer is pouring fine when they're on? Or there's a seal thats shot inside the coupler, but on all of them? Any help much appreciated!

[IanCharles]

I'm having the same problem. Shouldn't our D Sankey couplers NOT leak air when disconnected from a keg?

[djc]

There is a check valve in the coupler just below the beer line to prevent back flow. There are a few types - primarily you will see torpedoes and balls. Your check valves are either missing or stuck.