Sticking check value in a tavern head?

Does a tavern head on a commercial keg have a valve of some type in it that can stick? I have a keg setup for Smithwick's that on a fairly consistent basis does not flow beer when the faucet is pulled. I have disassembled and cleaned the faucet, verified CO2 pressure (5 pounds typically) is on, disconnected the tavern head from the keg and reattached, etc. The beer does end up flowing after opening and closing the faucet multiple times (sometimes a bunch!). I've also lightly tapped the side of the tavern head with a wrench, sloshed the keg slightly and other things to somehow stimulate the beer flow.

Any thoughts on what's wrong?

Thanks...