I have had a valve "stick" before...It was due to moisture in the airline and valve. If you have moisture in the valve and the temps get low then you can have that happen.
Make sure you have an Air/Water seperator, it helps but may not get ALL of it. You will also want to drain your air tank(s) every now and then...
black jacks, from fbi i'm thinkin. not to hard, just take em apart, remember how you did it, lube them up and put them back together, I had one i had to do a month or so ago.