Jamie, I had exactly the same problem with my acetylene tank. Mine is
a B Tank. I have a prestolite torch, only one gauge. No matter how
tight I tightened the key at the top of the tank, the pressure would
slowly creepup and by morning the gauge would register "full.
Pressure–in the red. There was no odor of gas, but just to be safe
I checked for leaks and found none. However, being a cautious person,
I called the company which supplies my tanks, and they said it was a
problem with the tank, and they immediately came out and replaced
the one I had with another one. According to what I understand, there
is a ring inside the tank that acts as a seal. If it is not seated
correctly, or is worn, the gas will seep out, causing the pressure
in the gauge to rise. At least that is what I was told
My advice is to call the company that refills your tank (or brings a
new one in exchange for the empty one), and get a new tank.