Pulled into our usually station to top off our Gaslows and had a problem. The van is new to us and the new R67 twin Gaslow cylinders were fitted by the seller. This was the first time I had filled them. Connected the pump as normal and added about 20 litres. Dropped the lever and went to disconnect but instead of the usual quick pressure release gas kept pouring out. At a guess a non-return valve had stuck open. Eventually something changed and the flow stopped, got the filler disconnected checked the gauges and both cylinders were showing full. Will not be able to try again for a while but wondered if this is a common problem.