These valves can get hot and may have a small flame erupt at the stem. The threaded cover that is around the turn stem covers a packing that seals
the stem from leaking fuel
. You may be able to compress the packing by turning the nut tighter. If not, your local hardware
store probably has the correct packing.
This is covered in Calder's Boatowner's Mechanical and Electrical
I find these pressurized alcohol stoves to be very good to cook on.