The fuel cap on man classic camping stoves (Kerosene stoves such as the Primus 210, Primus 96, Optimus 45) made in Sweden or elsewhere in Europe are basically the same. A screw cap with a outside diameter from 23 mm, inside diameter 18 mm and a pinhole screw that can be opened to release air pressure out of the tank. In order to keep the stove working it is important that the pressure is maintained inside the tank. This is ensured by adding a extra rubber ring inside the fuel cap. Over the years and decades this rubber ring will become stiff and brittle. Although mostly not visible the rubber then doesn’t seal the fuel cap air tight. The result is that once the stove is burning the flame will fade away due to leaking pressure. Then it is time to replace the seal for a fresh and flexible new one.
Material of choice
It is from uttermost importance that the seals are made from the right material with the characteristics suitable for the purpose. In the case of liquid fuel stoves the material has to be able to withstand fuel (solvents, aromatic compounds, organic solvents etc.) in the first place. Resistance to heat and flexibility is also important. Many rubber types such as NBR or EPDM are affected by fuel. The rubber can swell up or can completely disintegrate into rumble. This isn’t immediately visible but will happen over time. Usually after a few weeks or months the problems will occur. To avoid this a high performance rubber such as Viton® (a trademark from DuPont for FKM) is a good choice.