Bringing THIS Petromax pattern EFAR 608 back into service it smelled of unburned fuel on initial test firing and occasional wisps of vapourised fuel were visible at the hood. Inspection revealed that the threads cut in the thin steel of the J-tube that mated with those on the brass screw operating the blade valve were badly corroded, to the extent that the screw was barely secured, hanging literally on a fraction of a thread. I removed the valve and silver soldered a stubby brass plug in place, considering that the option to fine tune the fuel/air mixture wasn’t too great a loss. The grade of solder I used, with only a 30% silver content, puts its melting point well above the temperature it will encounter in that location. The lamp was odourless and worked flawlessly subsequently. Although the ‘butterfly’ fixing doesn’t have to be gas-tight to the extent of withstanding the pressure encountered in the fuel tank in operation, a combination of the velocity of the vapourised fuel and air stream, turbulence in it passing the butterfly blade and residual gas pressure sought out the small gaps in the thread. I post this here rather than in the Fettling Forum to invite discusion on the phenomenon of ‘butterfly’ leakage coupled with a smelly lamp! John
An effective fix on the issue, @presscall . I have never had any serious leaks on the 'butterfly' paddle threads. The paddle is simply attached by means of the threads mentioned for many Petromax clones, and can be completely removed by unscrewing it off the J-tube. On the post-WWII genuine Petromax, these cannot be unscrewed off without deforming the retention piece that is attaching the limited-rotatable paddle in place. On the clones, I've encountered threads that had been corroded, worn or simply "over-loosened" due to to other reasons. They can be a source of leak if the thread engagement is inadequate, perhaps merely a turn or two. Mine hadn't been that serious to need permanent plugging. But I could recall using some copper anti-seize compound on the threads to reduce the likelihood of any serious leaks. Initially, upon firing up the lantern, the petroleum constituents within the copper-antiseize would start smoking off. Eventually, the petroleum base would be exhausted, leaving behind a mixture of graphite and copper powder filling the gaps in the paddle threads. While it might not be absolutely gas-tight, it does impede to a great extent, the escape of any umburnt fuel vapour through them. The paddle isn't permanently fixed in position and can still be rotated if needed. On many accounts by users, the paddle's function hadn't been particularly significant. They can even be omitted completely, like in newer designs. However, not all are such. I do have some units of Petromax and clones which required specific angles on their paddles' orientations for the optimum burn at the burner cap and hence the optimum intensity/brightness of the mantles. While many worked with the most common 90° or straight-vertical orientation of the paddle, some of mine worked better at 45° or other angles. There had been a coule of them which had best performance at 'horizontal' or zero degree paddle orientation. Other degrees of orientation could produce decent light too but just not the whitest, most intense glow of the mantle.
