Petromax 829 Manometer Disassembly

Hello, I finally got my first Petromax and it’s a nice very lightly used German 829 made in 1966 that I’m doing a complete rebuild on including having the fount, burner cage & vent nickel plated as it spent its life near the coast and that salt air did a number on its finish. I’m trying to take the manometer apart so I can restore the plastic crystal and have the casing re-plated but I can’t figure out how to remove the air valve screw so I can slide the cover off. Beneath the air hole there is a hole and that’s where I figured the retaining screw or pin would be but all I see is a somewhat smooth surface without a screwdriver slot. Was this the head of a screw originally? Is this what keeps the vent screw captured, what am I missing on getting this disassembled? Thanks!

 

The thread of the vent screw is crimped together in the upper part to prevent the loss of the screw. You can remove it by just turning it further, but there is a risk that the shaft will snap off.
The open hole is the bleeding hole, and the solder filled in the lower hole is making the seal against the screw. There's only one small screw which holds the manometer's cap in place. I'd recommend not to re-plate the lower part of the manometer because it is hard to disassemble and you also might damage the burden tube.

 

Thanks for the reply Martin, good advise on plating only the top cap but I am unable to remove it because the head of the vent stem is in the way, it’s attached to the lower half of the case on my manometer. I have backed it out as far as it will go without forcing it, something is apparently capturing it to keep it from backing out all the way.

 

you'd need to force the screw out.
No way to remove the cap with the screw in position.

Erik

 

I imagine there is a good risk of bending or breaking the stem if forced and once removed it will no longer have a positive stop and will back out all the way if you keep twisting it? Sounds like it would be best if left alone, the nickel plating is not that bad on this piece just really thin and I can do a decent job pf polishing the scratched plastic dial face while it’s still in the manometer. Thanks.