Blown tank bottoms on X246B lamps

Having read on this forum some horror stories about bulging tank bottoms, could I ask you fine folk what the standard shape of the bottom should be? Should it be completely flat or is a slight bulge normal?

The rim on my lamp, that is the edge the lamp stands on, is 5mm below the tank bottom which is slightly bulged out. How say ye?

 

Photographs will help us to assist you.

 

In my opinion there X246B or any unsupported flat bottomed fount will have a slight bulge. Understanding that when the fount is pumped up to over 25psi, working pressure, there is a pressure force of over 2000lbs or 910kgs. Any flat plate surface will flex or bulge with this force.
The question is how much.
I would gauge it acceptable if the lamp sits on a flat surface without rocking on the bulge. As soon as there is evidence of the bulge causing the lamp to rock or when turning the lamp over and seeing scuff marks on the base caused by over bulging ...... I would deem it “blown” and condemn the afflicted fount.
Just my thoughts
Cheers
Pete

 

@R100

Your X246B measurements sound about right for a good X246B.

As Pete says, when the bottom plate hits the flat surface you know your in strife.

Cheers

Tony

 

Thanks for the very reassuring replies. I never realised how much there was to learn about such basic pieces of kit! Anyway, here are photographs as requested.

 

@R100 she’s good, in my opinion. Nice looking lamp.
Just don’t over pump the X246B. I usually use about 30 or so pumps on a full fuel load.
Cheers
Pete

 

Thanks Pete. Just what I was hoping to hear. I am very pleased with the cosmetic restoration as it was tired and neglected when I acquired it. i'm just waiting for a seal pack and mantles then its time to tango.

 

@R100 you’ve done an excellent job. Don’t forget to post the money shot (its first light).
Cheers
Pete

 

Thanks for the kind remarks. I will post first light shots in due course.

 

Stand it on a flat surface, if it wobbles, its f*****.
If its one you're going to refurbish, place it on a rough flat surface and move it about, if scratches appear on the floor of the tank.... see above

 

Thanks for the advice. I'm certainly relieved that this test is not applied to old geezers like me!

 

Of course it's the 'free space' above the fuel that compresses, so a full tank won't require as many pumps as one that is only a quarter full (the smaller volume of air compressing more easily) Once You've done it a few times you get to feel the slight resistance on the pump that tells you to 'stop' ...

 

Looks good to me. I have a Petromax that has a slightly dished bottom. It will wobble when set on a flat surface. Kind of unusual for a Petromax but I guess it can happen with any lantern.
Very nice looking lantern!

 

This was a March 1979 X246B with a 'blown' base. I cut it open recently to recover the fittings for a project. The damage was not all the way around the base but clearly 'not good'.

Iain

 

@Sedgman Yes, when they’re “Blown” they are an accident just waiting to happen.
Thanks for sharing this photo, it’s graphic evidence of the structural damage caused by over pumping.
Cheers
Pete

 

You’ve made a nice job of your X246B, what are going to do next?......

Stevie

 

I'm currently looking around for something. A very nice Anchor turned up at our local boot sale at the weekend but I'm really looking for a British brand so I passed on it.