Holes in the side of buffer bottles

[JamesDavies]

Is it acceptable to drill holes in the side of regular 2kg Ali fire extinguishers? My concern is that I might compromise the tensile strength the round bottle has if I merrily drill a giant hole in it

Cheers,
James

[geeza]

I assume this is to add a fitting to the side of the bottle. I would advise against it, the wall thickness is about 5mm. This is not enough to tap for a decent BSP thread. Then ends of the bottle are thicker, this can be done. But to pass the rules it should be pressure tested and certified as a custom component.

[maddox10]

Not a good plan. It does compromise the strength greatly.
I have seen buffers with the wall strengthened with a welded on plate to have a thicker wall to be tapped.
Rule of tumb. For aluminium 1/2bsp needs 14mm of thread. 3/4bsp 20mm and 1"bsp 25mm.

If the couplings are removed and remounted on regular basis, it is better to have a steel or bronze insert.

Easier option is to use the already available threaded hole with an adaptor.

[JamesDavies]

Cool, thanks guys. In that case I'm thinking of reinforcing the fittings with a steel band that fits tightly around the bottle and fitting to relieve some pressure from the threads.

[terry]

Can't you fit it to the base ? You can use a 1/4" bsp fitting and put a steel locknut inside then.

[JamesDavies]

I can and that's what I've been doing up to now, but that means lying the bottles length ways, making the bot very long. Plan was to turn the bottles 90degrees and plumb out the side, then cut the bot shorter Yeah, I was going to look into how easy it'd be to get a locknut inside the bottle- could be a challenge!

[maddox10]

In Bullfrog I made a steel buffer to fit the space we had.
A tad heavier than an ali bottle, but the easy of making it and the cheapness of the material compensated hugely for that.
And the added value of having it as a part of the frame is nothing to sneeze at.

[JamesDavies]

Yeah? Did you turn it yourself from a block?

[maddox10]

It's a steel tube with welded on couplings and lids. Pressure tested by the firm that delivered the steel tube.
I worked there 2 decades ago, and I still have good contacts there.

[WHS]

In the pics I've seen of Bullfrog, it looks as thought the tube is welded across the chassis as a structural member and the hardox sides of the chassis become the end caps of the buffer tank. Is this so?

[maddox10]

The buffer is integral to the chassis/armor but the endcaps are not the hardox sides, but welded in caps.
The buffertank was pressuretested before and after the welding to the chassis/armor.

I contemplated using the armor as pressure stressed, but refrained from it as any battledamage to the armor would compromise the safety.
In the end, the welded in end caps add "only" 300 grams.