Re: Howitzer & Tank "Bustle" On Barrels: Purpose Of, And Function (gas extractor ?) ?

"Robert11" <rgsrose@xxxxxxxxx> wrote in
news:1JmdnTckHttIgs3fRVn-vA@xxxxxxxxxxx:

> Hi,
>
> Thinking about that "bustle" on large tank and howitzer barrels, and
> although I've read descriptions of it's purpose (to help in clearing
> out residual fumes), I realize i still don't understand how it
> functions. Think it might be called a gas extractor ?
>
> O.K., so there is a large gas pressure right behind the shell when
> fired. This pressure presumably enters the chamber provided by the
> bustle. But, this chamber, as I understand it, is not vented; just
> connected to the barrel interior by some ports.
>
> So, the pressure in the chamber is probably about the same as the
> pressure behind the shell ?
>
> Therefore, how does it work; I can't see how if it's about the same
> pressure as what's in the barrel after the shell leaves the barrel it
> does anything ?
>
> Obviously, I'm missing a lot.
>
> Might some please explain in detail how this functions.

It works because after the shell leaves the bore, the bore
pressure drops to ambient very quickly
The pressurised fume extractor has a not insignificant
amount of high pressure gas trapped and it makes its
way back out the forward slanted gas ports at high
speed. I won't go into details but suffice it to
say this high speed gas drags a whole lot of whatever
else in the bore with it ( by momentum and entrainment
if you want to get technical ).

IBM

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