Oh, you can use a fire extinguisher valve easely enough as main bottle valve.

It's called "be creative". From gaffatape or tie-rip to keep the handle down, to bolt and wingnut, to strong servo's.

You also can use those fire extinguisher main valves as dump valve. Most have a treaded inlet on the inside, where the diptube fits in. That's in most cases a 1/8 bsp. Easy to hook up on the main feed line.

Chaos 2 used them to fire the weapon. So, in that respect those are the precursors of the ubiqtous Burkert.