[Phys-l] fire pistons

[John Denker <jsd@av8n.com>]

This is a practical application of compressing a gas
quickly enough so that it is approximately thermally
isolated from the surroundings.  Useful for making
fire without matches.

Evidently these things have been in use for thousands 
of years:
  http://en.wikipedia.org/wiki/Fire_piston

Here are detailed instructions for making one out of 
PVC and wood, without any special tools:
  http://www.wildwoodsurvival.com/survival/fire/firepiston/rbmodelt/index.html
including a video of the thing in operation:
  http://www.wildwoodsurvival.com/survival/fire/firepiston/rbmodelt/ModTVid.wmv

The jig for cutting the O-ring groove is cute, but
I would just chuck up the 7/16ths dowel in a 1/2"
drill, put the drill in a vise and call it a lathe.
A 1/2" drill is not that hard to come by.

I've never actually made one, but I think I would prefer 
Schedule 80 CPVC since it has thicker walls and higher 
pressure ratings than the more common Schedule 40 stuff.
Available from plumbing supply stores, not from Lowe's
or Home Depot.
  http://www.harvel.com/tech-specs-pvc-pipe-80.asp
or even
  http://www.harvel.com/tech-specs-pvc-pipe-120.asp
as opposed to
  http://www.harvel.com/tech-specs-pvc-pipe-40.asp

Another option might be to stick with Shedule 40 and
then somehow reinforce the last inch or two, which 
is the only part that sees the highest pressures.

Also I would be tempted to scale the thing down from
nominal 1/2" barrel to nominal 3/8", just to make it
stronger, lighter, easier to carry, and easier to
operate.



Here are instructions for a smaller metal fire piston:
  http://www.burghscouts.com/Flyers/FirePiston.pdf
  www.youtube.com/watch?v=kg9rRDMuY78