basic idea here is pretty simple. An existing gas pressure regulator
has the valve removed and the back tapped for 1/4" NPT. We re-use
the diapragm and adjustment bits, spring, etc and the diapragm acts on
a reach rod, which lifts a ball off the seat several inches above.
This keeps the heat of the steam away from the diapragm, since the steam
simply condenses in the 6" length of 1/4" pipe. I used
a 3/8" ball end-mill to cut the seat in the stainless plumbing bits
for the ball. The only difficulty I have with this is that it
sometimes buzzes a bit; this is probably because there's water in the steam.