On Mon, 14 Nov 2011 13:11:29 -0800, engineman wrote:

I built a propane fueled steam powered cycle.
http://www.youtube.com/watch?v=cVn00...eature=related Now I want to
add a pressure control to turn the gas flow down or off when the
pressure of120 PSI is reached. It would be too clumsy to use a regulator
from a large boiler, I need a small device that would work with a valve
using 1/8" pipe threads. I also would like to avoid electrical devices
so as to eliminate the need for batteries.
So Does anyone know of a source of a device like this or plans to build
one?

Engineman

piston == valve == spring.

Supply the piston with pressure from the boiler, and arrange it to close
the valve. Crank the spring down for more pressure, let the spring off
for less. (Come to think of it, you should be able to use a diaphragm
instead of a piston, like compressed-air regulators do. The difference
is that instead of the diaphragm actuating a valve that supplies itself
with pressure, it'll be actuating the gas valve).

Expect imperfect operation in the form of lag and pressure variations: if
the thing's just sitting there steaming gently and you nail the throttle
the boiler pressure may go down quite a bit before the burner makes it
catch up. Similarly, if you ask for extended high power output (climbing
a hill, or going fast), then the boiler pressure will sag and stay sagged
until you park the thing again.

You can fix the long-term sag somewhat by making the valve more
sensitive, until you make it so sensitive that the lag induces
oscillation.

But as long as you've got wiggle room above and below 125psi, you should
be OK.

--
www.wescottdesign.com