|A two cylinder bash valve engine using off
the shelf valves-
Here is a converted air compressor I'm almost done with. I'm going to try to use some off the
shelf valves hoping for high efficiency and longevity.
The compressor is a Harbor Freight 5hp V-twin. It is single stage so the cylinders are the same
size. Who knows if it will hold up...
The cylinders were drilled for uniflow exhaust and heads were made to host the valves. A drill
rod lift pin was installed in each piston.
The valves are the discharge valve assemblies off of a CAT water pump. They are kit number
30686 and they fit 280, 290, 333, and 430 model pumps.
They are hardened stainless and they are designed for similar duty though in water instead of
steam. They have a much lower mass to surface area ratio than a round ball and should last
longer for it. The center spring holder is plastic and has to be replaced with steel.
The valves consist of a cage with a travel limiter that also holds the spring, the valve itself, and
a tapered seat. The assembly is installed and sealed by clamping force.
I've run the engine briefly without manifolds and what it mess it makes! It idles nicely at 100 psi
and 400 degree, picks up at 150 psi and 500 degrees and really hums at 200 psi and 600
degrees. Not real scientific, but its encouraging. I'll rig up the Prony brake and give the specs
shortly. There is a 18 meg movie of a test run.
The spring may anneal quickly so I may need a higher heat spring. Inconel x750 or Rene 41
would be good candidates for high temperature springs, though I haven't found any 'off the
A return spring is important for longevity because it prevents the valve from leaving the lift pin.
If the valve leaves the pin it will be returned to its seat by steam velocity, which is much, much
higher than the piston speed the pin is operating at.
See Steam Automobile Volume 26, number 4 (SteamAutomobile.com) for an article by Peter
Barrett on the issue of bash valves staying on the lift pin.