|Some Bash Valve Steam
The original bash valve experiment is
based on a 31cc two stroke. I was
trying to see if I could vary the cutoff
by changing the distance the ball
traveled after being lifted from its
The valve is a 440c stainless ball 5/16 in diameter with a hardened steel seat made
from a drill guide bushing which was pressed into a hydraulic fitting.
In this exploded image:
The hardened drill bushing seat is pressed into the hydraulic fitting on the left. The stainless 5/16
ball is caged by the piece next to it that looks like it has four holes. The cage is a hexagonal piece
with a hole the length of it large enough to let the ball travel. Each face of the cage has two holes
drilled to feed steam.
The cage is held in place by the threaded fitting next to it, which has a hole the length of it that
allows the threaded rod on the far right to protrude down into the cage.
The threaded rod that goes through the brass elbow is an adjustable rebound stop for the ball. The
idea is that when the ball travels a long distance up and back the engine experiences long cutoff
and therefore high torque. Reduce the travel (and therefore time) and the cutoff is reduced.
Does it work?
It does. With long cutoff the bash valve engine will run with as little as thirty pounds of air. If you
reduce the cutoff to only the length of the lift, which is set at .030, the engine requires around a
hundred psi to run. The ball valve dynamics are readily apparent in listening to the engine run. The
engine runs fairly smoothly as torque increases with a lengthening of the rebound distance, until a
point near full torque where the ball begins to bounce erratically and the engine runs rough. A further
increase in rebound distance results a smoothing of running but an obvious flattening of the torque
curve where it is clear the valve is open nearly all the time. Perhaps a video is in order...
Will it last?
I doubt it. It has probably four hours of run time on both steam and air at varying speeds and loads.
The lift pin (which is drill rod), seat, and ball all show no wear as yet, but the mild steel rebound pin is
dished and swelled. If you don't require reliable lengthy run times, this is a simple and inexpensive
solution for a high temperature and speed engine with variable cutoff.
Here is a 30 meg video of a setup run
for the improvised Prony brake. With
90psi the engine operates from 4500
rpm down to around 900 with max
power apparently around 1900. I
guess that shows that the valve is
undersized for such low pressures. It
measures 2hp at 90 psi if I'm doing the
26.5 inch arm
2.5 lbs force
Drill bushing hard seat
I have some silicon-nitride balls and tungsten carbide
seats to try out...
Perhaps I will try high pressure and heat steam though my
focus has largely moved to the v-twin.
Prony Brake Formula=
HP= Length of Arm in Ft X Arm Force
in Pounds X 2Pi X RPM... all divided
What I copied:
Bash Valves Pros and Cons-
· Mechanical simplicity (cost)-
· Short Cutoff (high efficiency)-
· Lubrication free-
· Speed tolerant-
· Lack of variable cutoff-
-Longevity is a function of speed… make a high displacement, low speed engine or plan to
replace the valves frequently.
-Variable cutoff … accept the torque curve the bash valve gives and mitigate with a gear
train or find a way to cushion the steam closed valve.
Here is a link to an article on the
Carter's bash valve system, which is a
system worthy of study-