Shay Operation -
Initial: 10/17/06 Last Revised:
The shay is near the end of the third summer and it seems to run pretty
well. The major limitation is the power output
of the boiler system. There is no problem on a relatively flat
track. However on 3% or greater grades with a large load the speed
is limited to about 12 scale mph. ( Note that with the prototype, 12 mph
was about top speed and on a 3% grade it'd be going half that or less.)
The shay runs at Mill Creek
Central which has lots of hills. There are usually some
large steamers as well as diesels running so it's simple courtesy to run
fast enough to not hold up the others. The boiler output is limited
by the boiler design. The challenge is to get the maximum steam from
Simply put, the goal is to produce the maximum energy. This
goal can be accomplished by burning fuel at the maximum possible rate
and at the same time extracting the maximum heat from fire. After
fooling with several burner evolutions it was useful to list what was learned (this is probably obvious to an experience fireman):
- Fuel - Oxygen Mixture: If the mixture is too lean
(too much oxygen, too little fuel) the fire will likely go out.
If the mixture is too rich (too little oxygen, too much fuel) the fire
gives off a heavy black smoke and quickly fills the flues with soot.
If the proper ratio of fuel and oxygen is present, then
the fuel will be completely consumed and little or no smoke will be
given off and there will be little or no build up of soot in the tubes.
- Draft: Draft refers to the current of gases that
flows into the firebox and then out of the firebox through the flues and up the stack. If there is
insufficient draft, insufficient oxygen will be draw into the firebox
and the fire will burn rich (black smoke & soot in tubes).
If the draft is too great, the fire may go out. Another
undesirable effect of too great draft is that the gases leave the
firebox and flues at too great a rate and too much heat goes up the
- Forced Draft: The draft is forced by the engine
exhaust and the blower. The blower has the most effect. The
exhaust nozzle is quite large for the exhaust volume. This is
good in that there is little back pressure thus improving engine
efficiency. Because the draft is primarily controlled by the
blower, the proper mixture is not effected much by changes in throttle
- Blower Holes: Ken Schroeder specified 1/32"
blower nozzle holes in the blower ring. In the earlier
operation there was a problem with these holes plugging so they were enlarged
to ~0.050". This increased the amount of steam required for
the blower function and reduced efficiency. The holes were
plugged then drilled 1/32" to match the drawings.. This
improved the blower function. There seems to be no problem with
the holes plugging if an overly rich fire is avoided.
- Closing the Fire Pan: To avoid excess draft and the
associated heat loss up the stack we want to limit the air
entering the fire box to the minimum required for proper combustion.
This can be achieved by closing all holes in the fire pan except the
entry point of air to be mixed with the fuel.
- Mixing Air & Fuel: Air that supplies the oxygen
for combustion must be mixed with the fuel. This is true for
both oil and gas fired burners. The better this mixing action,
the better the burner efficiency.
|Sievert 2960 Burner: The photos
at right show the large Sievert burner used for silver soldering
large pieces. It has a maximum output of ~ 400K BTU and can be
reduced to about 50 K BTU by reducing the gas pressure.
The lower photo shows the brass fittings at the back of the
burner. The fitting on the right has the gas orifice.
The fitting on the left is the mixing chamber. The fitting on
the right screws into the right end of the mixing chamber with the
front of the orifice just to the right of the holes in the side of
the mixing chamber. The gas shoots through the mixing
chamber and picks up air along the way.
|Burner Mixing Chamber: It was a small
step to copy the Sievert 2960 mixing chamber. The
drawing on the right shows the design. The chamber was fabricated
from 1" diameter brass rod. The nozzle
(copied from Bob Reedy's design in the May/June 2003 issue of
Live Steam ) fits into the
5/8" hole on the right end. The 7/8" diameter left end is silver
soldered into a hole in a ~1.5" X ~ 3" X 1/8" brass bar. The
brass bar with mixing chamber is attached to the front of the fire pan with a
couple 6-32 stainless screws and nuts.
|The photo at right shows the bottom view of the new mixing chamber
installed on the shay fire pan. The nozzle slides into the
chamber so the the tip is at about the middle of the air inlet
holes. The nozzle is held in position by the 4-40 socket head cap
screw in the bottom of the mixing chamber which serves as a set
Burner Operation: The first tests of the burner
were made on the test stand. After fooling with it a while
the best operation seemed to be with:
The fire is not very sensitive to the atomizer setting
but is very sensitive to the fuel and blower settings. For
example, a slight increase in fuel setting or slight decrease in blower
such as back to 25 psi will cause the fire to smoke. If the
fuel is increased very much beyond this setting the fire will smoke even
if the blower is increased to over 60 psi indicating that these settings
are near or at the maximum possible heating capability of the firebox
After the boiler had been up to ~110 psi pressure for about
20 minutes the following temperature measurements were taken using an
The temperature at the top back of the boiler was 345 F.
The temperature on the side of the smoke box was 310 F.
The temperature at the base of the smokestack was 345 F.
By contrast, the first fire pan design had large
openings around the nozzle which admitted much more air into the
firebox. With that design and similar fuel settings the temperature at the smoke box base
measured between 450 F and 500 F.
This burner seems to be much more efficient.
The first test at the track went very well. The
fire went out once when the throttle
was opened the first time and a slug of water blew out the exhaust pipe. It was a very
cold day (high 40s) and there was time for only about one hour of operation.
The burner seemed to operate well. A week later the shay
was operated a couple more hours and it continued to perform well. A
first time operator ran it for about an hour with no problem. The
fire did go out for him a couple times. Both times the fuel valve
had to be opened a little further to get the correct fuel input. The fuel
adjustment was probably required because the fuel level in the tank was
lower thus reducing the rate of fuel flow. The igniter relit the
fire with no problem.
The current plan is to use this design in the
Heisler. The mixing chamber might be made slightly larger by using
a 1.25" OD and 1" ID.
The same type nozzle will probably be used.
It would be nice to find a better quality fuel valve.