This is a reproduction of the Duplex Vacuum engine that was
during the period of 1900-1920. As descriptions go, the name is
The engine type is a Heinrici Stirling variation, but the name might
make one think it is
some type of vacuum engine. Since the originals of this model
were made by a company
called the Duplex Vacuum Company, who made vacuum cleaners, this
is named for that company.
The person responsible for the design of the engine was one of the
There were two of them involved, and I don't know which designed the
were produced in a fair number, and examples are still seen today.
I built this particular one using a Taig manual milling machine for all
the milled parts,
and the turned parts were made using Taig and Atlas manual
lathes. No CNC machines.
The power piston is made of graphite, and power cylinder is aluminum
sleeved with 360 brass.
The displacer end cylinder is 416 stainless, and the displacer piston
The base is 1018 CRS made in four pieces and silver brazed together.
The crankshaft runs in small ball bearings.
The fan and pulley on the one side of the engine were not part of the
prints, but I thought the
fan would help cool the finned power cylinder.
Prints are from Jerry Howell. He's passed on now, but his family still
run the business as he did,
and sell his complete product line of prints and other things for model
engine builders. Prints for
this engine are available on his web site.
I spent three months on the construction, (part time!), coming to about
250 hours total.
Here is a short
video of the engine running. The camera work
is a bit jumpy as I was changing the fan belt as
the engine was running in order to slow down the fan a
bit. After the fire is extinguished,
the engine continues to run for some time on the residual heat in the
displacer end of the
cylinder. The heat is provided by a very small propane burner
inside the firebox. That burner is also
featured on the main page, linked at the bottom of this page, and was
built, again, from Jerry
It will run
much faster if the flame is turned up on the burner, but then it starts
getting hot fairly
fast. Once it gets just so hot, it will start to slow down
because the fins on the cylinder cannot
dissipate heat fast enough to run efficiently.