| January/February 1961

Route 1 Bucyrus, Ohio

I promised to write about the Atmospheric or Vacuum engine shown on page 13 of the Sept. ALBUM.

I believe you will find that it is not a 'Hot Air' engine, it is more properly known as an Atmospheric engine. It has a much different operating cycle than a hot air engine.

This engine was manufactured in Dayton, Ohio, as a toy and is called a 'Vacuum Rotor' The operating cycle is roughly this, the first function of the cycle is the opening of the admission valve. This occurs just before the piston reaches the head end dead center, then as the piston starts toward the crank center the torch flame is drawn into and fills the cylinder with flame (incandescent gases that is, gases so hot that they glow). Just before the piston reaches the crank end dead center the admission valve closes thereby cutting off the flame.

Now, as we all know, when an unconfined gas is heated it expands or if it is confined its pressure increases and conversely if while confined it is cooled it produces a partial vacuum.

Now back to the engine. We have a cylinder filled with incandescent gases and we have suddenly closed the valve and instantly the flame in the cylinder is extinguished and the heat of the flame is absorbed by the cylinder walls and is then in turn passed to the atmosphere by the fins on the cylinder in air cooled engines or into the water on water cooled engines. The Vacuum Rotor has a small pocket on top of the cylinder for this purpose.