This is a complex model, representing an early steam engine made by Newcomen. The type was commonly called an atmospheric engine because it relied on the condensation of steam to create a partial vacuum under the piston, which was then pushed down by atmospheric pressure. The engines were mainly used for pumping water out of mine shafts. This is a somewhat stylised model made of mainly wood and brass, but it works in the same way using similar mechanisms.
It was supplied as a kit of materials with instructions. Most of the metal parts were supplied as raw stock or partially completed parts. Most of the wooden parts were supplied ready shaped, except the beam itself, which had to be cut from block. Overall dimensions of the completed engine are 440mm high and 265 x 130mm base.
The burner supplied is a standard Wilesco Esbit burner tray. However, I have found the engine works better using a meths burner and have tested it using one from a Mamod MM2. It is situated under the boiler, which is supported by a brass stand surrounding the burner.The boiler was supplied partially completed and appears to be a gardening atomiser! It is a pleasing shape and is perfectly adequate for the very low pressures used in this engine. Finishing consisted of fitting a safety valve, overflow plug and a top cap with a feed pipe. It's dimensions are 82mm diam x 75mm height.
The steam feed is connected to the bottom of the cylinder via a rotary steam valve. The cylinder is 1" diameter. Because there is no crank to define the length of the stroke, this is variable but is approximately 1" when working normally. The piston supplied was a plain aluminium disk. It was rather sloppy and allowed much steam to escape past it so it has been replaced by a more accurately machined brass one. The piston rod exits from the top of the cylinder and is connected to the beam with brass chain.
Also connected to the same end of the beam with brass chain is a weighted rod which operates a complex linkage. This linkage opens the steam valve and closes the water valve at the bottom of the piston stroke. These two valves are latched in this position and remain there as the piston rises and steam enters the cylinder. When the piston reaches a restriction at the top of it's stroke the steam pressure starts to rise. This pressure raises the piston in a second cylinder. This second piston releases the latch on the valves. When released, the steam valve closes and the water valve opens, allowing a jet of cold water from the top tank into the main cylinder. this causes the steam to condense rapidly, creating a partial vacuum under the piston. Atmospheric pressure then pushes the piston down, relatching the valves and repeating the cycle. At the bottom of the stroke, the condensate, along with the water from the jet, is forced through a (deliberately) leaky non-return valve into a small tank, from where it drains into the main water tank.
The other end of the beam is connected by another brass chain to the piston rod of a pump in the main water tank. This pumps water up to the top tank for condensing purposes. In the real world, this would be the main pump, raising water out of the mine shaft, only a small portion of which would be used by the engine.
I had many problems building this engine and it still is not working properly. A blog of the build process can be seen on the UM&OS forum here