05 August 2010

Wooden air engine - 2

This post is part of a series inspired by Matthias Wandel air engine.

Matthias Wandel air engine is square, as it is made out of plywood. Looking in older books, in this case Mechanical Movements Powers and Devices by Gardner Hiscox, I found two examples of a square piston steam engine.

For Root's square piston engine,  no details are shown for the valves,  but it is possible to imagine rotating valves linked to the crank shaft.  When implementing this in wood as a low pressure model, a possibility to minimise friction torque is to give the valve a small diameter. At the same time leaks between in and out stream must be minimal. I see two possible solutions here, one is to put one valve at each side of the engine,  the other is to use a hollow shaft and use it as the exit port.
An alternative is to try to implement a solution close to the oscillating cylinder steam engine as both engines have points in common, in this case a translating (sideways moving) 'cylinder'  for the vertical one and ... something even more clever for the horizontal 'cylinder' as it contains a piston with sideways moving parts. It is probably a though problem as the valves for the horizontal and vertical cylinders must stay separated.
The drawing is strange as the crank shaft (b) seems to hit the top of piston C when rotating.  To avoid this  the shaft could be made of a rotating disc embedded in the sides.

The Dake square piston engine,  in this case I found  more information as thousands of them where made between 1887 and 1950.  The engine is impressive as it offers a 4 piston continuous torque engine with only four major moving parts.  As a model it would be less impressive as even a flywheel is superfluous. It is more a pizza box with a shaft in its middle.
Looking at the drawing from the patent, there is apparently a rotating valve embedded in the cover feeding the 'cylinders' through the piston.

To finish a quick sketch of the rotating valve I had in mind for Root's square engine as I am certain I will have forgotten all about it within a week. The air comes from a feeding ring directly through the valve and leaves via a covered opening towards the shaft.  The opening angles of the valve must probably be more than on the sketch,  is it 90°?

[edit] There is an animation of Charles J. Dockstader  for the Dake engine showing the steam distribution through the inner piston.