Rotary Steam Engines: Page 4.

Updated: 8 July 2007

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ROTARY ENGINES OF THE 1870s.

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Stocker Rotary Engine: 1872
Left: The Stocker Rotary Engine: 1872

"The sector pistons are each connected through central concentric shafts to slotted cranks in which a sliding box and link connect to a crank on a shaft eccentric to the sector shaft. A differential movement of the sectors is produced while rotating which rotates the driven shaft by the outside slotted crank connections."

An example of the "pursuing pistons" approach to rotary engine design. Reuleaux says, that as a consequence of the large area between the outer surface of the pistons and the inside of the cylinder, "The joint between piston and chamber can without difficulty be made steam-tight,..."

From "Mechanical Movements, Devices and Appliances" Hiscox, 1899


SELECTED ROTARY ENGINES OF THE 1880s.

The four rotary steam engines below were illustrated in the US journal "Manufacturer & Builder" for June 1880. Extracts from the contemporary description are in green text. The seals and packings- usually the Achilles Seal of these machines- is highlighted in red or pink, where feasible.

The Pillner-Hill rotary steam engine .
Left: The Pillner-Hill rotary steam engine; cross-section. An English design of the "gear-pump" type.

"The Pillner-Hill has two cylindrical overlapping chambers, and two systems of rotary pistons, which may be compared to cogwheels. These wheels, by the close contact of their cogs, prevent the passage of steam between them, and they are adapted steam-tight to the interior of their cylinders by metallic packing in the tips of their teeth."

The Pappenheim pump appears again. This design appears to be reversible; by rotating the plug cock on the right steam can enter on either side of the rotors. There seems no possibility of expansive use of steam; it probably worked but it would have been dreadfully inefficient. The design is related to the gear-type oil pumps widely used in car engines. This was the type of engine built by Murdoch.

Anonymous rotary steam engine
Left: An anonymous design, (though it looks very much like the Birdsall Holly engine) again of the "gear-pump" type.

Once more the exhaust "eduction" pipe is no bigger than the inlet. The expansive use of steam looks to be impossible. Engines like this are inherently reversible, given suitable steam connections.
The design is similiar to the Roots blower widely used as a supercharger for IC engines.

Anonymous rotary steam engine
Left: Another anonymous design reminiscent of the Shorrocks blower, which was once much used for supercharging IC engines.

"...has four distinct pistons, which slip in and out in the eccentric hub."

At first this looks unworkable as the steam volume expands and then contracts again before the exhaust port is reached allowing no work to be done. However the pipe at the left may not be the exhaust, but an alternative steam inlet for reversing, and there is probably an exhaust port at the bottom, not shown in this contemporary drawing.
The twiddly bit on the right appears to be just a steam admission valve.

Anonymous rotary steam engine
Left: A anonymous rotary design that typifies a common approach to the problem; hinged "abutments" that swivel out of the way as the three "pistons" on the rotor go past.

"The engine has three pistons, two abutments, and two induction and eduction ports."

Here there is at least the possibility of expansive use of steam. However, note that the exhaust "eduction" pipe is no bigger than the inlet. This looks suspicious, but might just be bad drawing.
Rotary steam engine designers were very fond of "abutments" that swung out of the way (or were knocked out of the way) at convenient times, though they inevitably made the engine inherently non-reversible, like this effort here. Given that it has three pistons and two abutments, this might be the Cartwright engine of 1797.

The story of the Rotary Steam Engine continues on Page 5 of this gallery.

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