Model of Bell's Rotary Engine

Model of Patrick Bell's Rotary steam engine.

This engine shows one of the early attempts to obtain rotary motion from the pressure of steam without the intervention of a crank and connecting-rod ; almost the same arrangement was proposed in 1838 by Lord Armstrong as a water motor, and an example subsequently constructed gave off 5 h.p. at 30 r.p.m., with an efficiency of 95 per cent. A metal disc is secured to a horizontal axis carried in bearings, and the lower half of the disc is enclosed by a chamber of circular section having its axis a semi- circle. One end of this chamber is closed and provided with a pipe through which steam enters, the exhaust taking place through the open end. The disc is provided with three holes, each fitted with a circular plate turning on an axis radial to the disc, and these plates when set at right angles to the disc become pistons in the lower enclosing chamber. Toothed gearing is arranged to rotate these pistons into the plane of the disc on leaving the cylinder and back again immediately after entering, locking levers retaining them in position during the intervals. The steam pressure upon these pistons forces the disc round, but the engine is non-expansive, and although some provision for packing has been made, the leakage must have been considerable and the wear and tear excessive.