Westbury explains that the special feature of the Grasshopper engine is the use of a single ended beam anchored from one end, instead of being pivoted on central trunnions, as in the orthodox type of beam engine. The advantage of this arrangement is that the working end of the beam can be connected directly to the piston rod of the engine, and in this way it is possible to make the engine much more compact especially in the matter of height, as it eliminates the space taken up by the usual swinging links between the beam and the piston rod crosshead.

The length of the beam, or lever as it is called, can also be reduced; whereas in the normal beam engine the beam is usually at least three times the stroke in total length, that of the Grasshopper is generally about 1 3/4 times the length of the stroke and its weight is also proportionately less.

The working end of the beam is guided in a straight line by means of the usual parallel motion device, suitably modified for this particular purpose, and it is, therefore, necessary for the anchored end to be capable of lateral movement. This is provided for by a swinging link arrangement, which was usually made in the form of a cast rectangular frame with lattice, or cross strutting.

Although the weight of the Grasshopper beam is completely unbalanced, the fact that it is much lighter than the orthodox beam enables engines of this type to be run quite satisfactorily at higher speeds than the former type. The compactness of the general engine structure provided inherent rigidity, and also simplified mounting and installation, with very simple ashlar or brickwork foundations. The engines were, however, often sunk into the floor, or elevated to give space for an air pump and condenser under the bed and a race was provided to give clearance for the flywheel.

CLICK ON DRAWINGS TO DOWNLOAD - FOR PERSONAL USE ONLY. FOR INDIVIDUAL COMPONENT DRAWINGS, DOWNLOAD AND SELECT ‘DRAWING VIEW’