THE HACKWORTH VALVE GEAR.
Page 18
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A Concise Explanation of its Merits and Manner of Operation.
THIS radial _valve gear is fitted to the Yorkshire steam wagon, and the simplicity of. the gear will readily he understood from the illustration. The chief point about the mechanism is that one eccentric is used to do the work of two; whereas, in the more common type of Stephenson valve gear, two eccentrics are required for one valve, ene for forward gear and one for reverse gear. . The eccentric (AB) is at 180 degrees angular advance with .the main. crankpin (AC). A die is made to move in guides along a straight line (PD), when line DD is at right-angles with the centre line of the stroke of the piston the valve is in mid gear. The guides are fulcruined at E and can be turned to the right or left with the reversing lever; and rocking the guides over in either direction gives the full forward or -full reverse movenient respectively.
When the guides are in position as shown, the -eccentric at the crank end turns in a eircie and point E of the eccentric rod moves along line DD. The path of point G is an oval, and the point moving along this ,path gives the required mevernent of the slide valve.
The vertical dimension (XX) of this oval as shown equals the travel, of the valve in mid position, therefore, turning the guide round about its fulcrum (E) with the reversing rod in either direction increases dimension XX, and point G is so placed on the eceentric rod that when the link (GM is in positionas . shown the dimension XX equals 2 (lap pins lead) and dimension YY equals 2 (lap plus full port opening).