574 HYDKAULICS AND ITS APPLICATIONS 



Of all variable power engines, that of Mr. K. Kigg 1 has achieved the 

 greatest success in practice. 



This engine is provided with three cylinders, fitted with plungers which 

 are pivoted at their outer ends to an external cylindrical ring, which is 

 itself keyed to the driving shaft. The cylinders face radially outwards at 

 120, are single acting, and are rigidly fixed at their inner ends to a ring 

 which rotates on a fixed hollow shaft forming the supply pipe, eccentric 

 with the external casing, and carrying the inlet and outlet ports. 

 The rotation of the outer ring is thus accompanied by a reciprocating 

 motion of the pistons in their cylinders, the stroke of each being twice 

 the eccentricity of the two rings. There are three ports, one to each 

 cylinder, and as these rotate each in turn is presented before an inlet and 

 an outlet port in the central hollow shaft. Regulation of power at con- 

 stant speed is obtained by altering the eccentricity, and therefore the 

 stroke of the engine, by means of an hydraulic relay governed by a centri- 

 fugal governor. The reduction in water consumption is thus proportional 

 to the reduction in the stroke. When regulating the eccentricity by hand, 

 at constant power, a decrease in stroke will be accompanied by a corre- 

 sponding increase in speed, the work done per second then being 

 approximately the same. This method of working may be adopted for 

 capstans and the like, where when hauling in slack, etc., a rapid rotation 

 with very short stroke is required, while when the full pull is to be exerted 

 by the rope, a long stroke and slow rate of rotation is essential. By revers- 

 ing the relative position of the centre the direction of rotation is reversed. 



The speed of the engine may be anything up to about 500 revolutions 

 per minute, though probably 250 revolutions marks the limit of its really 

 efficient performance. At the latter speed the inventor claims to obtain 

 efficiencies up to 80 per cent., though this value would appear to be 

 improbably high. 



In the Armstrong type of engine, oscillating cylinders mounted side by 

 side and driving on to a common crank shaft are adopted. Three cylinders 

 driving cranks at 120 are usual, and are fitted, either with externally 

 packed rams forming a single acting engine, or with differential rams 

 having areas in the ratio 2:1. The smaller of these is exposed to a con- 

 stant pressure head, and the engine becomes double acting with equal 

 efforts on each stroke. The single acting engine is more commonly used. 

 Admission and discharge take place through a circular slide valve working 

 within the hollow trunnions which carry the cylinders. This engine is 

 made to develop up to about 70 B.H.P. 



1 See Engineering , vol. 45, p. 61. 



