782 HYDBAULICS AND ITS APPLICATIONS 



a speed which is equal to or less than that of the engine according as the 

 eccentricity, of the ring R is equal to or less than the throw of the 

 crank H. 



(2.) Shaft H Clutched to Frame. This shaft being fixed, the cylinders B 

 are now constrained to rotate, the speed depending on the eccentricity of 

 ring R, and the direction of flow, and therefore that of rotation, being 

 regulated by the position of the rotary valve V. 



(3.) Shaft H clutched to Cylinders A. If now the eccentricity of li be 

 reduced to zero, no circulation of fluid takes place, and the cylinders A 

 and B are in effect directly coupled together through the medium of an 

 incompressible column of liquid and rotate at the same speed. As the 

 eccentricity of R is increased, the valve V remaining in the reverse 

 position, circulation takes place and cylinders B are driven backwards 

 relative to A to an extent which depends on the eccentricity. When 

 this eccentricity is the same as the throw of H the backward speed of B 

 is equal to the forward speed of A, and the actual speed of B relative to 

 the frame is zero, while by suitably regulating the eccentricity between 

 these two limits any speed lower than that of the engine may be given to 

 B and hence to the driving wheels. 



By the use of such a device the full power of the engine is available 

 for work on the driving wheels at all speeds of transmission, except in so 

 far as this is reduced by hydraulic friction losses produced by the circu- 

 lation of the working fluid. On the direct drive this is of course zero, 

 and it is only at lower speeds that it becomes important. At low 

 speeds it is not likely that the efficiency of transmission will be high, 

 while the difficulties consequent on any leakage of the working fluid are 

 obvious. The chief advantage of the system lies in its extreme flexibility 

 and in the absence of shock on changing speeds. 



ART. 209. THE HYDRAULIC BRAKE. 



The necessity for some braking apparatus by which the kinetic energy 

 of a heavy body such as a moving train or of a gun during recoil 

 might be quickly and safely absorbed without the recoil effect obtained 

 by the use of spring buffers, led to the invention of the hydraulic brake. 



In its simplest form this consists of a cylinder fitted with piston and 

 rod and filled with some liquid, usually oil, water, or glycerine. The two 

 ends of the cylinder are connected, either by one or more small passages 

 formed by holes in the body of the piston itself, or by a bye-pass pipe fitted 

 with a spring-loaded valve or with a throttling valve by which the area 



