THE HYDRAULIC DYNAMOMETER 



793 



A casing C, carrying a double series of pockets similar to those on the 

 disc, in the same planes but facing in the opposite direction, surrounds 

 the disc and carries a graduated lever L from which are suspended the 

 weights comprising the brake load. 



The shaft passes through bushed openings in the casing which it fits 

 closely so as to prevent undue leakage. 



In the case of an 18-inch brake wheel the wheel itself carries twenty- 

 four pockets on each face, while the casing carries twenty-five similar 

 pockets. These are 4J inches in radial depth and have an axial width of 

 1J inch, the dividing vanes 

 or partitions being j- inch 

 thick. 



Provision is made for 

 supplying the pockets with 

 water, and for allowing this 

 to escape after having work 

 done on it in the dynamo- 

 meter, while a small air 

 vent is provided in the 

 thickness of each vane to 

 admit air from an annular 

 chamber K in the casing 

 to the centre of the circle 

 formed when two of the 

 pockets on disc and casing 



FIG. 



Stroke 



398. Pressure Diagrams from 

 Hydraulic Brakes. 



Cylinders of 



As originally designed by Mr. Froude 



directly face each other. 

 It is to this detail that the 

 brake owes its successful action, 

 these air vents were absent. 



The action of the dynamometer is as follows : Water admitted to 

 the casing through the flexible rubber tube at T finds its way through a 

 series of four holes in the boss B into the chamber E between the discs, 

 and thence through a series of small holes F F, formed in the thickness 

 of the wheel vanes, into the pockets. 



To prevent the water being projected into the air holes the radius of 

 the inlet hole circle is made rather greater than that of the air vent 

 circle. 



Considering one of the pockets, its contained water is thrown out- 

 wards by centrifugal action, and, guided by the circular boundary of 

 the pocket, is projected forwards into a stationary pocket in the casing. 



