CONTINUOUS EAILWAY BRAKES. 



189 



Of the " Differential " pressure brakes, it will bo sufficient 

 to describe the " Automatic " vacuum brake, and " Steel & 

 Mclnnes " air-pressure brake, as they are typical examples. 

 Of the " Reservoir " brakes, the " Hardy " automatic 

 vacuum, the " Westinghouse " automatic air-pressure, and 

 the "Barker" automatic hydraulic pressure brake are the 

 most interesting types. 



"DIFrEEBNTIAL" PEESSUKE. 



The " Automatic " Vacuum Brake. 



An " ejector " on tho engine withdraws the air from the 

 continuous train-pipe, and from both sides of the brake piston, 

 Working in a cylinder placed in an enlarged tub ; the brake 

 pistons are thus placed in unstable equilibrium, and the 

 brake-blocks are " off." To apply the brakes, the driver 

 puts the ejector handle to " Brake on," thereby admitting 

 s^ii" to tlie train-pipe and lower sides of the brake-pistons, 

 sit the same time sealing the vacuum on the top side by 

 means of the " ball " in the valve, which is pressed against 

 its seat ; the brake-piston is thus pushed up, and the brake 

 applied. 



This vacuum brake complies in every respect with the 

 Board of Trade " requirements, and is the best of the 

 vacuum brakes. 



Its defects are, that on account of the large volume of air 

 which has to be withdrawn from the cylinders and train- 

 pipe through the ejector, tho brakes cannot be pulled " off" 

 •IS quickly as is sometimes requisite. 



The second defect is, that the same large amount of air 

 has to be admitted to the train-pipe for application of the 

 brakes, though in this case an automatic valve in the guard's 

 van is available, in addition to tho driver's valve ; hence 



