THE CONQUEST OF TIME AND SPACE 



of air not only allowed the brakes to act, but assisted 

 them in doing so. This was only the case, however, 

 when the emergency application of the brake was 

 made, this system of venting on each car into the brake 

 cylinder not being brought into play when ordinary 

 stops were made. Thus the engineer in this quick- 

 action automatic air brake has really two brakes at 

 his command, one for making ordinary stops, the other 

 for emergencies. 



In 1 891 a so-called high-speed air brake was per- 

 fected, this brake being really a modified quick-action 

 automatic brake. This modification consists of the 

 addition of an automatic pressure-reducing valve con- 

 nected with each brake cylinder. In the high-speed air 

 brake as applied when the train is running rapidly, the 

 highest possible pressure is applied at once to the 

 wheels, but this pressure is lessened by the automatic 

 pressure-reducing valves as the speed diminishes. This 

 method of applying the brakes is the most effective 

 way of getting the full benefit of their stopping power. 

 This high-speed brake, therefore, represents the high- 

 est perfection in train-stopping devices. 



We have referred here specifically to the air brake as 

 used on steam railroads. In another chapter the sub- 

 ject has been touched upon in connection with electric 

 railroads. In such brakes the compression of the air 

 is accomplished by electricity instead of steam, but the 

 general principles involved are the same as those just 

 described. 



It should not be understood that the Westinghouse 

 air brake was the only one, or the only type of brake, 



[146] 



