272 PC PASSENGER-BRAKE EQUIPMENT 



first installed or when new ones are applied, they should be 

 blown out with steam or compressed air before the valves are 

 attached, to clear them of foreign matter. 



If the distributing valve becomes dry from lack of lubrication, 

 or if it becomes corroded or very dirty, a greater difference of 

 pressure will be required to overcome the excessive friction and 

 to operate the movable parts. 



If the pipes and passages become corroded or very dirty, the 

 engine brakes will not apply and release as promptly as when 

 they are clean. If the engine brakes fail to apply when the 

 brake system is fully charged and a 5-lb. service reduction is 

 made, the trouble is most likely due to excessive friction in the 

 working parts of the distributing valve, which should then be 

 removed, cleaned, and lubricated. Sometimes the equalizing- 

 piston packing ring sticks in its groove and prevents the equal- 

 izing piston from being moved by variations in brake-pipe 

 pressure. 



PC PASSENGER-BRAKE EQUIPMENT 



DEVELOPMENT OF EQUIPMENT 



The schedule PC equipment was designed especially for pas- 

 senger-train service to control passenger cars weighing 130,000 Ib. 

 or more. Passenger-brake cylinders had been increased from time 

 to time as the increased weight of the cars demanded, until the 

 18-in. cylinder finally came into use. This brake cylinder pro- 

 vided for cars of maximum weight up to 127,000 Ib. When 

 cars of 150,000 Ib. or more were under construction, it became 

 necessary either to use a 20-in. brake cylinder or to redesign 

 the brake rigging so as to provide for a suitable brake for this 

 service. A very serious objection to the use of a 20-in. cylin- 

 der was the time necessary to apply the brake to its full 

 capacity. At 80 mi. per hr., the speed is 116 ft. per sec.; and 

 at 60 mi. per hr. it is 88 ft. per sec. A couple of seconds lost, 

 therefore, means a couple of hundred feet passed over before 

 the brake begins to be effective, thus greatly lengthening the 



