Brake Tests

46 (g) Margin of capacity to insure proper operation under unfavor- able service conditions and to enable future demands to be satisfactorily met without radical changes or loss m efficiency in any direction. FUNDAMENTAL PRINCIPLES IN AIR BRAKE DESIGN. 96. A satisfactory brake must possess reliability, flexibility and effectiveness. . , , 1 rornicite Reliability or certainty of operation is a fun am tal requisite, depending upon correct design and reasonably good maintenance. The essential principle is that any variation from normal condition must tend toward an automatic application o e brake an i not tend to render less certain the obtaining of a brake application w desired. Flexibility involves: , x . 1 Lralino forces (A) Extension of time in which to obtain predetermined braking forers. (a) Range between zero braking force and maximum braking force. (b) Proportion of reservoir and brakeeylin er volumes, pressure (c) Low degree of braking force per unit of brake cylinder pressure. (B) Flexibility is obtained in Prostkalerics brake application (a) Fixing the time required to o seconds to 69 seconds. With at a minim brakes this time will necessarily be pneumatically controlled b is longer than will permit of longer in propor ion asth through the equalizing discharge the of thePbrakc valve at a faster rate than the equalizing valve of the bratsvreduced. With electrically controlled reservoir is be ngecudent of the length of the train, brakes this time is indent between the initial and final brake (b) Fixing a range of 20 port to obtain this full service brake pipe pipe pressures requires reduction, and reservoir volume to the brake (c) Proportioning the aux y (standard piston travel) so cylinder and clearance volumes (stand the auxiliary reser- that the actual equalization D 70 pounds initial brake pipe voir and brake cylinderdis (theoretically calculated equali- pressure will be 50 poun 0 pounds allowance being made zation pressure 52 pounds, 2 pounds a for losses). braking force per one pound (d) The development of 34 per ■ rak brake equipments and brake pipe reduction for passenger reduction for freight 3 per cent, per one pound brake pip brake equipments. Effectiveness involves: (A) Service. . . dictent with flexibility (a) Maximum degree of braking force co requirements mentioned above.