Brake Tests

195 average that could be obtained from all the stops made under the various test conditions and the dotted lines the average of the best stops. 6 000 ■ . 399. The lighter upper portion of three of the curves in Fig 115 indicates that no test records were available to justify this DOT: curves. However, the general shape of the curve,'determined from th" stops which were obtained at the lower percentages of brakinc om the justifies the extension of these curves to the higher percent-,» g power, power, as shown by the lighter lines, and we feel percentages of braking by the extension are correct. that the values shown 400. In making comparisons between the curves Tf...- 2 and No. 3 clasp brakes it should be borne in mind that tl or the No. under which these two brake riggings were tested what the conditions ferent and a direct comparison between the two curves somewhat dif- fication, cannot be regarded as indicating the relativ Without quali- of the two types of brake rigging. For exemple relative performance ment of the No. 3 clasp brake gave a slightly The rigging arrange- braking power per pound of brake cylinder pressure er percentage of the No. 2 clasp brake (see table, page 125). Consequent ! • that of the cylinder pressures obtained with the two sec ntly, even had the No. 2 rigging would have been at a slight RERES been the same, being braked at a slightly lower percentage. It is 5 antage due to its for this difference by assuming that the stops proper to compensate in the same relation to the difference between the aid have been shorter percentage of braking power as is established for a and the proper in braking power by the curve (Fig. 115). Similar difference 401. In addition to the above, the condition of the , ., known to be different in the two series of test the brake shoes, if should be allowed for. However, when testing the tiuder comparison, although the shoe conditions were on the whole bett t ° clasp brake, information which had accumulated from the test er known, due to the impossible to point to any particular circumstance preceded, it is affected the value of a comparison. The cooling which appreciably of the No. 3 clasp brake car with water is the chief the brake shoes noted. Laboratory tests showed that the difference difference to be of the brake shoes, when cooled either by water or a' 1 in the condition effect on the coefficient of friction and the consente as no appreciable able, however, that when water cooled the warning tstops, it is prob- tend, if anything, to impair the bearing area and eon / the shoe would stop might be expected. Thus, while a comparison sequently a longer with the No. 2 and No. 3 brakes mav le Spa between the stops F . brakes may be unfair to the latter : - 2 that for practical purposes the comparisons made he latter, it is felt ■ally affected, had the shoes on both cars made we uld not be mater- treatment. a cars received the same cooling