. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . ing througha compensator the direction of motion changes; , if a movesto the right, d moves to the left, or if there is compression in ahthere is tension in cd, and vice versa. Therefore this form ofcompensator can only be used with pipes which will withstandcompression. It has seemed impracticable to design an equallysatisfactory compensator for wires, although there are severaldesigns on the market. §393, BLOCK SIGNALING. 421 The change of length of these bars is so great
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . ing througha compensator the direction of motion changes; , if a movesto the right, d moves to the left, or if there is compression in ahthere is tension in cd, and vice versa. Therefore this form ofcompensator can only be used with pipes which will withstandcompression. It has seemed impracticable to design an equallysatisfactory compensator for wires, although there are severaldesigns on the market. §393, BLOCK SIGNALING. 421 The change of length of these bars is so great that allowancemust be made for the temperature at the time of the basis of 50° as the mean temperature, the pipes are soadjusted that the distance between the points b and c of Fig. 171is made greater or less than 22 inches, according to the tem-perature of installation. For example, if the temperature were80° and the length of the piping were 900 feet, the length of thepipes should be adjusted so that he is less than 22 inches by anamount equal to 900 X (80°-50°) X .0000065 = feet =. Fi«. 171.—Standard Pipe Compensator, inches. The length should therefore be inches in-stead of 22 inches. If the mean temperature was very different(say in Florida) some higher temperature should be taken asnormal, so that the extreme range above and below the normalshall be approximately the same. Guides around curves and angles. When wires are requiredto pass around curves of large angle, pulleys are used, and alength of chain is substituted for the wire. For pipes, whenthe curve is easy the pipes are slightly bent and are guidedthrough pulleys. When the angle is sharper, angles areused. The operation of these details is self-evident from aninspection of Fig. 172. 422 RAILROAD CONSTRUCTION, §394. 394. Track circuit for automatic signaling. The fundamentalprinciple of the track circuit method of indicating a track obstruc-tion or breakage, using direct
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