AUTOMATIC SIGNALS.—The best known automatic signals are the Union electric signal and the Westinghouse pneumatic signal, both owned and manufactured by the Union Switch and Signal Co , and the Hall signal, owned and Manufactured by the Hall Signal Co.
The Hall Signal is described in ...1ppletoa Cr&Tullio of Applied _Mechanics, but certain changes have been made which permit the entrance of a second train into an already occupied section, while still maintaining a danger signal in its rear. This is accomplished by the inter vention of a combination of relays and track instruments, whereby the second train on passing the clearing track instrument for the section which it has just left cuts out the clearing track instrument- for the section which it occupies, so that the first train cannot clear the signal for that section.
The Union Electric Signal and the Westinghouse Pneumatic Signal both depend funda mentally on the use of the track circuit, which is illustrated in Pig. 5. The track circuit is a section of both rails of a piece of single track in which the ends of adjacent rails are connected by it piece of wire (see Fig. fi), and the ends of the rails in one section are insu lated from the ends of the rails in the section adjacent to it. In each section the ends of the two lines of rails of one end are connected together through a battery, while the two lines of rails at the other end of the section are connected by a re lay which controls the signal circuit. The presence of a train on any portion of a block, or the opening of a switch, or the breaking of a rail will interrupt the track circuit, and thus set the signal to danger, which is operated by it. So far this method is common to both systems.
The Union Electric Signal consists of a combination of clock-work and electric mechanism which is directly controlled by the track relay mentioned in the descrip tion of the track circuit.. The motive power consists of a heavy weight. In the past this signal has been built usually as a disk signal, with a continuous motion to the right. The demand for semaphores has, however, caused a change to be made in its form which has entailed certain alterations in the method of transmitting the motion from the operating mechanism to the vertical shaft on which the semaphores are mounted. This motion is now reciprocal instead of continuous. The present external appearance of the signal is shown in Fig. 7, the signal presenting alter nately the edge and surface of its two blades to the view of an approaching train. The blades, which are of the ordi nary home or distant signal form, as the case may be, are placed at right angles to each other on a revolving shaft, which moves through an are of 90° in one operation, and returns to its original position in the next. The mechanism operating and controlling this signal is outlined in Fig. 8. The rotary movement of the shaft, S. obtained by the weight passing over a sprocket wheel secured to it, is transmitted to one of a higher speed in a second horizontal shaft immediately above it, to which the cross, C, is secured by means of a large gear wheel and a pinion. The motion of this shaft, besides revolving the cross, C, causes a vertical shaft projecting through the top of the machine to revolve at the same rate cf speed through the engagement of two beveled gears secured to them. This vertical shaft is the one from which the signal banner is
operated. The C, on the intermediate shaft is that part of the driving mechanism by which its operation is controlled. The shaft, S, is the means by which the weight is wound up, and is also used to operate the device by which the danger position of the signal is insured when the weight has nearly run down. Secured to the frame of the machine is an electromagnet, if. and hori zontally above it is pivoted its armature bar, A, the outer end of which projects between two peculiarlyshaped levers, D and E, known as detent toes, and engages one or the other of them when they are elevated, depending upon the condition of the electromagnet. As shown in the cut, the magnet is demagnetized, and the detent toe, D, is held in the upright position by the armature, but should the magnet become charged and the outer end of its armature bar be elevated, the detent toe, D, would become disengaged and would drop upon the rest, I?, raising at the same time the hook, 11, from engage ment with the pin in the back of the cross, C, by striking a small pin, shown in the cut, located in the outer ex tremity of the hook, H. The cross thus released turns a quarter revolution, when it is again stopped by a second pin in the opposite side of its next arm, which engages with a second hook pivoted directly back of and on the same center as the first one. The detent toes are alter nately restored automatically to their elevated positions, and consequently the hooks, II, to their position of en gagement with the pins in the cross at each quarter turn of the cross. This arrangement entirely removes the strain and jar of the operating parts from the electro magnet, and reduces the friction in its armature bar to a very trifling amount, thus insuring great freedom in its action. On the main spindle of the machines a thread of a very fine pitch is cut where it projects through the front of the frame, and a cylindrical nut, provided with a pin of hard rubber on ono side, is placed thereon and held from turning by the guide, 0, but permitted to travel in the direction of the length of the shaft as it turns. As the machine runs down and this nut travels outward, the rubber pin in the nut approaches the point of contact between two springs through which the current the magnet of the signal is made to pass and causes their separation just before the operating weight has reached the bottom of the post, thus cutting off all current from the magnet, and thereby cruising it to stop in the danger position before the operating power is exhausted. A considerable momentum is gained by the revolution of the semaphore arm, which would cause heavy strains were it not taken care of. This is accom plished by separating the external shaft and semaphores entirely from the rest of the mechanism. Secured to the base of the external shaft and to the top of the internal shaft are friction clutches which correspond and fit into each other. When the shaft revolves the clutch permits a revolution a little greater than the normal one, but as the sides of the clutch are inclined the shaft immediately drops back into the proper position.