Patent GB-269452-A (GB)
Title: Improvements in or relating to mechanism for operating threeposition railway signals
IPC: B61L5/16
Filed: 1926-12-22
Abstract: 269,452. Underwood, W. J. Dec. 22, 1926. Visual outdoor signals.-The motor mechanism for operating three position railway signals is actuated by pressure fluid electrically controlled. The mechanism consists of cylinders 1, 2 the lower 1 being fixed while the upper 2 can oscillate about trunnions which contain the compressed air admission nozzle 12. The piston 4 of the cylinder 1 supports a pusher plate 6 which engages the roller 7 at the end of a crank arm 8 fixed upon the spectacle shaft 9. A second crank arm 11 fixed to the shaft 9 is connected to the end of the rod of the piston 13 in the cylinder 2. In the danger position, with the signal arm horizontal the parts are in the position shown in Fig. 1 and the piston 13 closes the admission nozzle 12. The admission of compressed air is controlled by the electromagnetically operated valves 19, 20 in connection with the track. When the valve 19 is operated the fluid is admitted to the cylinder 1 and the piston 4 rises to rotate the crank arm 8 thereby moving the signal arm from "danger" to "caution." The same operation also moves the cylinder 2 into a vertical position and moves the piston 13 away from the admission nozzle 12. The parts are then in the position shown in Fig. 3. The valve 20 can then be operated at the proper time to admit fluid to the cylinder 2 causing its piston to descend to operate the crank arm 11 and move the signal arm 10 from "caution" to "clear" as shown in Fig. 6. The proper sequence of operations is assured by the piston 13 closing the nozzle 12 in " danger " position and by the piston rod 14 being almost in line with the crank 11. On a following train entering the section protected by the signal the valves 19. 20 are deenergized and open the cylinders 1, 2 to the atmosphere so that the signal arm returns to the "danger" position. The movement of the arm to the "clear" position may be arranged to deenergize the valve 19. The cylinders 1, 2 may be arranged so that when cylinder 2 is in its operative position the two are at right-angles, as shown in Fig. 8. In another modification cylinders 21, 22, Fig. 10 are supported on hollow lugs 23, 24, so that both can oscillate. The piston rods are connected to a bar 29 attached by a pin 30 to the crank arm 11 on the spectacle shaft 9. The circuits for the operating coils of the valves 19, 20 include contact strips 35, 36, 43 which are traversed bv a contact bridge 33 attached bv a rod 34 to the bar 29. When the track conditions are right the valve 19 is energized through the conductors 39, 40 and the signal arm is moved to "caution." The bridge contact 33 is moved in this operation, to connect the strips 35, 36 to close the circuit for the coil of the valve 20 which is energized when the track conditions are right. The valves cannot, therefore, be operated in the wrong order. Instead of the rod 34 being attached to an electric contact device it may be attached to an arm on a plug valve arranged so that fluid cannot be supplied to the cylinder 22 until the signal arm is in the "caution" position. The apparatus may be combined with track relays to ensure automatic action.