Patent GB-238954-A (GB)
Title: Improvements in and relating to power controlling mechanism for use in pneumatic despatch systems
IPC: B65G51/16
Filed: 1924-05-28
Abstract: 238,954. Lamson Pneumatic Tube Co., Ltd., and Cowley, J. T. May 28, 1924. Pneumatic dispatch apparatus.-In a control device for automatically applying power on the introduction of a carrier, and for rapidly shutting off the power where the carrier is ejected, the transmission tube is connected to a vacuum drum by a balanced valve which is controlled by pressure changes in the line acting on a flexible diaphragm, sensitive needle valve or an auxiliary diaphragm acting to shut off the drum on the discharge of the last carrier. Transmission tubes from the sub-stations discharge at a central station, continuations of the tubes passing through the station disc to the controlling device and vacuum drum. In the construction shown in Fig. 2, the line-pipe leads to a chamber 6 projecting transversely within a chamber 10 which is in constant communication with the vacuum pipe 8. Restricted communication between the chambers 6, 10 is normally maintained through a small port 17, full open communication being established between the vacuum and the line pipe when the piston-valve 15 is raised clear of the chamber 6. Guide-fins 16 centre the valve 15 in its open position. A bye-pass 115, Fig. 5, may take the place of the port 17, or the head and seating of the valve 15 may be made a loose fit. A hollow casing 24. above the chambers 6, 10, is divided by a flexible spring-loaded diaphragm 26, carried between plates 29, 30, the space 27 above the diaphragm communicating through a port 42 and passage 40 with the chamber 6, and the space below being always in communication with the atmosphere through a port 28. The central. part of the casing 24 is formed with an upstanding boss 32 screw-threaded for an adjustable gland 34, which guides a stem member 35 formed with a nut 36 to contact with a nut 31 on the main valve stem 19. The space 27 is formed with ports 43, 46 controlled by needle-valves 44, 48 respectively, the port 43 communicating with the passage 40, and the port 46 with the atmosphere. A lever 56, pivorally supported from the casing, is adapted to close either the port 42 or the port 46, being spring-actuated from the stem member 35 and normally closing the port 46. In operation, the placing of a carrier in the line causes an initial drop in line pressure communicated to the space 27, thereby raising the diaphragm 26 and the stem 35, and opening the main valve 15. The diaphragm 26 then rises, under the further pressure drop, to move the valve 15 to the fully open position, lifting the stem 35 until the spring snaps over the lever 56 to close the port 42 and open the port 46. The pressure in the space 27 is then kept steady, the inflow of air past the needle 48 balancing the leakage past the needle 44. On discharge of the carrier the line-pressure rises slightly, the leakage from the space 27 decreases, and the pressure rises to return the diaphragm 26 to its normal position and close the main valve. The stem 35, lagging slightly on the diaphragm, then falls, closing the port 46 and opening the port 42. Normal leakage from tho space 27 is compensated by a further needlevalve, not shown. In the modified device shown in Fig. 5, the actuation of the controlling valve 140 is effected by an auxiliary diaphragm 153, are spaces 156, 157 above and below the diaphragm, connecting with a balanced piston-valve 162 which also communicates through a pipe 166 with the vacuum chamber 112. A finger 171 on the main diaphragm stem member 147 engages a recessed piece 170 on the piston 162. In operation, when the main diaphragm rises, the finger 171 lifts the valve 162 to connect the space 156 with the pipe 166 between the valve-heads, and the diaphragm 153 rises, closing the valve 140. Owing to the lost motion in the extension 170, the main-valve closes before the piston 162 is restored to its normal position, thereby connecting the space 156 with the chamber 112 and opening the valve 140.