Patent GB-238955-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: 238,955. Lamson Pneumatic Tube Co., Ltd., and Cowley, J. T. May 28, 1924. Pneumatic dispatch apparatus.-In a control device for quickly applying power on th introduction of a carrier, and for rapidly shutting off the power when 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, an auxiliary diaphragm acting to shut off the drum rapidly on the discharge of the last carrier. In the construction shown in Fig. 1, the line pipe 6 leads to a chamber 5 fitted within a chamber 2 which is in constant communication with the vacuum pipe 3. Restricted communication between the pipes 6, 3 is normally maintained through a bye-pass 7, full-open communication between the vacuum and the line-pipe being established when the piston-valve 8 is raised clear of the chamber 5. A hollow casing 31 above the. chambers 2, 5 is divided by a spring-loaded diaphragm 16, the space 25 above the diaphragm communicating through a passage 38 with the chamber 5 and the space 26 below communicating through a solenoid-controlled valve 34 with the atmosphere. A bleed-hole 27 is provided for the space 26. The diaphragm 16 is carried between plates 23, 24 secured to a bolt 21 on the stem 17 of the valve 8, the bolt having passages 28, 29 open to the space 25, and side-ports 30. The lifting of the valve 8 actuates a latch 60 and a pivoted contact arm 65 to close the solenoid circuit through contacts 70, 74. A spring-controlled bell crank lever pivoted through a lever 45 to a diaphragm 42, open to the space 25, maintains the solenoid-circuit after the piece 60 has passed the arm 65, the arm 51, which normally holds the contacts 70, 74 apart, being retracted by the movement of the diaphragm 42. In operation, the placing of a carrier in the line causes an initial drop in the line pressure and the diaphragm 16 rises slightly, carrying the latch 60 against the cam shoulder 67 of the arm 65 to establish the solenoid circuit. The solenoid 36 opens the valve 34, air enters the space 26 and the diaphragm 16 rises, thereby fully opening the main valve 8. The vacuum drum then exhausts the space 25, and before the diaphragm 16 approaches its upper limit causing the latch 60 to pass cut of contact with the lever 65, the diaphragm 42 descends, and the resisient contact arm 73 follows the bell-crank arm 51 to maintain the solenoid circuit. On delivery of the carrier, the line-pressure rises slightly, the spring-controlled diaphragm 42 returns to its normal position, thereby breaking the solenoid circuit and closing the valve 34. Air then passes from the space 25 to the space 26 through the ports 30 and passages 28, 29 in the bolt 21 and the valve 8 closes, the bleed-hole 27 completing the return to normal pressures. A bleed-hole to the vacuum pipe 3 may be formed in the valve 8, the byepass 7 being then omitted. A modified solenoidcircuit is shown in Fig. 5. A projection on the valve stem 17 swings an arm 168 to contact with a piece 169 when the valve 8 lifts, establishing the main solenoid-circuit. As the line-pressure falls an auxiliary spring-loaded diaphragm closes the contacts 156, 157 in a shunt solenoid-cricuit, an insulated finger, raised by a projection on the valve-stem 17, separating contacts 161, 162 and breaking the main circuit. As the line pressure increases when the carrier is discharged, the auxiliary diaphragm returns to its normal position, breaking the shunt circuit, and the solenoid valve closes. In this modification, a gravitycontrolled valve, connected to the underside of the main diaphragm, and is fitted over a port in the casing. A modified device comprises a needle valve connection between the chambers 25, 26, the solenoid-circuit being established by the lifting of the auxiliary diaphragm, the space above the diaphragm communicating with the line, the space below bleeding to the atmosphere. A control-diaphragm actuated similarly to the auxiliary diaphragm, is lifted by the pressure drop when the main valve opens, thereby breaking the main solenoid-circuit, and closing a second circuit to maintain the solenoid valve open, as in the lastmentioned modification. On discharge of the carrier, the line-pressure rises slightly and breaks the circuit to close the solenoid valve.