The present invention relates to bi-directional pneumatic conveyance systems, terminal stations therefor, and pressure generation elements therefor. More particularly, the present invention relates to a composite pneumatic conveyance system, a terminal station for use in such a pneumatic conveyance system, a pressure generation apparatus for such a terminal, and a controllable apparatus for carrying out airflow control for such a pressure generating apparatus.
Conventional commercial pneumatic tube conveyance or transportation systems have required two or more pumping elements in order to generate vacuum conditions and pressurization conditions within the pneumatic tube network. Vacuum or depressurization, and pressurization conditions, of course, are required in order to effect conveyance of a carrier to-be-transported between stations of the system. The cost and complexity of such transportation systems, depend in large part, upon the number of pump elements that are required for effective operation of the system. Accordingly, configuration of such a system to have only a single pumping element is desirable.
Also, conventional systems typically are controlled according to time. That is, in such a conventional system, when the carrier is first sent from a sending station to a receiving station, a clock mechanism deactivates the pumping elements for the system, and opens access doors at the receiving station after a predetermined time interval. The predetermined time interval is based upon the time that normally is required for the carrier to traverse the distance from the sending to the receiving stations. Such a timing control implementation is subject to problems where the system temporarily has been disabled as by a local power failure. In such conditions, the carrier could be left stranded anywhere in the tube network, and transport of the carrier therefore would not agree with the system's preset timing.
Examples of conventional elements for conventional by-directional pneumatic transportation systems are provided by various U.S. patents. For example, the assignee's U.S. Pat. No. 5,147,154 shows a pressure regulation device that includes a valve assembly which cooperates with an air dam in order to control pressure within a pneumatic tube system connected to such apparatus. The apparatus disclosed in this patent relies upon two pumping elements and the valve assembly and air dam in order to accomplish pressure regulation.
U.S. Pat. No. 4,971,481 specifically relates to a pneumatic carrier stop device. When the carrier passes over certain vents in the transport tube, the carrier redirects airflow in the system to facilitate capture of the carrier for operator removable. This patent is understood to show a carrier terminal that includes a single chamber housing which has a movable, multi-plunger device provided therein. The plunger is responsive to air flow directed into the housing. Control of airflow into the system depends upon the position of the carrier to the extent that the carrier blocks the vents in the system tubing to redirect pressurized air into the housing; this in turn determines the position of the multi-plunger. Various entrances and exhausts in the housing, and an airline connection between the housing and the upper portion of the transport tube are disclosed.
U.S. Pat. No. 1,586,634 relates to a control device for a pneumatic carrier delivery system. The control device is understood as a cylindrical housing having a movable plunger provided therein. The housing also includes a fixed partition and several vent structures. As a carrier traverses through the tubing of the system, the plunger adjusts to maintain proper pressure within the system.