Pneumatic conveyor systems
BACKGROUND OF THE INVENTION 
     The present invention concerns a pneumatic conveyor system. 
     In a pneumatic conveyor system objects are transported to and from stations along ducts and it is desirable to achieve a smooth arrival of docking of objects at the stations. 
     FEATURES AND ASPECTS OF THE INVENTION 
     According to the present invention a pneumatic conveyor system comprises a main duct for the transport of objects to and from a docking unit, a branch unit from the main duct communicating with a first port in a valve body, the valve body having three further ports communicating respectively with an exhauster, the docking unit and atmosphere, and a rotatable valve member in the body capable of providing communication between any two adjacent ports and isolating the other two ports. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be described further, by way of example, with reference to the accompanying drawings; in which: 
     FIG. 1 is a schematic diagram of a portion of a pneumatic conveyor system; 
     FIGS. 2a to 2d inclusive depict a valve used in the conveyor system of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic diagram of a portion of a pneumatic conveyor system in which objects are propelled pneumatically along a duct 1 to and from a sampling station 2. For example, the objects can be carriers each containing a sample bottle which can be transported between a control station, such as a laboratory and the sampling station. A docking unit 3 for carriers is provided at the sampling station 2 and it is required to control the arrival of the carriers at the docking unit. 
     The carriers are propelled pneumatically along the duct 1 by creating a pressure drop (suction) ahead of the carrier in the direction of travel. Thus, at the sampling station end of the conveyor system an exhauster (suction pump) communicates with the duct 1 by way of a control valve 4 located in a branch duct 5. As shown in FIGS. 2a to 2d, the valve 4 comprises a cylindrical valve member 6 rotatable within a valve body 7 having ports 8, 9, 10 and 11. Ports 8 and 9 communicate with the branch duct 5, port 10 leads to the exhauster (not shown) and port 11 is open to atmosphere. The valve member 6 is shaped as shown to provide an unobstructed flow path between any two adjacent ports. 
     Initially, to receive a carrier at the docking unit 3 the valve member 6 is set in the position shown in FIG. 2a. In this position the valve member allows communication between the exhauster and the duct 1 and blanks off the ports 9 and 11. A first proximity switch is provided to indicate this position of the valve member 6. The suction applied by the exhauster to the duct 1 draws a carrier along the duct to the junction of the duct 1 with the duct 5. On arrival at the junction the carrier trips a switch to energise a motor for the valve member 6 whereby to rotate the valve member 6 through 90°. FIG. 2b indicates the valve member during rotation and with the exhauster port 10 communicating with the ports 8 and 9 with the port 11 remaining blanked off. The rotation of the valve member 6 through 90° can take approximately 15 seconds and during this rotation the pressure balance on the carrier reaches a value sufficient to draw the carrier slowly and smoothly into the docking unit 3. When the carrier arrives at the docking unit it triggers a switch which provides a signal to switch off the exhauster. The valve member 6 completes its 90° rotation which is signalled by a second proximity switch and then proceeds to rotate through a further 90° to reach the position shown in FIG. 2c. Should the second proximity switch be activated before the arrival of the carrier at the docking unit then this would be an indication of a fault condition. With the valve member in the position shown in FIG. 2c the duct 1 is isolated from the exhauster. The same exhauster can be employed to transport carriers to a number of sampling stations. 
     In position FIG. 2c the air inlet port 11 communicates with the docking unit 3 and the duct 1. Operation of a further exhauster at the opposite end of the system draws the carrier out of the docking unit 3 to return along the duct 1. As the carrier passes the T-junction of the duct 5 with the duct 1 it again activates the switch at the junction to signal the valve member 6 to rotate into the position of FIG. 2d. In this position the duct 5 communicates with the port 11 to permit unrestricted venting of the duct 1. The valve can remain in the position of FIG. 2d until it is required to despatch a further carrier to the sampling station.