Patent GB-1394248-A (GB)
Title: Pneumatic control device suitable for air filter cleaning apparatus
IPC: B01D37/04
Filed: 1972-07-14
Abstract: 1394248 Pneumatic motors; pneumatic control circuits BUEHLER AG Gebr 14 July 1972 [20 July 1971] 33028/72 Headings F1M and F1P [Also in Division B1] A pneumatic control device for sequentially venting to atmosphere a number of ports which are normally pressurized comprises a rotating venting arm with an associated venting valve driven by means of a compressed air engine and controlled by a pneumatic circuit involving one or more fluid logic elements. In the embodiment of Fig. 1, a plurality of ports 6 which are to be sequentially vented are arranged in a circle in the base of a cylindrical housing 4 containing a rotary venting arm 8 for sequentially engagement of each port 6, the remaining ports still being pressured by compressed air admitted at 53. The ports are vented to atmosphere via a passage 9 in the venting arm which may be closed by diaphragm 15 on the application of compressed air to the far side 17 thereof. The arm 9 is rotated by means of a cam 35 on reciprocating arm 23 driven by flexible diaphragm 20 and engaging a ratchet 35 mounted on the arm during the outward stroke of the arm 23. The arm is reciprocated by the application of compressed air to piston chamber 21 to one side of diaphragm 20, air being vented from this chamber by passage 28 which may be closed by a diaphragm 32 in a similar manner to passage 20. The far end of the piston-rod carries a plate 38 which alternately interrupts air-flow across gaps at 39 and 40 at each end of the pistons travel. A bi-stable logic element 41 is provided to control cyclic operation of the system. In the position shown in the figure, a port 6 has just been vented. Plate 38 is interrupting air-flow at 40. As a result of this input x2 of element 41 is zero whilst input xl is positive and the preferred output is y1 such that air is emitted therefrom to close membrane valves 15 and 30. Air-pressure, thus builds up in chamber 21 forcing the piston to the right whereupon air-gap 39 becomes interrupted rather than gap 40 and input x2 becomes positive whilst input x1 becomes zero. The element output changes to y2 and valves 15 and 30 are vented. Air escapes from piston chamber 21 and the piston completes a return stroke. At the same time the port 6 is vented via passage 9. The device is now ready to complete another cycle. The embodiment of Fig. 4 operates in a similar manner except that a centering device 115 mounted on a second piston arm 114 is provided to hold the venting arm 86 in exact engagement with the port 6 at each venting position. Each venting cycle is in this embodiment, initiated by attainment of a predetermined pressure differential in the device, e.g. filter device, to which the ports 6 are connected. The operation of this circuit involves the use of five fluid logic elements. An AND element 120 is fed by the initiating pressure measuring device 60 and OR-NOR element 119. When the piston 93 is at the left hand end of its movement interrupter valve 102 ensures no input to input x of element 119 which switches its output to y2. This has already one input fed by the outside pressure and triggers output y changing the output of bi-stable 121 to y1. Air flows along line 125 and the piston is pushed to the right whereupon valve 102 is opened and valve 103 closed. This causes operation of second OR-NOR element 123, reversal of output of element 121 and hence the return stroke of the piston and, at the same time, reversal of output at second bi-stable element 122 to vent the port valve 73 and operate the centering device 115.