Patent GB-618228-A (GB)
Title: Flow control apparatus
IPC: G01F1/22
Filed: 1945-03-20
Abstract: 618,228. Fluid-pressure servomotor-control systems. FISCHER & PORTER CO. March 20, 1945, No. 7022. Convention date, May 3, 1944. [Class 135] Apparatus for controlling a variable condition, such as fluid flow, comprises an airoperated valve under the control of a tiltably mounted flapper which varies the escape of compressed air from a restrictive rozzle in accordance with changes in the variable condition, the action of the flapper being adjustably throttled by a rotatably mounted bellows assembly, the lateral movements of which counteract the tilting of the flapper, and the throttling action being adjusted by rotation of the bellows assembly to vary the lateral com. ponent of bellows movement. Fig. 1 shows the complete control system, which includes an air-operated valve 49 in a pipe 21 conteuning a flow-meter 20 of the kind described in Specification 610,708, [Group XXXV], and a control unit 30 which responds to the movements of the flow-meter and controls the air pressure applied. through a conduit 90 to the valve 49. Pressure air is supplied to the unit 30 through a pipe 51 containing a filter 52 and a reducing valve 53. The valve and flowmeter may be byepassed by pipes 130, 129, respectively for replacement or repair. The flow-meter comprises a floating disc 23, Fig. 3, moving in a glass tube 22 and carrying an armature 25 adapted to move from a central position to unbalance an impedance bridge comprising aligned transmitter coils 26, 27 and parallel receiver coils 28, 29 with armatures 32, 33, located in the unit 30 and connected to a balance beam 31. The beam 31 is connected by a linkage 109, 110, Fig. 2, to a pen arm 106 moving over a chart 111, Fig. 1, driven by a motor 112. The pivot 107 of the pen arm also bears a pointer 35 connected by gears 36, 37 to a lever 38 adjustable by a knurled wheel 105 on a screwed spindle 42. A floating lever 39 is connected to the lever 38 at 40 and to the beam 31 and to a double bell-crank 45 by links 41, 43, respectively. The bell-crank 45 has a fixed pivot 46 and carries a pin 47. The link 43 may be connected either at 44 or 50 to the bell-crank, depending on whether the valve 49 is urged to close or open by its loading spring. The pin 47 engages a floating lever 77 having a counterweight 80, Fig. 7, and a pivot 79 on the centre block 104 of a rotatable bellows assembly, Fig. 4. The lever 77 carries a U-shaped member 76 embracing a bail 78 on the back of the flapper 72. The latter is pivoted on a bracket 74 and has a counterweight 75 which keeps the lever 77 against the pin 47. The flapper 72 co-operates with a nozzle 69 which is supplied with air through a restricted conduit 67 from the lower diaphragm chamber 65 of a relay valve assembly 60. The chamber 65 is supplied with air through a capillary tube 62 in a fitting 61 connected to the air supply pipe 51 via a pipe 58 and a tee-joint 56. The diaphragm 63 carries a piston valve 81 controlling an exhaust port 124 and having an extension 84 which unseats a ball valve 83 on upward movement of the diaphragm. The ball valve 83 is supplied from the pressure supply pipe 51 through the tee 56 and conduits 57, 59. The chamber 82 between the valves 81, 83 is connected with the main valve 49 through conduits 86, 88, 90. Pressure gauges 55, 89 show the pressures in pipes 51, 90 respectively. The fitting 61 may be directly connected with the conduit 88 through a change-over valve 66, when manual operation of the valve 49 is required. The valve 66 connects the conduits 86, 88 during automatic operation. The upper diaphragm chamber 64 responds to the pressure in the control conduit 86 to which it is connected by a passage 91. The control conduit 86 is also connected by a conduit 93 and passages 99, 100, Fig. 4, with the left-hand bellows 94 of a bellows assembly comprising two opposed bellows 94, 118 mounted in a frame 95 fixed to a spindle 96 rotatable in a bearing 97. The bellows are joined by the centre block 104 which carries the lever pivot 79. The interior of the bellows 118 is likewise connected with the control conduit through passages 119, 120 and conduits 114, 117, but in this case an adjustable needle valve 115 and a receiver 116 of relatively' large volume are interposed in the connection so that pressure changes in the control conduit are effective in the bellows 94 much quicker than in the bellows 118. The lateral component of the movement of the centre block 104 only is effective on the operation of the flapper and this can be adjusted by bodily rotating the bellows assembly in the bearing 97. For this purpose, the spindle 96 carries a gear 98 meshing with teeth on the lower end of a vertical bar 125 also having teeth on its upper end meshing with a pinion 126. The pinion can be moved through 180 degrees by an arm 127 and in so doing causes the bellows assembly to move through 90 degrees. In the horizontal position of the bellows assembly, its damping action is the greatest and the sensitivity of the control is least. When the bellows are vertical, the sensitivity is greatest and the damping effect is nil. In operation, a decrease in flow causes the floating disc 23 to fall and this unbalances the impedance bridge and causes the beam 31 and therefore the bell-crank 45 to rotate clockwise. This moves the flapper towards the nozzle 69 so that pressure rises in the lower diaphragm chamber 65 and the ball valve 83 opens the conduit 59. Pressure therefore rises in the control conduit 86, 88, 90, and so the valve 49 tends to open against its spring and therefore restore the flow to normal. The rise in pressure in the control conduit also acts above the diaphragm 63 which therefore descends, allowing the ball valve 83 to close. The rise in control pressure also acts inside the bellows 94 and through the floating lever 77 tends to move the flapper 72 away from the nozzle 69 back to its original position but does not completely do so. The damping action which the bellows 94 has on the control would result in the latter drifting from the control point were it not for the bellows 118. The rise in control pressure acts with an adjustable delay in the bellows 118, which acts on the flapper in opposition to the bellows 94. An increase in flow in the pipe 21 acts on the control in a similar but contrary sense. The control point may be adjusted by the wheel 105, the change being indicated by the pointer 35, whilst the damping action and the sensitivity of the control are adjustable by the arm 127.