Patent GB-707965-A (GB)
Title: Pneumatically operated gas flow control apparatus
IPC: C02F1/76
Filed: 1950-01-18
Abstract: 707,965. Proportionate mixing of fluids. WALLACE & TIERNAN CO., Inc. Jan 18, 1950 [Feb. 1, 1949], No. 1359/50. Class 86 [Also in Group XXIX] Apparatus for controlling the pressure of a gas flowing in a conduit comprises a regulating valve in the conduit, a pressure-responsive device sensitive to the pressure in the conduit adjacent the valve and controlling a powered driving device for adjusting the valve, resilient means responsive to the pressure-responsive device for reducing the adjustment of the valve when the change in conduit pressure is of only a temporary or transient nature, and delayed means responsive to continuing departure of the conduct pressure from normal for modifying the power supply to the driving device to effect continued adjustment of the valve to give complete restoration of the conduit pressure to normal. As applied to apparatus for dosing water with chlorine, the water flows along a conduit 12 past an adjustable valve member 17 situated in the throat of a venturi section in the conduit. The suction effect produced at the throat of the venturi sucks in the chlorine gas which flows from a supply pipe 10, past a control valve 74 into a chamber 28, past a restriction 30, along a conduit 32, and past a further control valve 140, and a non- return valve 36. Chamber 28, a further chamber 50, and. the passage 44 connecting the two chambers, constitute a U-tube, the lower part of which is filled with water. Chamber 50 is kept at atmospheric pressure by means of overflow pipe 54 which communicates with the outside adr through an aperture 61 leading into a sump 56, the latter having an outlet pipe 62 to the outside atmosphere, and the water level in the chamber is kept constant by supplying water continually through a pipe 51 and allowing the excess water to drain away to the sump through apertures 58 in the pipe 54. Any variation of the negative pressure in the gas in chamber 28 will cause a variation in the level of the water therein, and such change of level is detected by a float 80 and communicated through a U-shaped lever 82 pivoted at 83, a link 85 and a lever 88, to a valve 105 controlling a leak from a chamber 100. The resulting change in pressure in chamber 100 moves a diaphragm 106 in which the leak port is situated, and this movement is communicated through a yoke 90, rod 94, and a yoke 75, to vary the position of valve 74 and so tend to restore the pressure in chamber 28 to its pre-determined value. Lever 88 is pivoted to the yoke 90 and thus constitutes a floating lever giving an anti-hunting effect to the movements of valve 74, but this construction will cause float 80 to balance out in a different position after a correcting movement. To correct this, the pressure in chamber 100 is applied through a pipe 120 to the underside of coupled diaphragms 125, 127 actuating a valve 133 which controls the flow of compressed air from supply lines 287, 289, through lines 134, 102, past a restriction 103 to chamber 100. A restriction 121 in line 120 ensures that the correcting action takes place only on long period variations. To prevent overshooting, lever 88 is loaded by substantially-balanced springs 110, 115 of which spring 110 is adjustable. Valve 140 is controlled in accordance with the pressure downstream of metering orifice 30 by a controller 144 similar to the controller 92 for valve 74, but in this case the negative pressure in conduit 32 is applied through a line 151 to a chamber 150 containing a floating bell 160. Water is supplied to the chamber from a pipe 157 and the level is maintained constant by means of an overflow pipe 154 leading to the sump 56. Manometers 250 to 252 for indicating the degree of vacuum at various points in the apparatus are provided, each manometer consisting of an indicating limb which communicates at its lower end with a common water chamber 256. Water is supplied from a pipe 265 to manometer 252 from where it overflows into the chamber 256, and the level in that chamber is kept constant by means of an overflow pipe 257 leading to sump 56. Manometer 251 communicates with pipe 32 downstream of orifice and so indicates the pressure in that section and manometer 252 communicates with the inside of bell 160 and indicates the degree of vacuum there. Vacuum is applied to the underside of bell 160 from an aspirator 200 in an air-supply discharge line 201 connected to line 134, and this vacuum conduit 202 is provided with a valve 230 leaking-off to atmosphere by which the degree of vacuum can be adjusted. The valve in question is controlled by a diaphragm 223 subject to the negative pressure in a chamber 222 and to the tension of an adjustable spring 224, and the datum position of valve 140 is set by adjusting spring 224 from the hand-wheel 207. Manometer 250 indicates the degree of vacuum in chamber 28 and the pressure due to this column of water is applied to the underside of a diaphragm 304. If this pressure becomes excessive due to a failure of the vacuum, the diaphragm pushes up a lever 294 which is caused by its loading spring to fly past the dead-centre' position to contact and force a valve 283 on to its seat and so shut off the supply of compressed air to the controller 92. This will result in the shutting of valve 74. Specification 708,044, [Group XXIX], is referred to.