GB968826A - Improvements in and relating to liquid level differential sensing devices - Google Patents

Abstract

968, 826. Liquid level detectors; pressure responsive devices. FMC CORPORATION. Aug. 26, 1963 [Sept. 7, 1962], No. 33762/63. Headings G1H and G1L. A liquid level differential sensing device comprises two open-ended conduits 11, 12 inserted in different portions of a body of liquid, means associated with each conduit for supplying pressurised gas to the conduit to force bubbles of gas out of the immersed end of the conduit, and means 24 sensitive to the difference between the pressures in the conduits. The device is illustrated as being applied to a flowing stream of sewage or other liquid containing solids, the stream passing through a screen fitted with a comminuting device 13, preferably a rotary cutter which moves across the screen to clear collected solids. The comminuting device is arranged to be operated automatically when the solids collected by the screen cause the liquid level upstream from the screen to rise a predetermined height from the level downstream from the screen. The conduits 11,12 are arranged upstream and downstream respectively from the screen, and each conduit is supplied with air from a separate pump (only one, 23, shown in Fig. 2) the output of which is adjustable. Flexible conduit sections 20, 21 lead to the conduits 11, 12 from the pumps through tee-fittings 41, 44 which also lead to the pressure sensing means 24. This means, Fig. 3, comprises two chambers 30, 31 divided by a flexible diaphragm. A normally open micro-switch 36 is fitted inside the chamber 30 and this has an operating plunger 47 adapted to be actuated by a screw 33 carried by the diaphragm 29. The diaphragm also carries a U-shaped bracket 35 to actuate a reset button 48 on the switch 36. The conduit 11 is connected to the chamber 31 and the conduit 12 to the chamber 30 so that as the liquid level rises upstream from the screen the pressure to force air out of the conduit 11 rises and this rise moves the diaphragm 29 to close the switch 36 and start the comminuting device 13 when the liquid level differential reaches a certain value. As the comminuting device clears the screen the pressure differential in the chambers 30, 31 is reduced and the switch 36 is reset switching off the device 13.