GB993849A - Improvements relating to filters - Google Patents

Abstract

993,849. Filters. LEDWARD & BECKETT Ltd. June 27, 1962 [July 7, 1961], No. 24714/61. Heading BID. A filter includes a pair of screens arranged in the form of a V and mounted in a casing having inlet and outlet ports, so that the pair of screens can move between two positions in which the inlet port is on opposite sides of the apex of the V, while the outlet port communicates with the space between the limbs of the V in both positions. The screens may be arranged to move linearly in a casing of uniform cross-section, or preferably, arranged to turn about a pivot in a cylindrical casing. Thus, in one position, one screen is between outlet and inlet ports, while the other is between outlet port and a stagnant pocket. In the other position, the role of the screens is reversed. Preferably a flushing valve is provided in each of the stagnant pockets of the casing so that momentary opening of the appropriate valve to a low pressure region, e.g. a drain, causes a reverse flow through the inoperative screen and washes dirt therefrom. In one embodiment, Fig. 1, the screens and casing form a selfcleaning strainer box for use in e.g. a cooling water circulating system. The box comprises a casing 10 having inlet and outlet ports 14 and 15, provided with pipe connecting flanges 16 and 17. Within the casing, a frame comprising screens 18 and 19 is mounted on a pivot 22 so that the screens can be rocked between the two operative positions shown in Figs. 1 and 5. In one end plate of the casing, are mounted flushing valves comprising ports 26 and 27 covered by arcuate plates 28 and 29 connected to the frame that carries the screens. The extent of the plates is such that the ports are covered in both operative positions of the screens, but if the pair of screens is moved beyond one operative position, the flushing valve of the inoperative screen is opened, Fig. 6. Thus, with the screens in one operative position, Fig. 1, liquid flows through screen 19, which collects dirt on its outer surface. When the screen becomes clogged, the screens may be moved to and momentarily beyond the other operative position, Figs. 5 and 6, so that the screen 18 becomes operative and, due to the opening of the flushing valve, dirt is washed from screen 19 by reverse flow. The movement may be effected manually or automatically. In a preferred arrangement, a pressure drop across the strainer caused by clogging of a screen causes a pressure differential switch to actuate a motor connected via a cam and connecting rods to the central shaft 22 so that a change-over to the clean screen, and a momentary reverse flow through the dirty screen, are effected, leaving the latter screen in readiness for the next change-over.