Patent GB-1102150-A (GB)
Title: Fluid strainer
IPC: B01D29/00
Filed: 1965-11-26
Abstract: 1,102,150. Filter with electrical fluid flow control. CARRIER CORPORATION. 26 Nov., 1965 [21 Dec., 1964], No. 50444/65. Heading B1D. Filtering apparatus for filtering a continously flowing stream of fluid involving backflushing by filtered liquid comprises a body member 10 with an inlet in cover 18 and an outlet in cover 20, two filtering chambers 14, 16 arranged for alternate parallel filtration, perforate cylindrical filter elements 38 in each chamber, valve means 26 positionable for selectively directing fluid flow through one of said chambers, drain means 62 or 64 allowing when open backflushing of filtered liquid through the filter element not performing filtration, and control means including cycle relays regulating electrical circuits controlling the position of valve means 26 and the opening of drain means 62 or 64 whereby the fluid flowpath may be changed to pass through the other filtering chamber and not through the first filtering chamber, and the backflushing action controlled over a predetermined time interval. The cycle relays may be selectively responsive to a combination of the position of the valve means 26 and hence switch 74, and either a pressure switch 52 (Fig. 2 and 3) responsive to a certain pressure differential between the inlet and outlet or a timer controlled switch 105 (Fig. 4, not shown). Switch means may be associated with each cycle relay for completing a holding circuit throughout said cycle relay for a predetermined time in the event of a change in either the valve position or pressure differential across the apparatus, said switch means being effective to prevent energization of the cycle relay other than the one associated therewith. Movement of valve means 26 is effected by compressed air from conduits 34 or 36 acting on piston head 33, which movement also causes flange 29 to change the position of switch 74 by engagement therewith. Opening and closing of drain valves 66, 68 is effected by compressed air. Perforated filter elements 38 comprise inlet openings (46) in their sides and may be withdrawn from the filter chamber after removal of the top covers (19). In use, with the valve means 26 in position as shown in Fig. 2 and with filtering flow through chamber 16 and backflushing through the filter element in chamber 14 having occured by the opening and closing of drain valve 66, and with switch 74 in the position as shown in Fig. 3, a certain pressure differential across switch 52 caused by clogging of the filter element 38 causes the switch 52 to close. This completes a circuit through normally closed switch 76, normally closed switch 78 and the solenoid controlling valve 58 to cause compressed air to be delivered through line 50 and conduit 34 to move piston 33 and valve member 26 to the left to stop liquid flow to chamber 16, allow fluid flow to chamber 14 and change the position of switch 74 (dotted line). At the same time, cycle control relay 70 is energised causing closure of contacts 79 of time delay switch 80 (e.g. with 10 seconds delay) to maintain activation of the solenoid controlling valve 58 and hence maintain flow of air through conduit 34 when switch 74 changes position and to provide a holding circuit through relay 70, also causing switch 82 to open to prevent energizing of cycle relay 72, and causing switch 84 to close to energize relay 86 which closes contacts 85 of time delay switch 88 (e.g. with 60 seconds delay.) Relay 86 also opens switch 86' and closes switch 90, thus energizing coil 87 to open valve 68 to permit backflushing through filter element 38 in chamber 16 and pipe 64. During backflushing the filter element in chamber 16 will be unclogged, the pressure differential across switch 52 will drop thus opening switch 52, cycle control relay 70 will be de-energized by opening of contact 81 of time delay switch 80, and then relay 86 will be de-energized by the opening of contacts 85 to open switch 90, deactivate relay 87, close valve 68 and thus terminate backflushing through conduit 64. When filter element 38 in chamber 14 becomes clogged, movement of valve means 26 and backflushing by opening of valve 66 is effected similarly involving relays 72 and 98, and time delay switches 94 and 100.