GB832728A - Improvements in or relating to the straining of liquids - Google Patents

Abstract

832,728. Filters. AMES CROSTA MILLS & CO. Ltd., and BOLTON, J. F. Sept. 25, 1958 [Oct. 8, 1957], No. 31387/57. Class 46. A filter screen 11 is an open channel 12 comprises curved bars 10 forming a part-cylindrical surface which are periodically scraped by a rake 18 which rotates about an axis 14, coincident with the axis of the screen, during its normal operative or upward stroke and the rake is retracted from the screen during its inoperative or downward stroke. In the form shown the rake 18 is carried by two telescopic arms 16, connected by a structure 25, fixed to a tube 15 rotatable about the axis 14. The tube 15 carries two arms 22 connected to hydraulic rams 19 which provide the rotational movement and a ram 28 is connected to the mid-point of spindle 15 and the structure 25, actuation of the ram 28 providing, through the telescopic arms, the retraction and reinsertion of the rake from the screen 11. In an alternative arrangement in Figs. 4-6 (not shown), the arms are rigid and the retraction of the rake is provided by a ram which moves the pivoted axis of the rake. In operation, with the rake in the position shown, the rams 19 move the rake upwards to clean the screen the rake passes a pivoted shoot 30 and is engaged by a pivoted scraper 32, the ram 28 is then actuated to retract the rake and the screenings are scraped off by the scraper 32 and fall into the shoot 30 to a channel or conveyer 34. The rake is then moved downwards by the rams 19 to its bottom position where the ram 28 is actuated to reinsert the rake into the screen. The inoperative position of the rake is in its upward retracted position clear of the channel. A lost motion connection is provided between the arms 22 and the rams 19 and relief devices are provided in the hydraulic circuit to allow for certain conditions. If a blockage such as a piece of wood becomes lodged at the bottom of the screen the rake is held retracted until the rams 19 raise the screen above this blockage when the rake is reinserted. Further if the blockage occurs further up the screen the rake on meeting the obstruction is retracted until it moves past the blockage when the rake is reinserted. If a large quantity of screenings collect during the inoperative time of the use of the rake, the rake on moving downwards penetrates these screenings to a certain extent and is then prevented from completing its downward stroke. The lost motion connection allows the rams 19 to complete their downward stroke and the rams 28 then reinserts the rake and part of the screenings are removed. Subsequent strokes of the rake gradually clear all the accumulator screenings.