Document ZnjNOnq9ZGy456zMQvpk9d5vp

EXHAUST SYSTEMS, GENERAL ir COMFORT VENTILATION STOCKING TYPE SCREEN RAPl MECHANISM RSE AIR FLOW SECTIONS 1,2 AND 3 UNDER AIR LOAD SECTION 4 CLOSED OFF FOR SCREEN CLEANINS MULTIPLE SECTION CONTINUOUS AUTOMATIC Fig 28-1T. Three type* of doth filters Courtesy American Conference of Industrial HyQienistt "Industrial Ventilation" stopped periodically, at which time the shaker comes on automatically for a vanable period, usually two to five minutes, and then shuts off Regular shaking is essen tial, and this is the best way to assure it A U-tube or water manometer should be permanently mounted on the outside of the casing, so the pressure drop can be checked at least daily A buildup of filter resist ance, as shown by mcreased pressure drop, is the warning sign that the filter is becom ing plugged and needs to be shaken Access doors should be located conveni ently so the intenor of the casing can be checked penodicaUy, perhaps weekly, for leaks m die bags, bridging of dust u the hopper, etc Too often filters are located where they are inaccessible--and are then neglected Cloth filters of the "reverse air )et" type that can be continuously cleaned during fil tration (no shutdown) are widely used (see Fig 28-12) They consist of a felt-like tube with the dusty air entering on the in side On the outside is a slotted nng made of pipe that continuously travels up and down the bag surface. Compressed air is blown at high velocity out the slot, which in passing through the bag dislodges the dust, so it falls down in the dust hopper The rate of air flow delivered by the ex haust system may be 15 to 40 cfm per square foot of cloth, far higher than in the 28-23