Dust Control Handbook for Industrial Minerals Mining and Processing

Figure 1.24. Double dump weight-based valves.Tilt ValvesTilt valves are similar to double dump valves and are normally used in pairs. These valvescommonly have a near horizontal and counterweighted flap door that is adjustable for closedtension. The function of the valve is to allow material to build up on the near horizontal flap gateuntil it overcomes the pull of the negative pressure in the baghouse. The material then dumps tothe next valve as the gate shuts behind it. Typically a divider chute 24–30 inches long is usedbetween the two valves to allow one valve to close completely before the other opens.Tilt valves are less expensive than double dump and rotary valves, but can be hard to adjust.They have been known to stick open after being in service for a period of time, and they require4'0" clearance below the baghouse for installation.Vacuum or Dribble ValvesA vacuum valve basically consists of a soft gum rubber tube mounted in a steel housing, whichattaches to the bottom of a baghouse hopper discharge. Manufacturers have various designsavailable for purchase, some using a "fishtail" dribble bladder mounted inside a flanged pipe.The valve works using the negative pressure of the hopper to collapse the rubber tube and sealthe discharge until sufficient material builds up and "dribbles" through. This valve normally haslow initial cost, high reliability, and low maintenance, and can fit in a short discharge space.FILTER FABRICSThe majority of development work that has been done in the industry over the last ten years hasnot been in the area of the collector itself but in filter fabrics. Some of these fabrics have beendesigned to handle the more challenging applications. Problems that particular fabrics address44 Fundamentals of Dust Collection Systems