Shaker bags are used in an older concept dust collector design which goes back several decades before the introduction of pulse jets. In the shaker concept, the filter bag collects dust on the inside surface. The typical shaker collector is compartmentalized so that a single compartment can be taken off-line for cleaning. After closing the dampers, the bags in the off-line compartment are mechanically shaken by the bag hanging system in the top of the compartment. In all cases, the bag is physically agitated in order to dislodge the dust. As the filter bags are shaken down, the dust drops down into the hopper below to be removed by airlock, screw conveyer or slide gate.
Shaker bags may be clamped over a thimble or snapped into a hole at the bottom tube sheet area and then hung by strap, hook or loop at the top to suspend the bag and to have a positive attachment method during a vigorous shake down. After shake down and settling of the dust, the off-line compartment is put back on line as the next compartment is taken off-line to begin its cleaning process. Bag cleaning may happen several times a day or less frequently depending on dust load and the size of the collector.
Originally shaker bags were all made from woven fabrics. Special weave patterns were used to optimize fabric shift and movement during the shakedown in order to facilitate dust release. Today, lightweight felts are specially designed as shaker felts and may be used in shaker collectors either with the existing mechanical shaker system or in conjunction with sonic horns. Sonic horn cleaning, in most cases, is as effective as or more effective than mechanical shakers. As an added benefit, sonic horns may allow the complicated shaker system to be deactivated, providing a significant maintenance parts and labor savings.
Shaker bags can be made from fabrics in all fiber groups from cotton to polyester to PTFE and in a range of designs from smooth multifilament fabrics to heavy spun fabrics to shaker felts. Each material or design meets a specific process or environmental need. Most shaker collectors operate at relatively low air to cloth ratios, meaning that a larger collector has to be built to handle the same air volume as a pulse jet. The metal industry in general has been the biggest industry segment using and continuing to use the shaker dust collector concept.