baghouse; however, maintenance needs are somewhat greater. Pulse jet In reverse pulse-jet baghouses, individual bags are supported by a metal cage (filter cage), which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag. The pulse-jet baghouse was invented by MikroPul (currently part of the Nederman group and still a major supplier of filtration solutions) in the 1950s. Bags are cleaned by a short burst of compressed air injected through a common manifold over a row of bags. The compressed air is accelerated by a venturi nozzle mounted at the reverse-jet baghouse top of the bag. Since the duration of the compressed-air burst is short (about 0.1 seconds), it acts as a rapidly moving air bubble, traveling through the entire length of the bag and causing the bag surfaces to flex. This flexing of the bags breaks the dust cake, and the dislodged dust falls into a storage hopper below. Reverse pulse-jet dust collectors can be operated continuously and cleaned without interruption of flow because the burst of compressed air is very small compared with the total volume of dusty air through the collector. On account of this continuous-cleaning feature, reverse-jet dust collectors are usually not compartmentalized. The short cleaning cycle of reverse-jet collectors reduces recirculation and redeposit of dust. These collectors provide more complete cleaning and reconditioning of bags than shaker or reverse-air cleaning methods. Also, the continuous-cleaning feature allows them to operate at higher air-to-cloth ratios, so the space requirements are lower. A digital sequential timer turns on the solenoid valve at set intervals to inject air into the blow pipe and clean the filters. Cleaning considerations Sonic horns Some baghouses have ultrasonic horns installed to provide supplementary vibration to increase dust cleaning. The horns, which generate high intensity sound waves at the low end of the ultrasonic spectrum, are turned on just before or at the start of the cleaning cycle to help break the bonds between particles on the filter media surface and aid in dust removal. Rotating mechanical cage In addition to the most common of baghouse cleaning methods is a relatively new way to use the bag filter cage. The rotating mechanical cage option consists of a fixed cage attached to the cell plate. In addition to