Figure 1-36.-Dry-element air cleaner.demand for air is small. The dry air cleaner cleans theair by passing it through layers of cloth or felt thatremoves large dirt particles from the air very effectively.Dry-Element Air CleanersThe two most common dry-element air cleanersused are the cleaner with an unloading valve and acleaner with a dust cup (fig. 1-36).Dry air cleaners are built for two-stage cleaning:pre-cleaning and filtering. The cleaner with the dustunloading valve, as shown in figure 1-36, view A,directs the air into the pre-cleaner so that it strikes oneside of the metal shield. This starts the centrifugalsuction that continues until it reaches the far end of thecleaner housing. At this point, the dirt is collected intothe dust unloader valve located at the bottom of thehousing.The dust unloader valve is a rubber duck-bill devicethat is held closed by engine suction while the engine isrunning. When the engine is shut down, the weight ofthe accumulated dirt helps open the flaps so the dirt candrop out. The cleaner with the dust air cup, as shown infigure 1-36, view B, pulls in the air past tilted fins thatstarts the centrifugal suction. When the air reaches theend of the cleaner housing, the dirt passes through a slotin the top of the cleaner and enters the dust cup.Both types of pre-cleaners remove over 80 percentof the dirt particles, greatly reducing the load on thefilters. After the air goes through the pre-cleaning stage,it then passes through the holes in the metal jacketsurrounding the pleated-paper filter. Filtering isperformed as the air passes through the paper filter thatfilters out almost all of the remaining small particles.Checking and cleaning air cleaners equipped witheither a dust unloading valve or dust cup is part of thedaily prestart and post-operational checks andmaintenance performed by the operator. The dustunloading valve should be inspected for cracks,clogging, and deterioration. The dust cup should beremoved and wiped clean with a rag. Dusty filterelements should be removed and cleaned by tapping androtating the filter on the heel of your hand to remove thedust.NOTE: Do not tap the filter on a hard surface; thiscan damage the element.When the tapping does not remove the dust, use acompressed air cleaning gun to clean the filter(fig. 1-37). Direct the clean dry air up and down thepleats, blowing from inside to outside.NOTE: To prevent rupturing the filter, you must notallow the compressed air pressure to exceed 30 psi.To clean with water, you first blow out the dirt withcompressed air, then flush the remainder of the dirt frominside to outside with water. After flushing is completed,allow the filter to dry.1-26
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