Dry-Element Air Cleaners

The two most common dry-element air cleaners used are the cleaner with an unloading valve and a cleaner with a dust cup (fig. 1-36).

Dry air cleaners are built for two-stage cleaning: pre-cleaning and filtering. The cleaner with the dust unloading valve, as shown in figure 1-36, view A, directs the air into the pre-cleaner so that it strikes one side of the metal shield. This starts the centrifugal suction that continues until it reaches the far end of the cleaner housing. At this point, the dirt is collected into the dust unloader valve located at the bottom of the housing.

The dust unloader valve is a rubber duck-bill device that is held closed by engine suction while the engine is running. When the engine is shut down, the weight of the accumulated dirt helps open the flaps so the dirt can drop out. The cleaner with the dust air cup, as shown in figure 1-36, view B, pulls in the air past tilted fins that starts the centrifugal suction. When the air reaches the end of the cleaner housing, the dirt passes through a slot in the top of the cleaner and enters the dust cup.

Both types of pre-cleaners remove over 80 percent of the dirt particles, greatly reducing the load on the filters. After the air goes through the pre-cleaning stage, it then passes through the holes in the metal jacket surrounding the pleated-paper filter. Filtering is performed as the air passes through the paper filter that filters out almost all of the remaining small particles.

Checking and cleaning air cleaners equipped with either a dust unloading valve or dust cup is part of the daily prestart and post-operational checks and maintenance performed by the operator. The dust unloading valve should be inspected for cracks, clogging, and deterioration. The dust cup should be removed and wiped clean with a rag. Dusty filter elements should be removed and cleaned by tapping and rotating the filter on the heel of your hand to remove the dust.

NOTE: Do not tap the filter on a hard surface; this can damage the element.

When the tapping does not remove the dust, use a compressed air cleaning gun to clean the filter (fig. 1-37). Direct the clean dry air up and down the pleats, blowing from inside to outside.

NOTE: To prevent rupturing the filter, you must not allow the compressed air pressure to exceed 30 psi.

To clean with water, you first blow out the dirt with compressed air, then flush the remainder of the dirt from inside to outside with water. After flushing is completed, allow the filter to dry.

Figure 1-37.-Dry filter cleaning.

For extremely oily filters, clean the filters with the compressed air or flush them with clean water. Soak and gently agitate the filter in a filter cleaning solution and lukewarm water. Rinse the filter thoroughly with clean water and then shake the excess water from the filter and allow it to airdry. Protect the filter from freezing, and keep a spare element to use while the washed one is drying.

After the filter is clean, inspect it for damage and check the filter gasket for damage. Before installing the filter, you must clean the inside of the air cleaner body thoroughly with a clean, damp rag.

NOTE: Consult the maintenance supervisor for approval before washing any filter elements with water. Additionally, never wash a dry element in fuel oil,

Figure 1-39.-Typical engine lubrication system.

gasoline, or solvent and never use compressed air to dry the element.

Oil Bath Air Cleaners

Oil bath air cleaners (fig. 1-38) draw air down a center tube where it strikes the surface of oil in the oil reservoir. As the air strikes the oil reservoir, most of the particles in the air do not make the 180-degree-upward turn. The dirt particles remain trapped in the oil. As the air continues upward and passes to the filter element, the smaller particles that bypassed the oil are trapped. The air keeps the filter element soaked with oil by creating a fine spray as it passes the reservoir. The air then makes another 180-degree turn and enters the intake system of the engine.

NOTE: It is the operator's responsibility to keep the oil cup filled to the proper level with the correct weight of oil and to document when the oil is dirty or has thickened, reducing its ability to clean particles from the air.

LUBRICATION SYSTEM

The engine lubrication system (fig. 1-39) reduces friction between moving parts, absorbs and dissipates heat, seals the piston rings and cylinder walls, cleans and flushes moving parts, and helps deaden the noise of the engine.

Checking the lubrication oils on a piece of equipment is part of the prestart check and the operator's responsibility. Also, it is a good professional practice to recheck the lube oil levels after a lunch break or during a crew turnover. The effort to check the lube oils is easier than explaining to the chain of command why an engine or part of the power train locked up or seized.

ENGINE OIL

Besides reducing friction and wear, engine oil acts as a cooling agent by absorbing heat from the surfaces over which it is spread. Engine oil carries heat to the engine sump where it is dissipated. The water circulating through an oil cooler also helps to reduce this heat (not all engines have oil coolers).

Engine oil is also used as a sealing agent. It fills the tiny openings between moving parts and cushions them against damage and distortion from extreme heat. Engine oil is very important as a cleaning agent. Grit and dirt in engine parts are often removed by the oil before damage can result. The foreign matter and the greases in the bottom of the crankcase are evidence that engine oil cleans. Some oils have chemicals, known as additives, added to make them even better cleaners.