HYDRAULIC FLUIDOn equipment, hydraulic fluids are used forhydraulic systems that steer, lift, push, close, and soforth. Hydraulic fluids that are currently in use includemineral oil, vegetable oil, water, phosphate ester,ethylene glycol compounds, and oil in water. The threemost common types of hydraulic fluids are water base,petroleum base, and synthetic base.NOTE: Before adding hydraulic fluid in a piece ofequipment, consult the operator’s manual for the type ofhydraulic fluid required. Using the incorrect type cancontaminate the hydraulic system which requires thatthe system be drained, flushed, and refilled with thecorrect fluid.NOTE: Before adding gear oil, consult theoperator’s manual for the type of oil required for thespecific type of equipment. Mixing different types ofgear oil may cause the oil to break down and not havethe quality required to protect the gears.Figure 1-42.-Filter system configurations.Filtering SystemsGEAR OILGear oils are used in both manual transmissions anddifferentials. Gear oils reduce friction and do not breakdown or foam at high temperatures.Two filter system configurations are in use today:the full-flow system and the bypass system.FULL-FLOW SYSTEM.— All the oil in the full-flow system (fig. 1-42, view A) is circulated through thefilter before it reaches the engine. When this system isused, it is necessary to incorporate a bypass valve in theoil filter. This valve allows the oil to circulate throughthe system without passing through the element in theevent that it becomes clogged. This factor prevents theoil supply from being cut off from the engine.BYPASS SYSTEM.— The bypass system (fig. 1-42,view B) diverts only a small quantity of the oil each timeit is circulated and returns it directly to the oil pan afterit is filtered. This type of system does not filter the oilbefore it is sent to the engine.GREASEGrease is used to lubricate bearings, bushings, andpivot points. For inaccessible bearings, grease is appliedunder pressure by the use of a grease gun (fig. 1-43).Figure 1-43.-Hand-operated grease gun.1-31
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