equipment. Hoses are manufactured in layers (fig.4-12). The inner layer is made of synthetic materialsthat resist deterioration from the fluid in the system. Themiddle layer or layers are made of either fabric or rubberfor low-pressure systems or wire braid for high-pressure applications. These layers give the hose itsstrength.Part of your pre- and post-operational inspections isto inspect hoses for cracking or splitting, pinhole leaks,improper hose length, rubbing, heat, twisting, and soforth. Any problems with hydraulic hoses should berepaired before use.QUICK-DISCONNECT COUPLERSQuick-disconnect couplers (fig. 4-13) are usedwhere hydraulic lines must be connected or dis-connected frequently;for example, in the NCF,quick-disconnect couplers used on front-end loadersFigure 4-12.—Hydraulic hose construction.allow quick changing of loader buckets, backhoes, andforklift attachments.The quick-disconnect couplers are self-sealingdevices that accomplish the work of two shutoff valvesand a tube coupler.They are easy to use and keephydraulic fluid loss at a minimum. More importantly,you do not have to drain or bleed the system each timea hookup is made.Quick-disconnect couplers consist of two halves:the body contains a spring-loaded poppet or seal, whilethe other half is inserted to open the poppet when thetwo halves are connected. A locking device holds thetwo halves and seals them.When quick-disconnect couplers are dis-connected on attachments, you must remember thatit is very important that dust plugs are inserted inthe coupler ports. If dust plugs are unavailable, acommon practice is to use a plastic bag to wrap thecouplers in for protection from foreign matter.CAUTIONHydraulic systems can create up to3,000 pounds of pressure per square inch andthe fluids may reach temperatures above 200°F.Wear protective gloves and use extreme carewhen disconnecting and reconnectingquick-disconnect couplers.ACCUMULATORSAccumulators are sometimes placed in a hydraulicsystem to absorb shock. These are frequently used onFigure 4-13.—Quick-disconnect couplers.4-11
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