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Figure 4-11.(A) Single- and (B) double-acting hydraulic cylinders.
Hydraulic Motors

Equipment Operator Basic - Beginning construction equipment operators manual
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equipment.  Hoses  are  manufactured  in  layers  (fig. 4-12). The inner layer is made of synthetic materials that resist deterioration from the fluid in the system. The middle layer or layers are made of either fabric or rubber for  low-pressure  systems  or  wire  braid  for  high- pressure   applications.  These layers give the hose its strength. Part of your pre- and post-operational inspections is to inspect hoses for cracking or splitting, pinhole leaks, improper  hose  length,  rubbing,  heat,  twisting,  and  so forth. Any problems with hydraulic hoses should be repaired  before  use. QUICK-DISCONNECT  COUPLERS Quick-disconnect  couplers  (fig.  4-13)  are  used where  hydraulic  lines  must  be  connected  or  dis- connected   frequently; for  example,  in  the  NCF, quick-disconnect   couplers used on front-end loaders Figure  4-12.—Hydraulic  hose  construction. allow quick changing of loader buckets, backhoes, and forklift  attachments. The  quick-disconnect  couplers  are  self-sealing devices that accomplish the work of two shutoff valves and a tube coupler. They are easy to use and keep hydraulic fluid loss at a minimum. More importantly, you do not have to drain or bleed the system each time a  hookup  is  made. Quick-disconnect couplers consist of two halves: the  body  contains  a  spring-loaded  poppet  or  seal,  while the other half is inserted to open the poppet when the two halves are connected. A locking device holds the two halves and seals them. When   quick-disconnect   couplers   are   dis- connected on attachments, you must remember that it is very  important  that dust plugs are inserted in the  coupler  ports.   If dust plugs are unavailable, a common practice is to use a plastic bag to wrap the couplers  in  for  protection  from  foreign  matter. CAUTION Hydraulic  systems  can  create  up  to 3,000 pounds of pressure per square inch and the fluids may reach temperatures above 200°F. Wear protective gloves and use extreme care when  disconnecting  and  reconnecting quick-disconnect   couplers. ACCUMULATORS Accumulators are sometimes placed in a hydraulic system  to  absorb  shock.  These  are  frequently  used  on Figure  4-13.—Quick-disconnect  couplers. 4-11







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