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
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 (fig. 4-13) are used
where hydraulic lines must be connected or dis-
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
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.
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
Accumulators are sometimes placed in a hydraulic
system to absorb shock. These are frequently used on
Figure 4-13.Quick-disconnect couplers.