Copyright Goodheart-Willcox Co., Inc.
132 Hydraulic Systems for Mobile Equipment
Operation and Inherent Benefi t
The cylinder extends in stages. The cylinder’s operation has benefi ts that are
inherent to its design. The larger-diameter stages extend fi rst, because they have
the most effective area. The smaller stages extend last. During the initial exten-
sion the cylinder extends at the slowest speed and with the most force. This oper-
ation is benefi cial in a dump truck because it provides smooth and safe extension
while the bulk of the load begins to move. A smaller-diameter stage will extend
next, causing the cylinder to extend faster with less force. This operation is ben-
efi cial because the bulk of the load has been dumped, and an increase in speed is
more desirable than greater force as the remaining payload is dumped.
Trash trucks use double-acting telescoping cylinders to actuate the com-
pactor. This cylinder provides the inherent benefi t of large forces during com-
paction. The cylinder also provides a fast retraction speed with a reduced force.
The compactor needs little force for retraction because the load exists only
during extension. See Figure 6-11.
Figure 6-12 shows hydraulic hoses attached to the plunger of a double-
acting telescoping cylinder. The fl uid passageways are drilled through the cyl-
inder’s plunger.
Cylinder Components and Nomenclature
A hydraulic cylinder contains several individual components: piston,
gland, rod, barrel, and seals. The cylinder’s piston is secured to the cylinder’s
rod by a nut or a bolt. See Figure 6-13.
Piston Rings and Seals
Pistons have multiple rings and seals installed around their outside circum-
ference. A piston wear ring prevents the piston from rubbing the barrel. A piston
Extend Retract
Figure 6-11. Double-acting telescoping cylinders have the oil routed internally through the cylinder. The effective area
for retraction is small, resulting in fast retraction speeds with reduced force.