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GENERAL DESCRIPTION
Two essentially similar types of hydraulic cylinders are used on the excavator. The cylinder that is used to
operate the excavator boom or bucket is equipped with a rod stopper, which acts as a cushion only when
the cylinder rod is fully retracted (and the bucket is pulled close to the arm). This type of cylinder is shown
in the lower drawing.

Arm cylinders have a cushion or stopper for operation in both directions. This type of cylinder is shown in
the upper drawing.
THEORY OF OPERATION

Cylinder piston rods are extended or retracted
by oil flow to the back side of the cylinder
shown as (“oil path A”) or to the front of the
cylinder (“oil path B”).
The cylinder rod is extended as oil flow is
pumped through the circuit to the back side of
the piston. The force (F1) of the piston stroke
can be expressed by the formula below, where

P = circuit oil pressure and the inside diameter
of the cylinder is expressed by B (Figure 1).
(P: Pressure,

p = 3.14, B: Cylinder Inside
Diameter)
When the cylinder rod is retracted, oil flow
through the circuit from the pump to the front
side of the cylinder generates a force (F2) that
can be expressed by the formula in which the
diameter of the piston rod is expressed by R,
and the other two terms are the same as in the
preceding expression.