General Description; Theory Of Operation - Doosan DX140R Shop Manual

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

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2
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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 D (Figure 1).
(P: Pressure, π = 3.14, D: Cylinder Inside Diameter)
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2
3
4
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.
F
2
Cylinders
Page 6
Piston
Oil Path A
Oil Path B
πD
2
F = P x
1
4
Cylinder Inside Diameter - D
Oil Path A
Oil Path B
Rod Diameter - R
π(D 2 2
= P x -R )
4
1
D
2
Figure 1
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2
Figure 2
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FG001456
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3
FG001458
SP000030