Return to Master Table of Contents 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). Figure 1 F 1 = P x π B 4 2 = 3.14, B: Cylinder Inside Diameter) (P:
Pressure, π 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. Figure 2 F 2 = P x π (B 2 ) 4 -R 2 S0705000 Page 3 Cylinders 1. Piston 2. Oil Path A 3. Oil Path B 1. Cylinder Inside Diameter - B 2. Oil Path A 3. Oil Path B 4. Rod Diameter