Hydraulic Cylinders & Circuits
Cylinder types, seals, counterbalance valves, regenerative circuits, check valves, and flow dividers.
- Identify cylinder types and explain unequal extend/retract speeds
- Describe seal types, wear patterns, and maintenance practices
- Explain counterbalance valve and check valve functions
- Describe regenerative circuits, flow dividers, and sequence valves
Lesson 1
Cylinder Types & Operation Principles
Hydraulic Cylinder Function
A hydraulic cylinder is the component that converts hydraulic pressure to mechanical force. Oil enters the cylinder under pressure, pushing the piston and extending or retracting the rod. This linear force powers booms, sticks, buckets, blades, and every other working function on heavy equipment.
Single Rod Double Acting Cylinder
A single rod double acting cylinder has unequal extend and retract speeds. Because the rod occupies space on one side of the piston, the effective area is different on each side. The full bore side (without rod) has more area, so the cylinder extends slower (with more force) and retracts faster (with less force) for the same flow rate.
Extension
Full bore area receives oil
More force, slower speed
Rod side oil returns to tank
Retraction
Annular area (bore minus rod) receives oil
Less force, faster speed
Full bore oil returns to tank
Stick Cylinder on Excavator
The stick cylinder on an excavator extends and retracts the stick (dipper arm). It is one of the primary working cylinders and must handle both digging forces and the weight of the stick, bucket, and material.
Speed Difference
A single rod cylinder retracts faster than it extends because the annular area (rod side) is smaller, requiring less oil to fill. This is normal - not a defect.
Cylinders convert hydraulic pressure to mechanical force. A single rod double acting cylinder has unequal extend/retract speeds because the rod reduces the effective area on one side.