How Hydraulic Cylinders Work
A hydraulic cylinder is a piston in a sealed tube. Pressurized oil pushes on the piston. The piston pushes on the rod. The rod moves loads. How much force the cylinder puts out depends on three things: pressure, bore size, and which way it is moving.
Extend vs Retract Force
The extend side is the full bore area. The retract side has the rod taking up space, so the working area is smaller. This makes extend force bigger than retract force. A 3 inch bore with a 1.5 inch rod has about 25 percent less retract force than extend force.
Flow and Speed
Cylinder speed comes from oil flow. The faster the oil flows in, the faster the cylinder extends. For a given flow, a bigger bore moves slower because the oil has to fill more space. This calculator gives you the flow rate needed for your target speed.
Pro tip: If you need equal extend and retract speeds, use a double-rod cylinder. Both sides have the same working area so speeds and forces match.
Picking the Right Cylinder
Start with the load. Divide the load by the operating pressure to get the required area. Pick a bore that gives at least that area. Add a safety factor of 1.25 to 2.0 for real applications. Then pick a rod that handles any tension load without buckling.
Common Applications
Hydraulic cylinders power presses, lifts, excavators, and automation. In machine tools they clamp parts. In robots they move arms. In cars they press brake pads. Any job that needs high force in a small package often uses hydraulics.