Hydraulic Cylinders
A hydraulic cylinder is a tube, a piston, and a rod that turns fluid pressure directly into a straight-line push or pull. It is the most common actuator on any heavy machine built after about 1950, because it can deliver enormous force from a compact, sealed package with no gears at all.
01Definition
A hydraulic cylinder is a tube, a piston, and a rod that turns fluid pressure directly into a straight-line push or pull. It is the most common actuator on any heavy machine built after about 1950, because it can deliver enormous force from a compact, sealed package with no gears at all.
02Physical Principle
Pump oil into one side of the piston and it pushes the rod out; pump oil into the other side and it pulls the rod back in — the direction is controlled entirely by a valve, not by the cylinder itself. Because force scales with piston area (Pascal's Law), a boom cylinder only a few hundred millimetres across can lift many tonnes at the far end of an excavator's arm, at working pressures that would be lethal if the seals ever failed.
03Mathematical Foundation
04Interactive Diagram — Hydraulic Cylinder Stroke
Set the cylinder's bore and the pump's flow rate at a fixed 250 bar working pressure to see the force it pushes with, and how fast the rod extends.
Working pressure fixed at 250 bar. Animation speed is illustrative, not real-time.
05Interesting Facts
- A double-acting cylinder — pressurised on both sides in turn — can push and pull with force; a single-acting cylinder can only push, and relies on gravity or a spring to retract.
- The 'stick' cylinder on a large excavator can be over a metre in bore diameter, built more like a piece of pressure-vessel engineering than a typical mechanical part.
- Cylinder seals, not the steel tube, are usually the first thing to wear out on a hydraulic machine — a scored rod as thin as a human hair can leak enough to stall a boom mid-lift.