The basic principle.
A confined fluid transmits pressure. For a piston with pressure on one side, the ideal force is pressure multiplied by effective area: F = pA. If both sides are pressurised, their opposing forces must be considered.
Pressure acts in every direction, not just upwards. Cylinder walls and seals contain it while the moving piston or plunger converts it into useful force. The structure carries the resulting reaction loads.
An ideal piston calculation.
A pressure of 2 MPa acting on 0.01 m² produces 20,000 N. This ignores friction, opposing pressure and dynamic effects.
Follow the relationship.
- PressureActs on the effective area.
- AreaSets force for that pressure.
- ForceMoves or supports the load.
Connect it to the lift.
A larger area gives more force at the same pressure, but also requires more fluid for the same travel. Hydraulic force multiplication does not create energy: a smaller input piston must move further to supply the larger piston’s volume.
A closer look
Liquids are often treated as incompressible in introductory examples. Real fluids compress slightly, and entrained air can substantially change stiffness and response.
Check your understanding
Does doubling piston area double its speed at the same flow?
Reveal the explanation
No. It doubles ideal force at the same pressure, but halves speed at the same flow.