How Does a Hydraulic Cylinder Work?
A hydraulic cylinder converts the energy of pressurised oil into linear force and motion. Pump flow enters the cylinder, pressure acts on the piston and the rod pushes or pulls the load. Because oil is practically incompressible, a compact cylinder can deliver many tons of force with precise control.
This guide explains the working principle, the parts of a cylinder, the main types and the formulas for force and speed.
The Working Principle
Hydraulics is based on Pascal’s law: pressure applied to a confined fluid is transmitted undiminished throughout the fluid. A pump delivers oil, a directional valve routes it to one side of the piston, and the pressure acting on the piston area creates force: F = P × A.
Oil on the opposite side is pushed back to the tank. Reversing the valve sends oil to the other side and the rod moves in the opposite direction. The speed of the rod depends on flow: v = Q / A.
Example: at 160 bar (2,320 psi) an 80 mm (3.15 in) bore generates about 80.4 kN, or 8.2 metric tons. With a 40 L/min (10.6 GPM) pump it extends at roughly 0.13 m/s (5.2 in/s).Parts of a Hydraulic Cylinder
Barrel
Honed steel tube that contains the pressure; its inner finish determines seal life.
Piston
Separates the two chambers and converts pressure into force.
Piston rod
Induction-hardened, hard-chromed rod that transmits force to the load.
Cap and head
Close the barrel; the head guides the rod and carries rod and wiper seals.
Seals
Piston, rod, wiper and static seals prevent internal and external leakage.
Mountings
Eyes, clevises, flanges, trunnions or feet connect the cylinder to the machine.
Main Types
Single acting
Pressure in one direction, return by load or spring. See single acting cylinders.
Double acting
Pressure in both directions. See double acting cylinders.
Telescopic
Multi-stage for long strokes. See telescopic cylinders.
Tie-rod
ISO-standard industrial design. See tie-rod cylinders.
Welded
Compact design for mobile equipment. See welded cylinders.
Ram / plunger
Rod as working area; for jacks and lifts.
Force by Bore Size
Theoretical push force.
| Bore | 160 bar (2,320 psi) – metric t | 160 bar – US tons | 250 bar (3,625 psi) – metric t |
|---|---|---|---|
| 40 mm | 2.1 t | 2.3 US tons | 3.2 t |
| 50 mm | 3.2 t | 3.5 US tons | 5.0 t |
| 63 mm | 5.1 t | 5.6 US tons | 7.9 t |
| 80 mm | 8.2 t | 9.0 US tons | 12.8 t |
| 100 mm | 12.8 t | 14.1 US tons | 20.0 t |
| 125 mm | 20.0 t | 22.1 US tons | 31.3 t |
| 160 mm | 32.8 t | 36.2 US tons | 51.3 t |
| 200 mm | 51.3 t | 56.5 US tons | 80.1 t |
Common Problems and Their Causes
- Rod seal leakageWorn seal or scratched rod, often from dirt or side load.
- Cylinder drifts under loadInternal leakage past the piston seal or valve leakage.
- Jerky motionAir in the oil, low flow or high seal friction.
- Bent rodBuckling on a long push stroke or side loading.
- OverheatingOil temperature too high, hardening seals.
Need a Hydraulic Cylinder?
Fenitsa manufactures standard and custom hydraulic cylinders in Türkiye and exports worldwide.
Hydraulic Cylinder FAQ
What is the basic principle of a hydraulic cylinder?
Pascal’s law: pressure applied to a confined liquid is transmitted equally in all directions. Oil pressure acting on the piston area produces a force F = P × A.
What are the main parts of a hydraulic cylinder?
Barrel (honed tube), piston, piston rod (hard-chromed), cap and head, seals, guide rings or bushings and mountings.
What determines cylinder speed?
Flow rate divided by the effective area: v = Q / A. Larger bores are stronger but slower for the same flow.
Why do hydraulic cylinders leak?
Worn or damaged seals, scratched rods, contaminated oil and side loads are the most common causes of internal and external leakage.
Hydraulic cylinder vs hydraulic ram: are they the same?
In everyday use yes. Strictly, a ram is a single acting cylinder in which the rod itself is the working area.