What Is Hydraulics? How a Hydraulic System Works

Hydraulics is the transmission of power through a pressurised liquid, usually mineral oil. Because oil is practically incompressible, a small pump can drive a cylinder that lifts or presses many tonnes.

The principle is Pascal's law: pressure applied to a confined fluid acts equally in all directions. A Ø100 cylinder at 160 bar produces 12.8 tonnes of force.

Request a Quote

What Is Hydraulics? How a Hydraulic System Works

Pascal's Law and Force Multiplication

If a Ø20 piston and a Ø100 piston share the same oil, the larger one sees the same pressure on 25 times the area, so it pushes 25 times harder. The price is stroke: the small piston must travel 25 times further.

Components of a Hydraulic System

Tank — stores and cools the oil.
Pump — creates flow; pressure builds when the flow meets a load.
Valves — directional, relief, pressure-reducing, flow-control, check and counterbalance valves.
Hydraulic cylinder — produces linear force.
Hydraulic motor — produces rotation.
Filter and accumulator — keep the oil clean and store energy.

Pressure, Flow and Power

Pressure sets the force, flow sets the speed. Power is P [kW] = p [bar] × Q [L/min] / 600: a 20 L/min pump at 160 bar needs about 5.33 kW.

Hydraulic cylinder force at 160 bar
Bore	Force (kN)	Force (t)
Ø40	20.1	2.1
Ø63	49.9	5.1
Ø100	125.7	12.8
Ø160	321.7	32.8
Ø200	502.7	51.3

Open and Closed Circuits

In an open circuit the oil returns to the tank after each cycle; this is the usual layout for presses and industrial machines. In a closed circuit the oil flows directly back to the pump, a layout common in hydrostatic drives of mobile machines.

Where Hydraulics Is Used

Construction and earth-moving machinery
Agricultural machinery and trailers
Presses and metal forming
Lifting, logistics and vehicles
Industrial automation, marine and energy

Frequently Asked Questions

What does hydraulic mean?

Hydraulic means operated by a liquid under pressure. Hydraulic machines use oil pressure to produce force and motion.

What is Pascal's law?

Pressure applied to a confined fluid is transmitted equally in all directions, so a larger piston area gives a proportionally larger force.

What oil is used in hydraulic systems?

Mineral hydraulic oil is the standard medium; its viscosity is chosen for the pump and the operating temperature.

What are the advantages of hydraulics?

Very high force in a compact size, precise control of speed and position, and the ability to hold a load.

Send Us Your Cylinder Data

Bore, rod, stroke, working pressure, mountings and quantity — or a drawing or photo of the cylinder you want to replace. Our engineers reply with a technical proposal and a quotation.

Hydraulic Cylinders Hydraulic cylinder sizes What is pneumatics?