Definition of Hydraulic & Pneumatic Systems

by Wesley Tucker ; Updated September 26, 2017

Machines of all types need power. Power allows the machines to do specific kinds of work. Two of the most efficient and compact forms of power for machines are hydraulic and pneumatic systems. Hydraulics and pneumatics can be configured into different types of power sources to lift, lower, pull, push, turn, rotate and move machines carrying tremendous loads. Tools can also be powered to break stone, join steel and cut wood. Hydraulics and pneumatics provide the energy to make work happen.


Hydraulics work on the principle of pressurized fluid forcing mechanical action. A hydraulic system installed on a machine is called a hydraulic circuit. Hydraulic circuits are composed of a pump to compress the fluid, lines to carry the fluid, a cylinder where the fluid is pumped and a piston moved by the pressurized fluid in the cylinder. Hydraulics can also actuate shafts to power hydraulic motors and conveyors.


Pneumatics are similar to hydraulics with one major difference: Instead of fluid, pneumatics use gas (usually air). Air is pulled into a compressor and is then forced through lines to different tools. The compressed air actuates pistons and shafts and forces them to move. Pneumatics are often used for different kinds of hand tools and also for machines doing repetitive motion. A jackhammer is a good example of a repetitive pneumatic tool.

Video of the Day

Brought to you by Techwalla
Brought to you by Techwalla


Beyond the difference of liquid and gas, there are other differences between pneumatics and hydraulics. Hydraulics are a closed circuit: fluid is sent to the cylinder, moves the piston and then circulates back to the pump. Pneumatics on the other hand “breathe” and do not circulate the air. The compressed air is sent to the tool to do work and then expended through an exhaust port. More air is pulled into the compressor when doing more work.

Hydraulic Installations

Hydraulics are installed to do heavy work on a variety of vehicles and production machinery. Pressurized hydraulic fluid can withstand tremendous loads and relatively small circuits can lift and move many tons of material. Hydraulics are also used for machines doing stamping, pressing and rolling work, as in a steel mill or fabrication facility. Hydraulic circuits are also used in cars, trucks and aircraft to actuate various systems, such as brakes, lifts and control surfaces (flaps).

Pneumatic Installations

Pneumatic systems are used in all types of assembly and fabrication installations. The repetitive action pneumatics supply is ideal for tools such as drills, hammers and chisels. Pneumatics are also installed to move items on assembly lines and in maintenance facilities, such as garages and aircraft hangars.

About the Author

Wesley Tucker is a lifelong southerner whose politics are objective, whose sports are many and whose avocations range from aviation to anthropology to history and all forms of media. With a master's degree in mass communications from the University of South Carolina College of Journalism, Tucker has been a writer for more than 30 years, with work ranging from news reports to feature stories.

Cite this Article A tool to create a citation to reference this article Cite this Article