Fluid Systems

Students explore hydraulic and pneumatic systems.


In this lesson we will explore how hydraulic and pneumatic systems (or fluid systems) work, what principles they follow and how to construct such a system.

Hydraulic Systems

Hydraulics is the study of pressure in liquids. Devices that transmit applied forces through a liquid to move something else, because of pressure, are called hydraulic systems. In most hydraulic systems, a force is exerted on a continuous, enclosed liquid. The applied force creates pressure that moves the liquid through a series of tubes, pipes, or hoses, which causes motion at the other end of the system.

Hydraulics to Transport Fluids

Just as water gushes out of an open faucet, liquids under pressure flow away from the applied force in all directions. Hydraulic systems can be used to transport fluids over large distances. The ancient Romans constructed huge aqueducts to transport water from lakes to distant cities. Today, water, natural gas, and oil are typical examples of fluids transported in extensive pipelines. Pumps provide the force that pushes the fluid through the pipes. Why do the travelling fluids need to be placed under pressure? Think about the water that comes out of your faucet. How does water travel up to reach homes in highrise apartment buildings? To travel so high, water must be placed under pressure in order to move against gravity. There must be enough pressure in the pipes to transport the liquid over a large distance, but not enough to burst the pipes. Friction in the pipes — caused by rough surfaces or numerous bends in the pipeline — can affect fluid pressure. Particles lose energy as they brush past each other in confined spaces and as they bump into the walls of the pipelines.

Pressure and Pneumatic Systems

Pneumatic systems are similar to hydraulic systems, except gases are used instead of liquids. The operation of most pneumatic systems is based on the fact that gases can be compressed. Therefore, compressors — devices that compress air — are needed. Air pressure builds up in these devices. As the pressure is released, the compressed air decompresses. In other words, the particles start to move apart suddenly, creating a strong, steady force that can perform powerful tasks. Many tools use pneumatics, from large tampers used to pack down dirt and gravel when building a road, to tiny precision drills used by dentists. As well, heavy trucks and buses rely on pneumatic brakes (also called air brakes) to stop quickly and smoothly.

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