What is Fluid Power?

Fluid Power means exactly what its name might lead you to believe; using fluid to create and transmit power. This makes Fluid Power a type of “power transmission”. There are two types of Fluid Power and each uses a different form of fluid:

Fluid Power has some distinct advantages when compared with other types of power transmission like mechanical or electrical. Using hydraulics or pneumatics, engineers can generate a large amount of power without taking up a lot of space. Fluid Power also makes it relatively easy to control direction, speed, force, and torque, by using simple control valves. Because of its many benefits and uses, Fluid Power is one of the primary sources of power transmission across a variety of industries and applications: Construction, Farming, Mining, Entertainment, and Recycling just to name a few!

Where is Fluid Power Used?

Fluid_Power_excavatorFluid Power is at work behind the scenes just about everywhere – in our vehicles, our schools, and in the machines that package the food we eat, create the clothes we wear, and build the buildings we live and work in. Some common examples include tractors, excavators, factory machines, robots, and even rollercoasters!


Hydraulics is a type of fluid power that uses liquid to create and transfer power through pressure. Machines that use hydraulics are really common, especially in construction equipment. You’ll also find hydraulics being used in different types of bridges, too! Hydraulics_Bridges

The Science of Hydraulics

NFPA_Hydraulics To visualize a basic hydraulic system, think of two identical syringes connected together with tubing and filled with water (see Figure 1). Syringe A represents a pump, and Syringe B represents an actuator, in this case a cylinder. Pushing the plunger of Syringe A pressurizes the liquid inside. This fluid pressure acts equally in all directions (Pascal’s Law), and causes the water to flow out the bottom, into the tube, and into Syringe B. If you placed a 5 lb. object on top of the plunger of Syringe B, you would need to push on Syringe A’s plunger with at least 5 lbs. of force to move the weight upward. If the object weighed 10 lbs., you would have to push with at least 10 lbs. of force to move the weight upward. If the area of the plunger (which is a piston) of Syringe A is 1 sq. in., and you push with 5 lbs. of force, the fluid pressure will be 5 lbs./sq. in. (psi). Because fluid pressure acts equally in all directions, if the object on Syringe B (which, again has an area of 1 sq. in.) weighs 10 lbs., fluid pressure would have to exceed 10 psi before the object would move upward. If we double the diameter of Syringe B (see Figure 2), the area of the plunger becomes four times what it was. This means a 10 lb. weight would be supported on 4 sq. in. of fluid. Therefore, fluid pressure would only have to exceed 2.5 psi (10 lbs. ÷ 4 sq. in. = 2.5 psi) to move the 10 lb. object upward. So, moving the 10 lb. object would only require 2.5 lbs. of force on the plunger of Syringe A, but the plunger on Syringe B would only move upward ¼ as far as when both plungers were the same size. This is the essence of fluid power. Varying the sizes of pistons (plungers) and cylinders (syringes) allows multiplying the applied force.


Pneumatics is a type of fluid power that uses gas, usually air, to generate and transfer power through pressure. You’ll find examples of pneumatics all over your everyday life, with use cases like amusement park rides, factory assembly lines, and even medical equipment. Fluid_Power_Rollercoasters

The Science of Pneumatics

The principles of pneumatics are the same as those for hydraulics, but pneumatics transmits power using a gas instead of a liquid. Compressed air is usually used, but nitrogen or other inert gases can be used for special applications. With pneumatics, air is usually pumped into a receiver using a compressor. The receiver holds a large volume of compressed air to be used by the pneumatic system as needed. Atmospheric air contains airborne dirt, water vapor, and other contaminants, so filters and air dryers are often used in pneumatic systems to keep compressed air clean and dry, which improve reliability and service life of the components and system. Pneumatic systems also use a variety of valves for controlling direction, pressure, and speed of actuators. Even though pneumatic systems usually operate at much lower pressure than hydraulic systems do, pneumatics holds many advantages that make it more suitable for many applications. Because pneumatic pressures are lower, components can be made of thinner and lighter weight materials, such as aluminum and engineered plastics, whereas hydraulic components are generally made of steel and ductile or cast iron. Hydraulic systems are often considered rigid, whereas pneumatic systems usually offer some cushioning, or “give.” Pneumatic systems are generally simpler because air can be exhausted to the atmosphere, whereas hydraulic fluid usually is routed back to a fluid reservoir.