What is fluid power?

Fluid power is energy transmitted and controlled by means of a pressurized fluid, either liquid or gas. The term fluid power applies to both hydraulics and pneumatics. Hydraulics uses pressurized liquid, for example, oil or water; pneumatics uses compressed air or other neutral gases. Fluid power can be effectively combined with other technologies through the use of sensors, transducers and microprocessors.

How fluid power works

Pascal's Law expresses the central concept of fluid power: "Pressure exerted by a confined fluid acts undiminished equally in all directions."

An input force of 10 pounds (44.8 N) on a 1-square-inch (6.45 cm²) piston develops a pressure of 10 pounds per square inch (psi) (68.95 kN/m² or 68.95 KPa) throughout the container. This pressure will allow a 10-square-inch piston to support a 100-pound (444.8 N) weight. The forces are proportional to the piston areas.

The advantages of fluid power

Fluid power systems provide many benefits to users including:

• Multiplication and variation of force-Linear or rotary force can be multiplied from a fraction of an ounce to several hundred tons of output.
• Easy, accurate control-You can start, stop, accelerate, decelerate, reverse or position large forces with great accuracy. Analog (infinitely variable) and digital (on/off) control are possible. Instantly reversible motion-within less than half a revolution-can be achieved.
• Multi-function control-A single hydraulic pump or air compressor can provide power and control for numerous machines or machine functions when combined with fluid power manifolds and valves.
• High horsepower, low weight ratio-Pneumatic components are compact and lightweight. You can hold a five horsepower hydraulic motor in the palm of your hand.
• Low speed torque-Unlike electric motors, air or hydraulic motors can produce large amounts of torque (twisting force) while operating at low speeds. Some hydraulic and air motors can even maintain torque at zero speed without overheating.
• Constant force or torque-This is a unique fluid power attribute.
• Safety in hazardous environments-Fluid power can be used in mines, chemical plants, near explosives and in paint applications because it is inherently spark-free and can tolerate high temperatures.
• Established standards and engineering-The fluid power industry has established design and performance standards for hydraulic and pneumatic products through NFPA, the National Fluid Power Association and ISO, the International Organization for Standardization.

Fluid power applications

• Mobile: Here fluid power is used to transport, excavate and lift materials as well as control or power mobile equipment. End use industries include construction, agriculture, marine and the military. Applications include backhoes, graders, tractors, truck brakes and suspensions, spreaders and highway maintenance vehicles.
• Industrial: Here fluid power is used to provide power transmission and motion control for the machines of industry. End use industries range from plastics working to paper production. Applications include metalworking equipment, controllers, automated manipulators, material handling and assembly equipment.
• Aerospace: Fluid power is used for both commercial and military aircraft, spacecraft and related support equipment. Applications include landing gear, brakes, flight controls, motor controls and cargo loading equipment.

Fluid power products

Fluid power products are sold as individual components or as systems for the original equipment manufacturing, maintenance, repair and replacement markets.

A typical fluid power system includes the following components:

• Hydraulic pump or air compressor, which converts mechanical power to fluid power.
• Cylinder or motor, which converts fluid power to linear or rotary mechanical power.
• Valves, which control the direction, pressure and rate of flow.
• Filters, regulators and lubricators, which condition the fluid.
• Manifolds, hose, tube, fittings, couplings, etc., which conduct the fluid between components.
• Sealing devices, which help contain the fluid.
• Accumulators and reservoirs, which store the fluid.
• Instruments such as pressure switches, gauges, flow meters, sensors and transducers, which are used to help monitor the performance of a fluid power system.