Pneumatic and Hydraulic Systems: Principles and Components

Pneumatic and Hydraulic Fluid Power Systems

Pneumatic and hydraulic fluids are used in machines for specific movements and efforts. Differences: Pneumatic systems use air as the fluid, while hydraulic systems use oil. To generate the air, a compressor is used, whereas a central hydraulic unit is required for hydraulics.

Applications of Fluid Power

Pneumatics: Used for alternative rectilinear and rotational movements of little strength, explosive environments, and tools.

Hydraulics: Used for alternative rectilinear and rotational movements of great strength and precise movements.

Pressure and Force Calculations

Force = Pressure x Area

The pressure can be measured in different units:

• 1 bar = 0.987 atm = 1 kp/cm² = 100,000 Pa = 760 mm Hg

Pneumatic Installation Diagram Components

Compressor + Tank + Line + Air Treatment Group + Valve + Cylinder

In a hydraulic installation, instead of a compressor, a system is used that includes a central reservoir and a hydraulic oil filter. The lines, valves, and cylinders must be much more resistant to withstand high pressures.

Pneumatic Actuators

These are elements that transform the pressure and flow of moving air into power. They can be:

• Double effect: Air must be applied to extend the stem, and applied to the other side to retract it.
• Simple effect: By utilizing an internal spring, one of the two movements is completed when air flow stops into its only port.

Pneumatic Valves

These are elements that disrupt or allow the passage of air between multiple connections. They can have varied appearances and perform basic or complex tasks, such as the control of a cylinder.

The Silencer

A component placed on the exhaust valve to remove noise. In some cases, they are adjustable to restrict the air escape and stop the cylinder.

Specialized Valves

• Check valve: Only lets fluid through in one direction; when fluid attempts to pass in the opposite direction, the ball closes the path.
• Circuit Selector Valve: Features two inputs and one output, but unlike a normal T-connection, the inputs do not communicate with each other.
• Flow control valve: Regulates the flow of air in one direction; usually, the other direction includes a bypass valve to let air pass unregulated.
• Quick exhaust valve: Usually mounted on cylinder connections to greatly accelerate the speed of the cylinder.

Pneumatic Circuits

These usually consist of cylinders and valves to channel air to each cylinder. As the air entering the cylinder must pass through these ducts and valves, the size should be appropriate so as not to restrict the speed of the cylinder. For this reason, these valves and tubes are usually larger.