Numatic Systems: Compressed Air Principles, Components and Applications

Pneumatics is the branch of technology that studies the use of pressurized gas, usually air, to transmit energy and perform mechanical work in industrial studio techniques and practical applications. Pneumatic installations use compressed air circuits to generate motion and force from an abundant and inexpensive energy source.

Compressed air: Atmospheric air is an abundant element, easily stored, and its natural properties make it an ideal fluid. Air can be compressed by a mechanical action from the outside. In a cylinder, the air inside is compressed and, as the volume decreases, the pressure rises, producing a force on the piston rod. The force applied by the cylinder equals the pressure multiplied by the effective surface area of the piston.

Formula: if the temperature inside the cylinder remains constant, the product of the absolute pressure and the volume is a constant amount that determines the gas: P × V = constant.

Formula: P1 × V1 = P2 × V2, where P represents absolute pressure, V represents volume, and T represents absolute temperature in Kelvin (T = °C + 273).

Pressure units:

• Pascal (Pa): The pressure exerted by a force of one newton distributed over a surface of one square meter.
• Atmosphere (atm): Equivalent to the atmospheric pressure at sea level.
• Millimeter of mercury (mmHg): The pressure that a column of mercury of one millimeter height exerts inside a glass tube.

Atmospheric pressure varies with altitude. Pressure gauges measure the difference between the pressure of a system and atmospheric pressure; this value is called relative pressure.

Obtaining compressed air: Compressed air is obtained by means of compressors, which increase the pressure of atmospheric air drawn in from the environment.

Formula: Q = v × S, where Q is the volumetric flow of the fluid, S is the cross-sectional area of the pipe in m², L is the length of the pipe in meters, t is time in seconds or minutes, and v is the velocity of the fluid movement.

Compressed Air Controllers

Pressure regulator: Its function is to control pressure in a pneumatic circuit. The pressure switch maintains the pressure inside the tank within set limits by connecting or disconnecting the air supply device.

Safety valve: When the pressure inside the tank exceeds the calibrated pressure, the safety valve releases air to the outside.

Conditioning Unit

Filter: Its function is to clean compressed air and remove all impurities, such as solid particles and water in suspension.

Pressure regulator: Air enters the filtered regulator, whose mission is to keep the output pressure stable and constant.

Lubricator: Pneumatic elements must be lubricated. After filtering and regulating, the air passes through the lubricator, which adds a fine oil mist to the air flow.

Pneumatic Actuators

Single-Acting Cylinders

These cylinders can perform useful work only in one direction of movement. The return stroke is produced by a spring or by the external load, and the air is evacuated to the atmosphere from the rear part of the piston. They are used for applications that require short displacements.

Double-Acting Cylinders

These cylinders can produce useful work in both directions, with active force on both the forward and return strokes. They are built with a piston and a rod, and compressed air is applied alternately on each side of the piston to move it forward and back to its initial position.

Formula:
Piston force = pressure × effective piston area − friction losses (including seal friction).

Piston force depends on the pressure of the air and the effective surface area of the piston. Friction in the seals reduces the actual force delivered.