Pneumatic System Components: Types & Functions

A pneumatic system utilizes air pressure to create mechanical motion. A basic pneumatic system consists of an intake filter that traps dirt before it enters the system, an air compressor that provides a source of compressed air, a dryer that removes the moisture in the air, a pressure tank that is a reservoir of compressed air, a pressure regulator that maintains air pressure, a valve that controls the air flow, and a pneumatic cylinder that creates the mechanic motion. An example of a pneumatic system is illustrated below:

A control system that uses pneumatic actuators incorporates a controller along with the pneumatic components as shown in the Figure 1.0 above. The controller specifies when the individual valves in the system are to be turned ON and OFF. Typically, this controller is a digital electronic device such as a microcomputer or a programmable logic controller (PLC). Nevertheless, some controllers are strictly pneumatic devices and employ no electronics at all. Pneumatic controllers utilize pneumatic logic devices – actual AND, OR and NOT gates that operate only on air pressure. The output signals from these controllers are obviously, pneumatic and are conveyed to the control valves through small tubes. While you may find some pneumatic controllers in some legacy systems, generally, the industry has moved away from such kind of controllers to more modern systems employing digital electronic devices.

Pneumatic Systems Components

With reference to the diagrams above, the pneumatic system is made up of several components, and we shall briefly look at them as follows:

Compressors

The air compressor is a machine that pumps the air from the atmosphere into a tank. We different types of compressors, but one of the most commonly used types, is the reciprocating piston compressor.

Receiver Tanks

The receiver tank (pressure tank) receives air from the compressor and becomes the high-pressure reservoir for the system. The figure below shows the compressor and tank system:

Power to the compressor motor is controlled by a pressure switch on the tank. When the tank pressure falls below a set value, the switch closes, and the compressor motor starts. When the pressure increases to a specified value, the pressure switch opens, turning off the compressor.

Dryer       

The dryer is used for removing the moisture in the air. If water vapor is not removed in the compressed air, it will eventually damage the pneumatic components.

There are several types of dryers, for instance, the aftercooler, chills the air, causing the moisture to condense into drops, which can then be drained off. The desiccant dryer circulates the air through a moisture-absorbing chemical called dessicant; when the dessicant becomes saturated (usually indicated by a change in color), it must be changed.

Pressure Regulators

The tank pressure can range anywhere between the high and low limits of pressure switch. Some systems cannot tolerate this variation and thus require a pressure regulator to be installed between the tank and the system components. The pressure regulator can supply air at a constant pressure regardless of the source of pressure as long as the source pressure stays above the desired regulated pressure.

Related: Pressure Regulators: Function & Types

Pneumatic Control Valves

Pneumatic control valves regulate the air flow, which in most cases means ON or OFF. We have a number of possible configurations, for instance, the bidirectional control valve that causes a piston to move in either direction. Pneumatic valves are normally designed to be full or completely OFF and are driven by either an electric solenoid or a pneumatic control signal. These valves require only one tube coming from the air supply; the “utilized” air from the cylinder is simply vented to the atmosphere.

Pneumatic Actuators

Pneumatic actuators convert air pressure into mechanical motion. There are two basic types:

• Linear actuators (cylinder/piston or diaphragm types)
• Rotary actuators

Pneumatic cylinders are available in different shapes and sizes. The double-acting cylinder connects to the valve with two tubes and can be driven in either direction. The single-acting cylinder can only be driven in one direction with air pressure and is returned by a spring.

Related articles:

• How to Minimize Water Vapor in Instrument Air/Pneumatic Systems
• Pneumatic Actuators
• Advantages and Disadvantages of Pneumatic Instruments
• Actuators as Automation Components
• How to Connect a DP (Differential Pressure) Flow Sensor to a DP Transmitter