Pneumatic Systems

Pneumatic systems are defined as systems that operate using compressed air. Pneumatic systems typically include cylinders, valves, and other mechanical components actuated by air or gas pressure movement.

Compared to other energy sources, air energy is readily available, inexpensive, and can be easily obtained and stored from the atmosphere using appropriate methods, then released back into the atmosphere. The abundance of air in the atmosphere and its low cost of acquisition ensure its economic advantage. Pneumatic systems are used in a variety of operations across nearly all areas of industry, including clamping and releasing workpieces, moving them, and generating linear and rotational motion such as.

Principle of Operation of Pneumatic Systems

The fundamental work principle of pneumatic systems is to use the pressure of air or gas to move a piston within a cylinder. This movement causes linear motion by pushing or pulling the piston inside the cylinder force. Force is applied at an output connection point from which mechanical motion is generated.

Pneumatic systems generally consist of a compressor, an air reservoir, a control valve, and a cylinder or actuator. The compressor compresses atmospheric air or gas and delivers it to the air reservoir atmospheric pressure. The air reservoir stores the compressed air or gas and prepares it for use. The control valve regulates the flow of air pressure from the reservoir to the cylinder. The cylinder or actuator then converts the air or gas pressure into mechanical motion.

Structure and Operational Characteristics of Pneumatic Circuit Components

Preparation of Compressed Air

Compressed air used in pneumatic systems is supplied by compressors. Air compression is typically provided by a centralized pressure source and delivered to the system via pipes or hoses. This eliminates the need for individual pressure sources for each user. Portable compressors are used for machines or hand tools that require mobility Place.

In selecting a compressor, determining the facility’s air demand (capacity) is a critical important factor. Choosing a compressor with lower capacity than required reduces efficiency and shortens the compressor’s lifespan due to frequent cycling. Choosing a compressor with significantly higher capacity than needed increases investment and operating costs.

Compressed Air Distribution Diagram (Credit: Electrical and Electronic Technology, MEB, 2011.)

Distribution and Conditioning of Compressed Air

For optimal efficiency, compressed air produced in pneumatic systems must be distributed in a way that minimizes losses. When assessing current system requirements, future growth potential must also be considered. The system should be designed with forward-looking planning from the outset. Potential leaks in the compressed air distribution network must be anticipated from the beginning. Otherwise, future maintenance expenses and additional system installations may result in significantly higher costs.

Compressed air distribution network (Credit: Electrical and Electronics Technology, MEB, 2011.)

Air reservoirs are installed at the outlet of compressors. They prevent pressure fluctuations, provide additional surface area for cooling compressed air, and facilitate the condensation and separation of moisture within the reservoir.

Air reservoirs can be horizontal or vertical. The air outlet must always be located at the top of the reservoir to prevent condensed water from entering the system.

Installation configurations of compressed air reservoirs (Credit: Electrical and Electronics Technology, MEB, 2011.)

Air Drying

Three method methods are used for air drying.

Chemical Method

In this drying method, air is passed through a chemical substance that forms compounds with water vapor. This chemical substance is known as “salt” or NaCl. Water vapor in the air reacts chemically with this substance as it passes through, separating from the air and collecting as a solution at the base of the dryer. The solution is periodically drained. Since salt gradually depletes, it must be replenished at regular intervals. The temperature of the incoming compressed air must not exceed 30°C. A filter must be installed after the dryer to remove any salt particles that may become airborne. In this method, oil is also separated. Due to the potential negative impact of excessive oil on the dryer, a fine filter must be installed at the inlet.

Physical Method

In this method, air is passed through a material composed of silicon dioxide (silica gel), which absorbs water vapor. The drying agent exists as granules within the dryer. This method involves no chemical reaction. Silica gel changes color upon contact with water vapor. Once it reaches saturation, the moisture within it must be removed. For this purpose, two parallel dryers are typically used. The saturated dryer is taken offline and regenerated by passing hot or cold air through it, removing the moisture. The regenerated silica gel returns to its original color. Meanwhile, the other dryer remains in operation. Over time, silica gel may wear down due to air flow and become airborne; therefore, a filter must be installed at the outlet. Silica gel contaminated or worn by oil and other impurities should be replaced every 1 to 2 years.

Chemical Drying Method and Physical Drying Method (Credit: Electrical and Electronic Technology, Ministry of National Education, 2011.)

Cooling Method

This method is based on cooling air to its dew point temperature. Incoming air is first cooled slightly in a heat exchanger, then further cooled to approximately 1.7–5°C in a refrigeration unit. Water vapor condenses and separates from the air due to cooling. The cooled air is then used to pre-cool the incoming air. A filter is used to remove contaminants and oil particles from the cooled air. This method captures 80–90% of the oil originating from the compressor. It is the most widely used drying method due to its economic efficiency.

Cooling Method (Credit: Electrical and Electronics Technology, MEB, 2011.)

Air Preparation Components

Air delivered to the point of use passes through a conditioning unit consisting of a filter, pressure regulator, and lubricator to achieve its final characteristics. This assembly is commonly referred to as an FRY unit (Filter, Regulator, Lubricator).

Filter

The first component of the air preparation unit. Filters are used to remove foreign matter and moisture from compressed air. As air enters the filter through an inlet channel, it acquires a swirling motion. Solid particles and water collect on the inner surface of the housing due to centrifugal force. The air then passes through a sintered bronze filter element before exiting the filter. There are two methods for draining accumulated water from the housing. In manually drained filters, water must be drained before reaching the permissible level by opening the drain valve located at the bottom of the housing. In automatically drained filters, this process occurs automatically without human intervention.

Regulator

Each pneumatic circuit has an optimal operating pressure. Excessively high pressure causes energy loss and quick wear, while excessively low pressure results in failure to perform the intended function or at least reduced efficiency. Since pressure in the compressor reservoir constantly fluctuates, a pressure-reducing valve (regulator) is required to prevent these fluctuations from affecting the system. Regardless of the inlet pressure, the outlet pressure remains constant at the value set on the regulator’s manometer. Regulators are classified into two types: vented and non-vented.

Lubricator

Lubricating the air used in pneumatic systems offers advantages such as minimizing wear, reducing friction losses, and providing corrosion protection. Lubricators typically operate on the Venturi principle. As air passes through a narrow section, its velocity increases and pressure drops. This pressure drop creates suction from a fine oil line, causing oil to drip into the air stream. However, for dripping to occur, the air flow rate must exceed a minimum threshold; otherwise, the pressure drop is insufficient to draw oil. For proper lubrication, the lubricator’s adjustment screw is typically set to deliver 1–12 drops per 1000 liters of air. The viscosity of the lubricating oil at 20°C should be between 10–50 cSt. The distance between the conditioning unit and the farthest user should not exceed 5 meters; beyond this distance, the effectiveness of the atomized oil diminishes.

Pneumatic Component Internal Structures

Pneumatic System Schematic (Credit: Maktology)

Pneumatic Cylinders

Pneumatic cylinders convert compressed air energy into linear pushing or pulling motion. A pneumatic cylinder consists of front and rear caps, a cylinder barrel, a piston rod, and sealing elements.

• Single-Acting Cylinder: In this type, compressed air acts in only one direction, meaning there is only one port for air inlet and outlet. Thus, motion is generated in only one direction. The return stroke of the piston rod is achieved either by a spring or an external force such as the weight of the load. Sometimes the spring is mounted on the piston side to provide a pulling action. The spring stiffness is selected to ensure the piston rod is pushed with sufficient speed.

• Double-Acting Cylinder: In this type, the force generated by air pressure and piston surface area moves the piston rod in both directions, enabling work to be performed in both directions. The force in each direction differs depending on the surface area exposed to pressure. There are two inlet and outlet ports on the cylinder. Double-acting cylinders are used especially when work must be performed during the return stroke. During operation, when air is supplied to the piston side, air on the piston rod side is exhausted, or vice versa.

• Cushioned Type Cylinders: When heavy loads are moved by a cylinder, cushioning is applied at the end of the stroke to prevent impact or damage. Before reaching the end of the stroke, a cushion pad closes the normally free exhaust port. As a result, air can only escape through a very small, often adjustable orifice. The trapped air mass compresses between the piston and the cylinder cap. During the return stroke, air passes through a check valve to continue its flow. Cushioning can be applied in one or both directions.

• Double-Rod Cylinder: In this cylinder, the piston rod is supported on both ends. This arrangement counteracts lateral loads. Since the surface areas on both sides are identical, the forces and speeds generated are equal.

• Tandem Cylinder: This cylinder contains two double-acting cylinders connected in series within the same body. Air is simultaneously supplied to the piston rod sides of both cylinders. This effectively doubles the surface area exposed to air pressure, thereby increasing the force on the piston rod. These cylinders are used when the piston diameter is too large or when space constraints prevent installation of a single large cylinder.

• Multi-Position Cylinders: These consist of at least two double-acting cylinders mounted sequentially within the same body. One cylinder’s piston rod is fixed to a pivot, and work is performed by the other cylinder’s piston rod. In some applications, the number of cylinders is increased further to achieve up to 12 positions.

• Rotary Cylinder: In this variant of the double-acting cylinder, the piston rod end has a toothed profile that drives a gear, converting linear motion in both directions into rotary motion. Common angular displacements are 45°, 90°, 180°, 270°, and 720°. These cylinders are used for pipe bending, workpiece rotation, air conditioning control, and valve actuation.

Pneumatic Cylinder Types (Credit: Electrical and Electronics Technology, Ministry of National Education, 2011.)

Pneumatic Motors

Air motors convert compressed air energy into rotary motion. Their most important features are their compact size relative to their power output and their ability to be easily controlled over a wide speed range due to their suitable moment characteristics. These motors can operate under harsh conditions involving heat, moisture, dirt, and vibration, and can be loaded to a complete stop without damage. They do not emit toxic gases and pose no explosion risk. Due to their adaptability to various applications, air motors are used across a broad spectrum, from large cranes on oil drilling platforms to motorized air screwdrivers small.

• Radial Piston Motors: In piston motors, the energy of air is converted into mechanical rotary motion via pistons and a crankshaft. A large number of pistons are required for smooth operation. The motor’s power depends on inlet pressure, number of pistons, piston surface area, and piston speed.

• Axial Piston Motors: The operating principle of axial piston motors is the same. For smooth operation and balanced torque distribution, two pistons are pressurized simultaneously. These air motors can be set to rotate clockwise or counterclockwise and typically operate at speeds up to approximately 5000 rpm. They are used in heavy-duty applications such as cranes, concrete breaking, and drilling.

• Vaned (Vane) Air Motors: Their simple construction and low weight make them preferred. The sliding vane type is widely used. A rotor is mounted eccentrically within a cylindrical chamber. Vanes are fitted into slots on the rotor. During operation, centrifugal force pushes the vanes against the inner wall of the cylinder, creating a seal. These motors operate between 3000 and 9000 rpm and can rotate in both directions.

• Gear Air Motors: Rotational motion is achieved by two intermeshing gears subjected to air pressure. One gear is connected to the output shaft. They are manufactured in spur, helical, and double-helical configurations. They are used in applications requiring high power. Due to these characteristics, they are employed in mining, conveyor belt systems, drilling and breaking tools, petrochemical industries, iron and steel industries, and in cranes, overhead bridges, mixers, and large diesel engine starter systems.

• Turbine-Type Motors: These operate on the reverse principle of axial compressors. They are used in applications requiring low power and feature very high rotational speeds, capable of reaching up to 500,000 rpm, similar to dental drills. They are used for diamond cutting, grinding, and dental milling.

Pneumatic Motor Types (Credit: Electrical and Electronic Technology, Ministry of National Education, 2011.)

Directional Control Valves

Pneumatic control circuits consist of a signal element, a control element, and an actuating element. The signal and control elements govern the motion of the actuating element. In pneumatic applications, these are called valves. A valve controls the pressure, flow rate, direction, and start-stop conditions of the fluid coming from a pump or pressurized tank. Valves are classified into three groups according to their operating principles: directional control valves, flow control valves, and pressure control valves.

In schematic representation, valves are depicted using squares. These squares indicate the valve’s function, not its construction.

Directional Control Valves

Directional control valves are manufactured in two construction types: seated valves and sliding valves.

• Seated Valve: In this type, the flow passage is closed by a ball, disc, plate, or plug. A seal is used for leak prevention. Since there are no interacting internal components, they have a long service life and are not sensitive to dirt or dust. The force required to actuate the valve varies with the stiffness of the internal spring.

• Sliding Valve: In this type, a control piston (sliding spool) connects each line. Sealing is achieved by O-rings placed on grooves of the spool. Sometimes a bronze bushing is inserted into the valve body to allow the O-rings to slide smoothly. This ensures good sealing and reduces the force required to move the spool.

Directional Control Valves (Credit: Electrical and Electronics Technology, MEB, 2011.)

Pressure Control Valves

Pressure control valves are rarely used in pneumatic systems. A Security valve releases air to the atmosphere when the pressure reaches a preset value. They are used on air receivers.

• Check Valve: This valve allows fluid flow in one direction only and blocks it in the reverse direction. Also known as a non-return valve. They are manufactured as either ball-type or flap-type. Initially, a spring pushes the flap against the flow passage. When air pressure from the left overcomes the spring force, the element moves right and opens the passage. When air is supplied from the right, the air pressure and spring force together close the passage.

Pressure Control Valves (Credit: Electrical and Electronics Technology, Ministry of National Education, 2011.)

Flow Control Valves

• Speed Control Valve: This component, which contains a check valve, regulates the speed of the actuating element by restricting flow in one direction. In the restricted direction, fluid is forced to pass through an adjustable orifice. In the opposite direction, the check valve opens, allowing unrestricted flow.

• Flow Restriction Valve: This valve is used when speed control is required at any point in the stroke of single-acting or double-acting cylinders. In double-acting cylinders, it may be used for cushioning when controlling large masses. For this purpose, a cam mechanism mounted on the piston rod presses against the valve’s roller, pushing a conical adjustment spool downward, thereby achieving the desired speed control. The adjustment can be made by changing the cam’s contact length or the roller’s contact depth with the spool. Due to the internal check valve, speed control is possible in only one direction.

• Quick Exhaust Valve: Used to increase cylinder speed. In some applications, no work is performed during the return stroke, and minimizing this idle time is desired. The quick exhaust valve is mounted close to the cylinder. Thus, air from the cylinder is exhausted through the quick exhaust valve rather than through the directional control valve. The valve has three connections: P, A, and R. The A line connects to the cylinder. The R line is open to the atmosphere. When pressurized air is supplied through the P line, the internal movable sealing element closes the R port, allowing air to fill the cylinder. During return, when pressure is present in the A line, the movable element closes the P port, allowing the air in the cylinder to rapidly exhaust through the R port.

• OR Valve: This is a logic valve used in pneumatic circuits. It has three air connection ports: X and Y are inlet ports, and A is the outlet. By design, air supplied to either X or Y results in an output at A. Thus, air signal at either inlet port is sufficient to produce an output at A.

• AND Valve: This logic valve also has three air connection ports: X and Y as inlets, and A as the outlet. However, an output at A is obtained only when air is supplied simultaneously to both X and Y. If air is present only at X, the internal movable element blocks the connection between X and A, preventing output at A. Only when air is also supplied to Y will output occur at A. The same applies if air is supplied only to Y.

Flow Control Valves (Credit: Electrical and Electronic Technology, Ministry of National Education, 2011.)

Advantages of Pneumatic Systems

• Air, the source of pneumatic energy, is available in unlimited quantities in the atmosphere.
• Air is clean and does not pollute the environment.
• Speed and force can be adjusted to suit the application.
• Compressed air can be transported over long distances.
• High speeds can be achieved with pneumatic systems.
• There is no risk of electric shock from compressed air fire.

Disadvantages of Pneumatic Systems

• Due to the compressibility of air, piston speed cannot be precisely maintained at all desired values time.
• Operating pressure is typically limited to 6–7 bar, making it difficult to generate large forces.
• Air is exhausted to the atmosphere after performing its function, resulting in air consumption.
• Without a muffler on the exhaust line, noisy operation occurs.

Applications of Pneumatic Systems

Pneumatic systems, widely used in industrial applications, are continuously updated and improved to enhance efficiency. The primary sectors using these systems are automation and robotics. Other sectors include food processing, textiles, cleaning, painting, filling, and packaging machinery, assembly lines, and industrial machinery.