Pneumatic and Hydraulic Circuit Design & Applications

Pneumatic and Hydraulic Circuits: Design & Components

Pneumatic and hydraulic circuits consist of all components necessary to perform the movement or rotation of an actuator. Depending on the medium used, they are classified as pneumatic (using compressed air), hydraulic (using pressurized fluid like oil), or mixed systems.

The primary differences between pneumatic and hydraulic systems lie in their pressure source and the collection of oil in tanks for hydraulic systems; however, many of their components share similar symbolic representations.

Movement Diagrams

A movement diagram illustrates the position and speed of an actuator's stem. On the horizontal axis, time is measured in seconds. The vertical axis indicates position:

• 0: Retracted position
• 1: Extended position

Force Developed by a Cylinder

In fluid power systems, the pressure within a cylinder is transformed into force, which is then used to move a load. The relationship between force, pressure, and area is given by the following formula:

F = P * S

Where:

• F: Force (in Newtons)
• P: Pressure (in bar)
• S: Area (in cm²)

Types of Fluid Power Circuits

The most commonly employed cylinder types in circuits are Single-Acting (SA) and Double-Acting (DA) cylinders.

Circuits with Single-Acting (SA) Cylinders

Single-acting cylinders are utilized in circuits where force is only required during the extension phase. Retraction is typically achieved by a return spring or the weight of the supported load, eliminating the need for pressurized fluid to return the piston.

Circuits with Double-Acting (DA) Cylinders

Double-acting cylinders are the most widely used type. They are capable of exerting force in both the extension and retraction strokes, providing controlled movement in both directions.

End-of-Stroke Circuits

End-of-stroke circuits are essential in both pneumatic and hydraulic systems. Their primary purpose is to actuate control valves, thereby automating the circuit's operation. Common components used for end-of-stroke detection include:

• 3/2 Roller-Actuated Valves (mechanical sensors)
• Magnetic Proximity Sensors (electrical sensors)

Vehicle Fluid Power Systems

Pneumatic and hydraulic circuits integrated into vehicles can be managed electronically and electrically, enhancing their efficiency and control.

Pneumatic Engine Brake Circuit

In commercial vehicles, engine braking is achieved by closing a butterfly valve strategically placed in the exhaust manifold. This creates back pressure, slowing the vehicle.

Hydraulic Steering Circuit

For hydraulic steering circuits, electronic management is typically not available. Their operation and control are carried out purely through hydraulic and mechanical means, ensuring reliable steering response.

Electronically Managed Pneumatic Circuits

These advanced pneumatic circuits control pumps through various sensors. These sensors provide data that activates the ECU (Electronic Control Unit), which then precisely manages the pneumatic system's functions.

Electronically Managed Hydraulic Circuits

The operation of these hydraulic circuits relies on reversing the rotation of the hydraulic pump. This innovative design allows the pump to feed two separate circuits without requiring a dedicated control valve. Overpressure protection is provided by a relief valve, and fluid efficiently returns to the reservoir.

Hydraulic Circuit with Detachable Stabilizer Bar

This sophisticated system incorporates a series of sensors that continuously calculate the degree of vehicle body roll. Based on this data, the system determines the appropriate adjustment for the stabilizer bar in real-time.

• On-Road Performance: On paved roads, the system firmly holds the vehicle body, providing enhanced stability and reduced body roll during cornering.
• Off-Road Performance: In off-road conditions, particularly when selecting a drive program for rocky terrain, the stabilizer bar is automatically decoupled. This allows the wheels to remain closer to the ground, optimizing suspension travel and achieving superior traction over uneven surfaces.