ASI CIE 2

Principles of Pneumatic Control

(a) Pneumatic Circuit

  • Pneumatic control systems can be designed as pneumatic circuits which consist of various pneumatic components.

  • Components include:

    • Cylinders: Provide motion by compressing air.

    • Directional Control Valves: Control the direction of air flow.

    • Flow Control Valves: Manage the rate of flow of the air.

  • Functions of pneumatic circuits:

    • To control the injection and release of compressed air in the cylinders.

    • To use one valve to control another valve.

Principles of Pneumatic Control

(b) Pneumatic Circuit Diagram

  • A pneumatic circuit diagram utilizes symbols to represent its design.

  • Basic rules for drawing pneumatic diagrams:

    • The diagram represents the circuit in static form, assuming no pressure supply.

    • The placement of components follows the same assumption.

Principles of Pneumatic Control

(b) Pneumatic Circuit Diagram

  • Directional Control Valve Symbols:

    • Represented by squares; each function of the valve is shown with a square.

    • The inlet and exhaust are at the bottom; the outlet is at the top.

    • Airflow direction is indicated by arrows (↓).

    • A disconnected external port is represented by the symbol “┬”.

  • Special symbols:

    • “ ” for air input.

    • “ ” for exhaust.

Principles of Pneumatic Control

3/2 Directional Control Valve

  • Used to control a single-acting cylinder.

  • Operation:

    • Open valves connect 'P' to 'A' and close until 'P' and 'A' connect.

    • Then another valve opens the seal between 'A' and 'R' (exhaust).

  • Types:

    • Normally Closed (N.C.)

    • Normally Open (N.O.)

Circuit Function of 3-Way Air Valves

  • A 3/2-way pneumatic valve has three connection ports and two states:

    • Ports:

      • Inlet ('P', 1)

      • Outlet ('A', 2)

      • Exhaust ('R', 3)

    • States:

      • Open: Air flows from inlet to outlet.

      • Closed: Air flows from outlet to exhaust.

  • Types:

    • Normally Closed (NC) when not actuated.

    • Normally Open (NO) when not actuated.

3/2-Way Pneumatic Solenoid Valve - Main Components

  • Components of the valve:

    • Manual Operator (A): For manual control.

    • Fixed Core (B): Stationary magnetic core.

    • Solenoid (C): Moves the armature.

    • Armature (D): Moves in response to magnetic field.

    • Push Pin (E): Transfers armature movement to the spool.

    • Return Sprung (F): Resets armature position.

    • Spool (G): Manages the air flow.

    • Atmosphere (H): Exhaust port.

    • Valve Output (I): Outlet port for exiting media.

    • Air Supply (J): Entry port for compressed air.

    • Return Spring 2 (K): Aids in spool return.

    • Orifice (L): Opening for airflow within the valve.

Working of 3/2-Way Pneumatic Solenoid Valve

  • When energized, solenoid (C) produces a magnetic field moving the armature (D).

  • Armature movement via push pin (E) shifts spool (G) to control orifice (L).

  • Flow from air supply (J) is allowed through valve output (I).

  • When de-energized, return springs (F) and (K) reset the armature and spool, halting air flow and exhausting remaining air to the atmosphere (H).

5/2 Directional Control Valve

  • Contains five ports with two position states.

  • Directs airflow into one port, exhausting from another while maintaining motion.

  • Port designations:

    • Using Numbers/Letters:

      • E.g., Supply air port (1), outlet ports (2, 4), exhaust ports (3, 5).

  • Common across various manufacturers but may differ in designation.

Circuit Functions of 5/2 Directional Control Valve

  • When a pressure pulse is input into 'P', the spool shifts connecting 'P' with 'B'.

  • 'A' releases excess air through exhaust ports 'R1', 'R2'.

  • Operates in a memory function until contrary signals are received.

Aircraft Pneumatic Systems - Control Valves

  • Control valves regulate air flow, types include:

    • Non-return Valves: Prevent backflow.

    • Flow Control Valves: Maintain desired flow rates.

    • Shuttle Valves: Switches between input sources.

Shuttle Valves

  • Serve as double control or single control non-return valves.

  • Features two air inlets ('P1', 'P2') and one outlet ('A').

  • Air enters 'P1' sealing 'P2' and vice versa, regulating flow.

Setting Circuit Diagrams

  • Components should be spread to express the circuit clearly and organized by:

    • Power Level

    • Logic Level

    • Signal Input Level

Basic Principles of Drawing Pneumatic Circuit Diagrams

  • Manual switch (1) must not be activated.

  • Air pressure is maintained along the circuit line (3).

  • Piston rod operates under pressure indicated in cylinder cavity (4).

  • Air is released from the exhaust connection (5).

Memory Function

  • Memory allows components to maintain states until signals change.

  • Output stayed ON until momentary control activation replaces signal.

Single Acting Cylinder Control

  • Control can be achieved manually or through multiple valves (Logic Control).

  • Utilizing a 3/2 directional control valve, activating causes cylinder movement.

  • Speed control is managed by restricting air flow and utilizing a one-way flow control valve.

OR Function

  • Manual operation or automated circuit signals can control a single acting cylinder.

  • Function is depicted when two 3/2 directional control valves are connected.

AND Function

  • Interlock control requires two conditions to be satisfied for operation.

  • Example includes a safety door that must be closed alongside valve activation.

Double Acting Cylinder

  • Control typically employs a 5/2 DCV.

  • Outlets connect as necessary for fluid movement based on control actions.

  • Flow control valves aid in adjusting both directions, maintaining operational stability.

Conclusion

  • The detailed examination of pneumatic system principles including their components, operation, and diagrams provide vital knowledge for understanding and designing pneumatic control systems.