Pneumatic Systems PDF

CHAPTER 2 FINAL ELEMENT Chapter 3: Final Elements Final element - is a device that receives a control signal and regulates the amount of material or energy in a process. Control Valves: - manipulate the flow of utilities (such as steam, air, water), - an inline device in a flow stream...

CHAPTER 2 FINAL ELEMENT Chapter 3: Final Elements Final element - is a device that receives a control signal and regulates the amount of material or energy in a process. Control Valves: - manipulate the flow of utilities (such as steam, air, water), - an inline device in a flow stream that receives command from a controller and manipulates the flow of a gas or fluid in one of three ways: 1. Interrupt flow (shut-off service) Control valves for flow shut-off service have two positions. In the open position, flow is allowed to exit the valve. In the closed position, flow is blocked from exiting the valve. 2. Divert flow to another path in the system (divert service) Control Valves for divert service also have two positions however, flow is never blocked. In the one position, flow is allowed from the common port A. In the other position, flow is allowed form the common port to port B 3. Regulate the rate of flow (throttling service) Control valves for throttling service have many positions. The position of the valve determines the rate of flow allowed through the valve. INSTRUMENT VALVES (6 major valve types) 1. Gate Valves are used for full on and off service 2. Globe Valves sometime referred to as an S valve are mostly for throttling service 3. Check Valves are designed to prevent backflow. The three basic types of check valves are the swing and lift. 4. Ball valves do not require lubrication and are quick open and quick off. 5. Plug Valves have evolved from a tapered plug in a bamboo line to modern versions such as the figure below. Lubrication not only ensures the ease of operation, but acts to ensure the tight sealing and resistance to corrosive solutions. 6. Butterfly Valves is the most popular throttling device REGULATORS Regulators - commonly used to control water pressure in a distribution system that must be held to a value that ensures supply to all sectors of the system. Pressure Regulator - an adjustable valve that is designed to automatically control the pressure downstream of the regulator. Spring-loaded pressure regulator - a regulator consisting of a throttling element such as a valve plug connected to a pressure sensing diaphragm ACTUATORS Actuators - are pneumatic, electrical or hydraulic devices that provide the force and motion to open and close a valve. Spring-return actuator - a piston or diaphragm actuator with an internal spring to force the actuator shaft to one end of its travel. DIRECTS-ACTING VALVES (SOLENOIDS) Direct-acting valves - the simplest form of ON/OFF valves. For example: a two-way solenoid valve can be used to directly control the flow of a process fluid. CHAPTER 4.1 INTRODUCTION TO PNEUMATICS PNEUMATICS AUTOMATION PRINCIPLES CHARACTERISTICS AND APPLICATIONS OF PNEUMATICS Pneumatics - Utilisation of compressed air in science and industry in order to perform mechanical work and control Pneumatic System - a system that uses compressed air to transmit and control energy. The advantages of pneumatic systems: 1. High effectiveness Many factories have equipped their production lines with compressed air supplies and movable compressors. 2. High durability and reliability Pneumatic components are extremely durable and cannot be damaged easily. 3. Simple design The designs of pneumatic components are relatively simple. 4. High adaptability to harsh environment Compared to the elements of other systems, compressed air is less affected by high temperature, dust, corrosion, etc. 5. Safety Pneumatic systems are safer than electromotive systems because they can work in inflammable environment without causing fire or explosion. 6. Easy selection of speed and pressure The operation of pneumatic systems does not produce pollutants. The air released is also processed in special ways. 7. Economical As pneumatic components are not expensive, the costs of pneumatic systems are quite low. Limitations of pneumatic systems 1. Relatively low accuracy As pneumatic systems are powered by the force provided by compressed air, their operation is subject to the volume of the compressed air. 2. Low loading As the cylinders of pneumatic components are not very large, a pneumatic system cannot drive loads that are too heavy. 3. Processing required before use Compressed air must be processed before use to ensure the absence of water vapor or dust. Otherwise, the moving parts of the pneumatic components may wear out quickly due to friction. 4. Uneven moving speed As air can easily be compressed, the moving speeds of the pistons are relatively uneven. 5. Noise Noise will be produced when compressed air is released from the pneumatic components. Pneumatic Components can perform the following types of motion: (Linear, Swivel and Rotary) Structure and signal flow of pneumatic systems Pneumatic systems consist of interconnection of different groups of elements: The primary levels in a pneumatic system are: Energy Supply Input elements (sensors) Processing Elements (processor) Control Elements Power Components (actuators) Chapter 4.2 Air Service Unit and Directional Valves PRODUCTION AND TRANSPORTATION OF COMPRESSED AIR Compressor - can compress air to the required pressures. Compressors can be divided into two classes: reciprocator and rotary. Pressure regulating components are formed by various components, each of which has its own pneumatic symbol: Filter – can remove impurities from compressed air before it is fed to the pneumatic components. Pressure regulator – to stabilise the pressure and regulate the operation of pneumatic components Lubricator – To provide lubrication for pneumatic components Air Service Unit. - can fulfil the following: preparation, filtering and lubricating VALVES The function of valves is to control the pressure or flow rate of pressure media. Depending on design, these can be divided into the following categories: Directional Control Valves o Input/Signalling Valves o Processing Valves o Control Elements  Non-return Valves Flow Control Valves Pressure Control Valves Shut-off Valves DIRECTIONAL VALVES Directional control valves - are used as Control elements, Processing elements or Input elements THE VALVE IS DESCRIBED BY: The number of ports or openings (ways): 2-way, 3 way Numbers of positions: 2 position, 3 position Methods of actuations of the valve: manually or mechanically actuated Methods of return actuation: spring return, air return Signalling Element the directional control valve is operated by a roller lever to detect the piston rod position of a cylinder. Processing Element - the directional control valve redirects or cancels signal depending on the signal inputs received