Basic Pneumatics. Module 2: Direct Control of single acting cylinder PREPARED BY. IAT Curriculum Unit. January 2011

Transcription

1 Basic Pneumatics Module 2: Direct Control of single acting cylinder PREPARED BY IAT Curriculum Unit January 2011 Institute of Applied Technology, 20011

2 Module 2: Direct Control of single acting cylinder Module Objectives At the end of this module the student will be able to: 1. Deal with the different types of valve actuators. 2. Control of single acting cylinder with 3/2 way valve normally close 3. Control of single acting cylinder with 3/2 way valve normally open 4. Draw pneumatic circuit diagram. 5. Construct a pneumatic circuit according to the requirements 6. Simulate pneumatic circuit using Fluid SIM software. 2 Module 2: Direct control of single acting cylinder

3 Module Contents 1 Introduction Single acting cylinder /2 way diectional control valve /2 way valve Normally closed /2 way valve Normally open Valve actuation Manual actuation Mechanical actuation Electrical actuation Pneumatic actuation Practical Task -1...Error! Bookmark not defined Procedure of solution Simulation Assembling the circuit Practical Task -2...Error! Bookmark not defined Learning objectives Problem description Requirements Solution...Error! Bookmark not defined Solution description References...13 Module 2: Direct control of single acting cylinder 3

4 1 Introduction: As mentioned in module 1, the pneumatic system consists of the following main parts: 1- Air compressor 2- Pneumatic control valves o Directional control valves o Pressure control valves o Flow control valve 3- Pneumatic actuators o Single acting cylinders o Double acting cylinders o Motors In this module, you will learn how to control the operation of the single sting cylinder through certain directional control valves. 4 Module 2: Direct control of single acting cylinder

5 2 Single acting cylinder Single acting cylinder is an output device. The function of the SAC is to convert the pressure energy to a mechanical energy (linear motion). In single acting cylinder, the forward stroke is achieved by the compressed air, while the backward stroke is achieved by the spring. Thus the single acting cylinder produces the work in only one direction (forward stroke). Figure (2.1.a) shows the picture of the single acting cylinder. Figure (2.1.b) shows the ISO symbol of the single acting cylinder (a) Single acting cylinder (b) ISO symbol of Single acting cylinder. Figure /2 way directional control valve 3.1 3/2 way directional control valve - Normally Closed (NC) Way of operation: A 3/2-way valve has 3 ports (1, 2 and 3) and 2 switching positions (before operating and after operating). It s represented by the normal position. Normally closed means that compressed air cannot flow through the valve as shown in figure (2.2.a). When the pushbutton is actuated the valve is opened, thus allowing the air to flow from port (1) to port (2) (a) pressure port (1) is blocked Figure 2.2 Module 2: Direct control of single acting cylinder 5

6 Un-actuated In normally closed 3/2 way valve, a springloaded disk seal blocks the air flow from the air supply port (1) to the working port (2). The working port (2) is connected with exhaust port (3) as shown in Figure (2.3.a). Actuated Actuating this valve results in allowing the flow from port (1) to port (2) and blocking the exhaust port (3) as shown in figure (5.2.b) Figure (2.3.c) shows the ISO symbol of 3/2 way valve normally closed (N/C) and spring reset Advantages Switching without overlap Larger flow cross-section with shorter actuation stroke Insensitive to dirt Long service life (a) 3/2 way directional control valve NC (before actuation) (b) 3/2 way directional control valve NC (after actuation) Note: you may visit the below link for some nice animation about 3/2 normally closed valve (c) ISO symbol of 3/2 way directional control valve NC Figure Module 2: Direct control of single acting cylinder

7 3.2 3/2-Way Valve - Normally Open Position Way of operation: A 3/2-way valve has 3 ports (1, 2 and 3) and 2 switching positions (before operating and after operating). It s represented by the normal position. Normally open which means that compressed air flows through the valve as shown in figure (3.2.a). When the pushbutton is actuated the valve is closed, thus stopping the air to flow from port (1) to port (2) Un-actuated In normally closed 3/2 way valve, a spring loaded disk blocks exhaust port (3). The air supply port (1) is connected to the working port (2) Actuated Actuating this valve results in allowing the flow from port (2) to port (3) and blocking the supply air port (1) (a) 3/2 way directional control valve NO Figure (2.4.b) shows the ISO symbol of 3/2 way valve normally open (N/O) and spring reset Advantages Switching without overlap Larger flow cross-section with shorter actuation stroke Insensitive to dirt Long service life (b) ISO symbol of 3/2 way directional control valve NC Figure 2.4 Module 2: Direct control of single acting cylinder 7

8 4 Valve actuators: The pneumatic directional control valves can be actuated (operated) in several ways such as follows: 4.1 Manual actuators Figure (2.5.a) shows (from left to right) three manual actuation methods: manual, push button and foot pedal 4.2 Mechanical actuators Figure (2.5.b) shows (from left to right) two mechanical actuation methods: roller and idle return roller. (a) Manual actuation (b) Mechanical actuation 4.3 Electrical actuators Figure (2.5.c) shows an example of electrical actuation (solenoid valve) (c) Electrical actuators 4.4 Pneumatic actuators Figure (2.5.d) shows an example of pneumatic (pressure) actuation (d) Pneumatic actuation Figure Module 2: Direct control of single acting cylinder

9 5 Practical Task 2: Operating single acting cylinder Controlling the operation of the single acting cylinder by using 3/2 way valve manual actuated, spring reset and N/C. Required components: Single acting cylinder 3/2 way valve - push button - spring reset - N/C Pressure supply The pneumatic circuit diagram is shown in Fig Procedure of solution 5.2 Simulation Fig.2.6 Pneumatic circuit diagram Build the circuit on your computer using the fluidsim software and run the simulation. Write down your observations. Module 2: Direct control of single acting cylinder 9

10 5.3 Assembling the circuit 1- Prepare the components according to the above components list. 2- Mount all components according to the pneumatic circuit. 3- Connect pneumatic tubes according to the pneumatic circuit. 4- Check that all parts are connected properly and firmly with each other. 5- make sure that the supply air pressure is set to five (5) bar 6- Switch on the service unit. 7- Start the circuit. 8- Check the operation of the circuit by actuating 3/2 way valve 9-Troubleshoot the circuit for any malfunctions 10- Turn off the service unit 11- Dismantle and tidy up. 12- Write down your observation. 10 Module 2: Direct control of single acting cylinder

11 6 Practical Task 2: Opening fodder silo 6.1 Learning objectives: After completing this task you will be: Familiar with the set-up and mode of operation of a normally open 3/2- way valve. Able to recognize and sketch the various types of actuation of directional control valves. Able to explain and set up direct actuation. 6.2 problems Description: The slide of a fodder silo is to be opened by pressing a pushbutton. When the pushbutton is released, the slide is closed once again as shown in figure 2.7 below. Figure (2.7) Postional schetch 6.3 Requirements: 1. Draw pneumatic circuit diagram using the space provided below 2. Simulate the circuit using FluidSim software. 3. Assemble the circuit practically and check its operation. 4. Write down your observation below Module 2: Direct control of single acting cylinder 11

12 Draw the pneumatic circuit here 12 Module 2: Direct control of single acting cylinder

13 References: 1- Festo manuals and workbook TP www. Fest-didactic.com Module 2: Direct control of single acting cylinder 13

14 Student s notes 14 Module 2: Direct control of single acting cylinder

15 Worksheet 1 Define the single acting cylinder and draw its symbol. What is the function of the 3/2 way valve push button normally closed?.. What is the function of the 3/2 way valve push button normally open? Draw ISO symbols of 3/2 way valve push button, spring return NO and NC. Name the following valve and recognize what is the type of actuator Module 2: Direct control of single acting cylinder 15

16 Worksheet 2 Draw the ISO symbol for the following: 1- Manual valve actuator... 2-Mechanical valve actuator... 3-Pneumatic valve actuator... 4-Electrical valve actuator Module 2: Direct control of single acting cylinder