Basic Pneumatics. Module 9: Time delay valve. Academic Services PREPARED BY. April 2012

Transcription

1 Basic Pneumatics PREPARED BY Academic Services April 2012 Applied Technology High Schools, 2012

2 Module Objectives After the completion of this module, the student will be able to: Demonstrate an understanding of the different types of time delay valves. Identify the normally closed time delay valve. Identify the main parts of the time delay valve. Draw a pneumatic circuit diagram that consists of a time delay valve, normally closed. Simulate pneumatic circuit that consists of a time delay valve using Fluid SIM software. Build a pneumatic circuit that consists of a time delay valve as per specific requirements. Module Contents Topic Page No. 1 Function and symbol 3 2 Design 4 3 Principle of operation 5 4 Time behavior 6 5 Practical task 1 (Pressing device) 7 6 Worksheet 11

3 1. Time Delay Valve Pneumatic time elements can be formed very simply from combinations of three valves: directional control valve, throttle valve and reservoirs. 1.1 Function Time delay valve is used to delay the output signal. The time delay valve is actuated by a pneumatic signal through the tank after a preset time delay has elapsed. The returned to the normal position via return spring when the signal is terminated. Fig. (9.1) shows the picture of the time delay valve, normally closed. N/C time delay valve Fig Symbols Fig. (9.2.a) shows the ISO symbol of normally closed time delay valve. (a) ISO symbol of N/C time delay valve Fig. (9.2.b) shows the ISO symbol of normally opened time delay valve. (b) ISO symbol of N/O time delay valve Fig. 9.2

4 2. Design The time delay valve is a combination of a 3/2 way valve, one way flow control valve and air reservoir. The 3/2 way valve can be normally open or normally closed. The delay time is generally ranging between (0-300) seconds for both types of valves (normally opened and normally closed). By using additional reservoirs, the delaying time can be extended. Fig. 9.3 Fig. (9.3) shows the parts of the time delay valve, normally closed. The type of the time delay valve whether normally opened or normally closed is determined according to the type of the 3/2 way valve if it is N/O or N/C. Fig. (9.4) shows the two types of 3/2 way valve. (N/C) and (N/O). Fig. 9.4.a 3/2 way valve (N/C) Fig. 9.4.a 3/2 way valve (N/O) Fig. 9.4

5 3. Principle of operation The following operational principle applies for a time delay valve in normally closed position as shown in Fig. (9.5.a). The compressed air is supplied to the valve at connection 1. The control air flows into the valve at 12 through a one way flow control valve and depending on the setting of the throttling screw, a greater or lesser amount of air flows per unit of time into the air reservoir, when the necessary control pressure has built up in the air reservoir, the pilot control of the 3/2 way valve is moved downwards. This blocks the passage from 2 to 3. The valve disc is lifted from its seat and thus air can flow from1 to 2 as shown in Fig. (9.5.b). The time required for pressure to build up in the air reservoir is equal to the control time of the valve. (a) (b) Un-actuated position Actuated position Fig. 9.5

6 4. Time behavior of circuits with time delay valves. The time response and behavior of the pneumatic circuits with time delay valves varies according to the following two factors: 1- Type of 3/2 way valve if it is N/O or N/C. 2- The direction of the check valve in the one way flow control valve. (Direction of throttling). Fig. 9.6 shows the most four important cases. Fig. 9.6: Time delay with delay on and off

7 5. Practical Task 1: Pressing device with time control 5.1 Learning objectives: Upon the completion of this task, the student will be Familiar with the set-up and mode of operation of a time delay valve normally closed. Able to recognize and sketch the time delay valve. Able to choose different pneumatic components according to the given conditions. 5.2 Problem Description: A double acting cylinder is used to press glued components together. Upon operation of a push button, the clamping cylinder extends as shown in the Fig. 9.7 below. Once the fully advanced position is reached, the cylinder is to remain for a time of T = 6 seconds and then retract to the initial position automatically. The cylinder retraction is to be adjustable. A new start cycle is only possible after the cylinder has fully retracted. Fig. 9.7 Postional schetch

8 5.3 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. Draw the pneumatic circuit here.

9 6. For further reading, you can use the following links: Supplementary recourses 1. Pneumatics video from Festo. 2. FluidSIM software. 8. References 1- Festo manuals and workbook TP Festo manuals and textbook TP101 ATM 1132 Basic Pneumatics

10 Student s notes

11 Worksheet 1 Draw the symbol of time delay valve, normally closed Draw the symbol of 3/2 way, roller lever valve Draw the symbol of 5/2 way, double pilot valve What is the function of time delay valve? What are the three parts consisting the time delay valve?

12 Work sheet 2 A rod of a double acting cylinder is advanced by pressing a push button valve, after reaching the end position; it stays 5 seconds and then returns automatically to the initial position. Draw the required circuit diagram.....