Uma Devi Nadarajah Pneumatic Circuit Design
Uma Devi Nadarajah Pneumatic Circuit Design by Uma Devi Nadarajah Mechanical Engineering Department Politeknik Banting Selangor https://pbs.mypolycc.edu.my 1 st Edition 2022
Declaration Pneumatic Circuit Design All right reserved. No part of this publication may be reproduced or transmitted in any form or by any electronic or mechanical including photocopy, recording, or any information storage and retrieval system without permission from Politeknik Banting Selangor and Bahagian Instruksional dan Pembelajaran Digital JPPKK. Author Uma Devi Nadarajah Editor Zalaida Binti Talib 1 st Published 2022 Published by: Politeknik Banting Selangor, Persiaran Ilmu, Jalan Sultan Abdul Samad, 42700 Banting, Selangor Darul Ehsan. Telephone : 03-3120 1657 / 03-3120 1625 Fax: 03-3120 1706 Website : https://pbs.mypolycc.edu.my/ E-mel : [email protected] PNEUMATIC CIRCUIT DESIGN i
Thank you ACKNOWLEDGEMENT Uma Devi Nadarajah We would like to thank Politeknik Banting Selangor for providing us with the wonderful opportunity to write this e-book. We would like to thank everyone who gave us the opportunity to discover the hidden talent within us to become authors, which may have been hidden deep within us and unknown to the rest of the world. We are grateful to the PBS e-Learning Unit for consistently sharing knowledge on e-book writing, encouraging us, and being our companion in e-book writing discussions. We would like to thank our colleagues, contributors, and information source authors who have directly or indirectly inspired us to complete this e-book. A special thanks to our cherished family for their unwavering support and for allowing us the time to write this e-book. Last but not least, we want to thank God for keeping us positive and hopeful while we were writing this e-book. ii
PREFACE Uma Devi Nadarajah This ebook was written as part of an e-learning activity and to improve digital learning, which is useful during any outbreak in addition to supporting the Go Green initiative; going paperless. This ebook explains the fundamentals of pneumatic circuit design for both types of linear actuators using various types of pneumatic valves. By providing examples for each subtopic, this ebook was created to help polytechnic students better understand pneumatic circuit design. The steps for developing multiple cylinder circuits have been shown in detail and thoroughly explained with examples of the questions. This topic was chosen because students frequently struggle with designing circuits when asked questions in class. The benefit of using this book is that it includes plenty of exercises and answers for each question, allowing students to practise the questions during the lesson and use them as a revision for their exam or even as a reference while working or studying. Almost all the circuits in the examples of this ebook have been included in its simulation video using Automation Studio 6.1 Educational Edition software to help students understand how a pneumatic circuit works. This would improve understanding and learning experience, especially for students who use this book for self-study or revision. This interactive e-book would appeal to Y-generation students who prefer to use technology for teaching and learning rather than traditional book formats. iiI
TABLE OF CONTENT PNEUMATIC CIRCUIT DESIGN POLITEKNIK BANTING SELANGOR Content Page Number iv Declaration i Acknowledgement ii Preface iii Table of content iv Introduction 1 Direct method control 2 Indirect method control 5 Pneumatic Circuit Design for One Cylinder – AND valve 7 Pneumatic Circuit Design for One Cylinder – OR valve 8 Pneumatic Circuit Design for One Cylinder – 3/2-way and 5/2-way valves with single and double pilot DCV 9 Pneumatic Circuit Design for One Cylinder – One-way flow control valve 10 Pneumatic Circuit Design for One Cylinder – Pressure sequence valve 11 Pneumatic Circuit Design for One Cylinder – Time delay valve 12 Development of Multiple Cylinder Circuits 14 Classic method 14 Elimination of signal conflict 22 Cascade method 24 Pneumatic circuit design - Tutorial 30 Answers 34 References 42
PNEUMATIC CIRCUIT DESIGN POLITEKNIK BANTING SELANGOR PNEUMATIC CIRCUIT DESIGN Introduction 1. Pneumatic control systems can be designed in the form of pneumatic circuits. 2. A pneumatic circuit is formed by various pneumatic components, such as cylinders, directional control valves, flow control valves, pressure regulators, signal processing elements such as shuttle valves, two-pressure vales etc. 3. Pneumatic circuits have the following functions: To control the entry and exit of compressed air in the cylinders. To use one valve to control another valve To control actuators or any other pneumatic devices. Movement of the Cylinder In this section, we will learn the basic circuit for one cylinder based on a. Direct method for single acting and double acting cylinder b. Indirect method for single acting and double acting cylinder PNEUMATIC CIRCUIT DESIGN 4. To be able to design pneumatic circuits, one should have basic knowledge of designing simple pneumatic circuits. With this foundation, one would be able to move on to designing more complicated circuits involving many more cylinders. 1
PNEUMATIC CIRCUIT DESIGN a. Single-acting Cylinder Control 1. Pneumatic cylinder can be directly controlled by the actuation of the final directional control valve as shown in figure 1. These valves can be controlled manually or mechanically. 2. This circuit can be used for small cylinders and cylinders operating at low speeds with less flow rate requirements. 3. When the directional control valve is actuated by the push button, the valve switches over to the open position, communicating the working source to the cylinder volume. This results in the forward motion of the piston. 4. When the push button is released, the reset spring of the valve restores the valve to the initial position [closed]. 5. The cylinder space is connected to the exhaust port thereby piston retracts either due to spring or supply pressure applied from the other port. Note: When drawing a schematic circuit, draw the circuit in the initial / retract position only. Example 1: Draw a pneumatic circuit for the following pneumatic punching machine. Figure 2.: Pneumatic punching machine i. Direct Method Control 1. A direct control signal is used in the simplest level of control for a single or double-acting cylinder. This method directs cylinder actuation through a manually or mechanically actuated valve, with no intermediate switching of the additional directional control valve. POLITEKNIK BANTING SELANGOR Initial / retracting Extending Figure 1: Direct control of a single-acting cylinder 2 Solution Figure 3: Pneumatic clamping machine
A small single-acting cylinder has to extend and clamp a workpiece when a push button is pressed as shown in Figure 4. As long as the push button is activated, the cylinder should remain in the clamped position. If the push button, S1 is released, the clamp is to retract. The power source for S1 is obtained from an additional push button, S2. Draw the pneumatic circuit. Example 2: Draw a pneumatic circuit for the following pneumatic application PNEUMATIC CIRCUIT DESIGN Figure 5: Solution for Example 2 3 POLITEKNIK BANTING SELANGOR Figure 4: Pneumatic clamping machine Solution b. Double-acting Cylinder Control 1. The only difference between a single-acting cylinder and a double-acting cylinder is that a double-acting cylinder uses a 5/2 directional control valve instead of a 3/2 directional control valve (figure 6). 2. Figure 6 shows the direct control of a double-acting cylinder. In this circuit, whenever the operation button is pushed manually, the double-acting cylinder will move back and forth once. Figure 6: Direct control of a doubleacting cylinder
PNEUMATIC CIRCUIT DESIGN Example 3: Draw a pneumatic circuit for the following question using direct method. Figure 7.: Pneumatic punching machine A pneumatic system is to be designed to operate the door of public transport vehicles. (Figure 7). Assuming that the opening and closing of the doors are controlled by two push button switches ON and OFF. When the push button switch ON is pressed, the door will open. When the push button switch OFF is pushed, the door will close. 4 POLITEKNIK BANTING SELANGOR Solution Figure 8: Solution for Example 3 Note: Door open (ON): Cylinder extends Door closed (OFF): Cylinder retracts Explanation for circuit in Figure 8: When the push button ON is pressed, the compressed air will flow from port 1 to port 2, thus the cylinder retracts and the door is open. To close the door, the cylinder has to extend. This could be done by pressing the push button OFF where the compressed air will flow from port 1 to port 2 and cause the cylinder to extend.
PNEUMATIC CIRCUIT DESIGN ii. Indirect Method a. Single-acting Cylinder control 1. This type of circuit (figure 9) is suitable for large double-acting cylinders as well as cylinders operating at high speeds. 2. The final pilot control valve is actuated by a normally closed 3/2 push button operated valve. The final control valves handle a large quantity of air. 3. When the push button is pressed, the 3/2- way normally closed valve generates a pilot signal 12 which controls the final valve thereby connecting the working medium to the piston side of the cylinder to advance the cylinder. Figure 9: Indirect control of single acting cylinder 4. When the push button is released, pilot air from the final valve is vented to the atmosphere through 3/2 NC – DCV. 5. The signal pressure required can be around 1-1.5 bar. The working pressure passing through the final control valve depends on the force requirement which will be around 4-6 bar. 6. Indirect control permits the processing of input signals. Single piloted valves are rarely used in applications where the piston has to retract immediately after taking out the set pilot signal. 5 POLITEKNIK BANTING SELANGOR 3 1 2 2 1 3 air service unit single-acting cylinder 3/2-way NC single pilot DCV, spring return Indirect method for single acting cylinder
Figure 10: Indirect control of double-acting cylinder using 5/2-way double pilot DCV PNEUMATIC CIRCUIT DESIGN b. Double-acting Cylinder control 1. This type of circuit (figure 10) is using 5/2- way double pilot DCV to control the movement of the cylinder. 2. The pilot 14 and 12 of the 5/2-way DCV are actuated by the normally closed 3/2- way push button operated DCV, S1 and S2. The final control valves handle a large quantity of air. 3. When the push button DCV, S1 is pressed, the 3/2-way normally closed valve generates an output signal which is connected to pilot signal 14. This signal actuates the 5/2-way double pilot DCV, connecting the working medium to the piston side of the cylinder to advance the cylinder. 5. When the S1 push button is released, the 5/2- way DCV remain in actuated position until a signal presents at pilot 12 of the DCV. 6. The double-acting cylinder retracts when the S2 push button is pressed. The output of S2 generates signals at pilot 12 of the 5/2-way double pilot DCV. Thus the DCV is deactuated and back to its initial position (i.e. right control box). This makes the compressed air to the rod side and the cylinder retracts. 7. The signal pressure required can be around 1- 1.5 bar. The working pressure passing through the final control valve depends on the force requirement which will be around 4-6 bar. 8. Indirect control permits the processing of input signals. Single piloted valves are rarely used in applications where the piston has to retract immediately after taking out the set pilot signal. 6 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN a. Circuit using dual pressure valve (AND function) 1. This valve is the pneumatic AND valve. It is a derivation from the non-return valve. 2. A two-pressure valve requires two pressurised inputs to allow output from itself. 3. Figure 11 shows the working principle of this valve. It has two inputs; X and Y and one output 2. When the compressed air is applied to either X or input Y, the spool moves to block the flow, and no signal appears at output 2. 4. If signals are applied to both inputs X and y, the compressed air flows through the valve, and the signal appears at the output. 5. AND function is also known as interlock control which means control is possible only when two conditions are satisfied. 6. A classic example is a pneumatic system that works only when its safety door is closed and its manual control valve is operated. The flow passage will open only when both control valves are operated. POLITEKNIK BANTING SELANGOR Figure 11: Working principle of AND valve (Image sources: Virtual Labs) Pneumatic Circuit Design for One Cylinder In this subtopic, we will learn how to construct pneumatic circuits for one cylinder using the following valves: a. Dual pressure valve (AND function) b. Shuttle valve (OR function) c. 3/2-way and 5/2-way valves with single and double pilot DCV d. One-way flow control valve e. Pressure sequence valve f. Time delay valve 7 X Y X Y 2 2 2
PNEUMATIC CIRCUIT DESIGN Figure 12: Control of a single-acting cylinder using AND valve 7. Figure 12 shows the circuit diagram of an AND function circuit. The cylinder will work only when both pushbuttons valves are operated. Exercise 2: A double-acting cylinder is to advance if two pushbuttons are pressed. The cylinder will retract if one of the pushbuttons is released. Draw the pneumatic circuit. 1. Shuttle valve is a three-ported valve which has two inlets and one outlet. When compressed air enters port P1, the poppet will be pushed to port P2 and it is blocked, thus compressed air flows from port P1 to port A. Refer to figure 13 for the working principle of the shuttle valve. 2. This valve is also called an OR valve because port A is able to produce output if the compressed air is applied to either port P1 or P2. 3. A shuttle valve may be used, when the cylinder or valve is to be actuated from two points, which may be remote from one another. b. Circuit using shuttle valve (OR function) Figure 13: Shuttle valve (OR valve) 8 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN POLITEKNIK BANTING SELANGOR Figure 14: Pneumatic circuit control using shuttle valve 6. The cylinder only can return if both pushbuttons S1 and S2 are released. 4. Figure 14 shows an example of a shuttle valve in a pneumatic circuit using a singleacting cylinder. This example shows that the single-acting cylinder can be operated either by manually operated 3/2-way push button DCV or mechanically operated 3/2-way roller DCV. 5. When either pushbutton S1 or S2 is pressed, an output signal will be produced at the OR valve, which causes the single-acting cylinder to extend. Exercise 3: A double-acting cylinder is to advance if one of two pushbuttons is pressed. The cylinder will retract if both pushbuttons are released. Draw the pneumatic circuit. c. Circuit using 3/2-way and 5/2-way valves with single and double pilot DCV 1. Most of the pneumatic circuits use 3/2-way or 5/2-way single and double pilot DCV to control the movement of the cylinder. 2. For a single-acting cylinder, 3/2-way single piloted will be used meanwhile, the doubleacting cylinder uses 5/2-way single or double pilot DCV. 3. The usage of 3/2-way and/or 5/2-way single or double pilot DCV is depending on the application. These directional control valves are actuated pneumatically. Exercise 4: Name the components a. d. c. b. 9 POLITEKNIK BANTING SELANGOR S1 S2
PNEUMATIC CIRCUIT DESIGN d. Circuit using one-way flow control valve 1. One-way flow control valve controls air flow only in one direction which is through the air throttle (figure15). Generally, this valve used to control speed of actuator and is installed in the working pressure line, between the final control valve and the cylinder ports. Figure 15: One-way flow control valve 2. Figure 16 shows an example of a speed control circuit for a double-acting cylinder. When the 3/2- way NC push button directional control valve, S1 is pressed, the signal presents at port 14 of the single pilot directional control valve, 1.1. Air flows to the cylinder through the one-way flow control valve. At this point, air flows choose the throttle path since the check valve does not allow airflow. The air going into the cylinder is controlled, thus the cylinder extends slowly. This flow control method is known as meter-in. Figure 16: Meter-in method Figure 17: Meter-out method 3. In figure 17, when the 3/2-way NC push button directional control valve, S1 is pressed, a signal presents at port 14 of the single pilot directional control valve, 1.1. Air flows to the cylinder without any control, however, when it comes out from the cylinder, air flows through the throttle path since the check valve does not allow the airflow. The air coming out of the cylinder is controlled, thus the cylinder extends slowly. This flow control method is known as meter-out. 10 POLITEKNIK BANTING SELANGOR Exercise 5: Identify whether the following circuit is a meter-in or meter-out method. a) b)
PNEUMATIC CIRCUIT DESIGN e. Circuit using pressure sequence valve 1. Pressure sequence valve is basically can be used when two operations are in sequence. For example, Cylinder A extends after Cylinder B. 2. Sequence valve generates a pneumatic signal if the sensing pressure (signal input) is more than the desired set pressure. 3. This generated output signal is used to control the movement of a cylinder by using it as a set signal or reset signal to the final control valve to obtain forward or return motion respectively 4. A pressure sequence valve is operated on the same principle as operating a pressure relief valve. The valve is used where a specific pressure is needed to switch the control position in the pneumatic control system. 5. Figure 18 shows the structure and the operating principle of a pressure sequence valve. The port 1, 2 and 3 basically refers to a 3/2-way NC pilot operated directional control valve. The pilot gets the signal from the pressure signal. 6. If the pressure of the compressed air applied to port 12 reaches the pressure set by a spring, the valve is operated to send an output signal to port 2 as shown in figure 19. 1 Figure 19: Actuated pressure sequence valve Image sources: Festo Figure 18: Pressure sequence valve Image sources: Festo 3 2 1 12 Screw 8. Figure 20 shows the application that uses a pressure sequence valve to check whether the cylinder completes the forward motion. 5/2-way double pilot DCV is switched by the start pushbutton allowing the cylinder in forwarding motion. Set the operating pressure of the pressure sequence valve higher than the forward pressure of the cylinder to operate the 3/2-way NC single pilot DCV (combination of pressure sequence valve) after the cylinder completes the forward motion. 9. A pressure sequence valve is less reliable than a limit switch to control the cylinder position and is only recommendable in a special setup. Figure 20: Application of pressure sequence valve 11 POLITEKNIK BANTING SELANGOR 3 2 12
PNEUMATIC CIRCUIT DESIGN f. Circuit using time delay valve 1. The purpose of a pneumatic timer is to create a time delay in signal for pilot-operated circuits. 2. A time delay valve is operated for a certain period after the control signal has been applied to control the valve. A time delay valve consists of a one-way flow control valve, a tank and a compressed air-operated 3/2-way NC valve. 3. The time delay function is obtainable by controlling the rate of flow control of the air into or from the reservoir by adjusting the one-way flow control valve. 4. There are two types of time delay valves depending on the type of the combined 3/2-way valve; a. a normally closed (NC) time delay valve and b. a normally open (NO) time delay valve. a. Normally closed (NC) time delay valve Figure 21: Symbol of NC type time delay 1. In the NC time delay valve, the compressed air control signal applied to Z enters into a tank at the pressure controlled through a one-way flow control valve. Once the pressure in the tank reaches pressure high enough to operate the valve, a 3/2-way valve is operated to allow the air to flow from P to A. 2. The output signal from A is delayed for a certain period after the control signal has been applied to Z. The delay time is generally within 30 seconds that is adjustable by controlling the flow rate of a one-way flow control valve. 3. Figure 21 shows the symbols and the operating characteristics of the NC-type time delay valve. Figure 22:Control circuit diagram with NC time delay valve 12 POLITEKNIK BANTING SELANGOR 4. The output signal is obtainable from A in a certain period ( t) after the control signal has been applied to z, and no output signal will be obtainable from A if no control signal is applied to Z. The valve is used for where a certain period of delay is needed. Z A P
PNEUMATIC CIRCUIT DESIGN b. Normally Open (NO) Time Delay Valve 1. Normally open time delay valve is operated on the same principle as operating an NC time delay valve. The only difference is that a NO time delay valve uses a NO 3/2-way valve. 2. Figure 23 shows the symbol and operating characteristics of the NO time delay valve. The valve allows the compressed air to flow from P to A. If the control signal is applied to Z, no output is obtained from A for a certain period. 3. Figure 24 shows the control circuit with NO time delay valve. Valve S1 is operated to allow a double-acting cylinder to move forward. 4. Once the cylinder reaches the forward end position and touches valve a1, the cylinder returns back immediately regardless of whether valve S1 is operated because the control signal by valve S1 for the forward motion has already been changed into a pulse signal. 5. Figure 25 shows how a NO time delay valve produces a pulse signal when a control signal is applied to Z. Figure 23: Symbol of NO type time delay Figure 25: NO time delay valve as a pulse signal Figure 24: Control circuit diagram using NO time delay valve 5. Figure 22 shows the control circuit diagram with an NC time delay valve. When the start pushbutton is pressed, it triggers the operation of valve 1.1 through the right pilot and causes the double-acting cylinder to advance. 6. When the forward motion of cylinder 1. 0 has been completed, limit switch 1.3 is actuated and sends the signal to port Z of the NC time delay valve. 7. When the signal presents at Z, the compressed air enters the tank through a one-way flow control valve in a certain period. Once the pressure in the tank reaches enough pressure to actuate the 3/2-way DCV, the output from A switches the position of valve 1.1. through the left pilot which allows the cylinder to retract. This retraction occurs after a certain period from the actuation of valve 1.3 (limit switch). 8. Once the cylinder starts the backward motion, valve 1.3 is returned to its normal position, and causes the time delay valve also returns to its normal position. 13 POLITEKNIK BANTING SELANGOR P A R Z P A R Z
PNEUMATIC CIRCUIT DESIGN Development of Multiple Cylinder Circuits 1. Multi-cylinder pneumatics circuits can be designed in various methods. There is no universal circuit design method that suits all types of circuits. Some methods are commonly used for compound circuits but would be too expensive for simple circuits. There are five common methods used by engineering and they are given below a. Classic method or Intuitive method b. Cascade method c. Step counter method d. Karnaugh–Veitch method e. Combinational circuit design 2. In this section, only two methods; the classic method and cascade method are discussed. i. Classic method or intuitive method 1. In the classic method, the circuit can be designed by use of pneumatic general knowledge following the sequence intuitively. In general, the steps are as follows: Step 1: Write down sequences and draw motion diagrams Step 2: Draw in cylinders and control valves and complete the circuit intuitively Step 3: Analyse the circuit to ensure the functionality of the circuit. 2. In most pneumatic applications, more than one cylinder is used. The movement of the cylinders is automatic and is designed in such a way as the required sequence. 3. The position of the cylinder and the resultant actuation of the final control element are determined by sensors. The type of sensor used in this method is the mechanical limit switch. 4. The movement of various cylinders can be achieved by the activation of limit switches of different cylinders where the signal will be used to set or reset the signal to the final control valves. 5. It is important to draw the motion diagram to understand the sequence of the actuation of various signal input switches, limit switches and sensors. 6. Motion diagram indicates the status of the cylinder position in a particular step; whether extended or retracted. Example 4: Two cylinders are used to transfer parts from a magazine onto a chute. When a push button is pressed, the first cylinder extends. Pushing the part from the magazine and positioning it in preparation for transfer by the second cylinder onto the outfeed chute. Once the part is transferred, the first cylinder retracts, followed by the second. Confirmation of all extended and retracted positions is required. Draw the pneumatic circuit using the classic method. 14 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Step 1: Write down sequences and draw motion diagrams Process Pushing from magazine (First cylinder) & transferring to outfeed chute (second cylinder) Number of cylinders 2 (because 2 processes) Cylinder A First cylinder Cylinder B Second cylinder Represent the process in notational form First cylinder extends: (A+) First cylinder retracts: (A-) Second cylinder extends: (B+) Second cylinder retracts: (B-) Sequence First cylinder extends, second cylinder extends, first cylinder retracts, second cylinder retracts A+ B+ A- BTherefore the sequence for this example is as follows: Figure 26: Displacement step diagram Step 1b: Draw motion diagram Figure 27: Displacement time diagram Step 1a: Identify the sequence Step 1c: Analyse the input and output signal Note: Cylinder A, the sensors could be labelled as a0 and a1 for easy identification. a0 a1 Cylinder A Input signals: Cylinder A – Limit switch at home position a0 Limit switch at home position a1 Cylinder B - Limit switch at home position b0 Limit switch at home position b1 Output Signal The forward motion of cylinder A ( A+) The return motion of cylinder A (A-) The forward motion of cylinder B( B+) The return motion of cylinder B( B-) 15 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Step 1d: Sequence flow – link input and output signal Figure 28: Input and output signal link a. A+ action generates sensor signal a1, which is used for B+ motion b. B+ action generates sensor signal b1, which is used for B- motion c. B- action generates sensor signal b0, which is used for A- motion d. A- action generates sensor signal a0, which is used for A+ motion The information above can be represented graphically as shown in figures 28a and 28b (sequence flow). Step 2a: Draw the power circuit a. Draw cylinders A and B as shown in Figure 29. b. Draw directional control valves 1.1 and 2.1 in unactuated conditions c. Mark the limit switch positions for cylinders A (a0 and a1) and B (b0 and b1) Figure 29: Power circuit Step 2b: Draw the control circuit Figure 30: Control circuit (in the red dotted box) Step 2: Draw in cylinders and control valves and complete the circuit intuitively 16 POLITEKNIK BANTING SELANGOR Figure 28b: Sequence flow a. Based on Figure 28b, connect all the limit switches accordingly, e.g. the Start pushbutton and limit switch b0 send signals to A+ and limit switch a1 sends signals to B+ to extend cylinder B.
PNEUMATIC CIRCUIT DESIGN Step 3: Analyse the circuit to ensure its functionality. Step 3a: Analysis of the pneumatic circuit Figure 31: Circuit for sequence A+ B+ A- B17 POLITEKNIK BANTING SELANGOR 1. Figure 31 shows the complete circuit for sequence A+ B+ A- B-. When the start button is pressed, the signal appears at port 14 (A+) of valve 1.1 through limit switch signal b0. 2. Always check if there is a signal present at the other end; i.e. port 12 (A-) of valve 1.1. Notice that the signal is not present at port 12 (A-) of valve 1.1. (Because b1 is not pressed by cylinder B). There is no signal conflict and valve 1.1 is able to move. So cylinder A advances to the forward position. 3. When cylinder A advances to the forward position, it generates a signal at limit switch signal a1, which is applied to port 14 (B+) of valve 2.1, thus cylinder B advances to the forward position. 4. Again check for the presence of the signal at the other end, port 12 (B-) of valve 2.1. The signal is not present at port 12 (B-) of valve 2.1 (because a0 is not pressed, A is already in an extended position now) hence there is no signal conflict. 5. The signal applied to port 14 (B+) of valve 2.1 causes the shifting of DCV 2.1 and cylinder B to extend. 6. Now, when cylinder B fully extends, it generates a limit switch signal b1, which is applied to port 12(A-) of valve 1.1. This causes cylinder A to retract and a0 is pressed. There is no signal conflict, as a0 and a1 are mutually exclusive signals. 7. When cylinder A is fully retracted, it generates a limit switch signal a0, which is applied to port 12 (B-) of valve 2.1 and cylinder B retracts.
PNEUMATIC CIRCUIT DESIGN The following images are screenshots of simulation software for sequence A+ B+ A- BInitial state Position when Cylinder A extends Position when Cylinder B extends Position when Cylinder A retracts Position when Cylinder B retracts Figure 32: Simulation for sequence A+ B+ A- BNote: red line indicates the line is pressurised (signal presents) and the blue line indicates the line is unpressurised (no signal) 18 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Example 5: In a workshop, a drilling operation is to be performed using a stamping machine. Before drilling, the workpiece has to be clamped under the stamping station. Then drilling tool bit comes and performs the drilling operation. The workpiece must be unclamped only after the drilling operation. Draw the pneumatic circuit using the classic method. Solution: The solution for this method must include all three steps as mentioned earlier. Let’s start. Step 1: Write down sequences and draw motion diagrams Process Drilling & Clamping Number of cylinders 2 (because 2 processes) Cylinder A Clamping Cylinder B Drilling Represent the process in notational form Clamp: cylinder A extends (A+) Unclamp: Cylinder A retracts (A-) Drill tool bit comes down: Cylinder B extend (B+) Drill tool bit goes up: Cylinder B retracts (B-) Sequence 1. Clamp workpiece (A+) 2. Drill tool bit comes down (B+) 3. Drill tool bit goes up (B-) 4. Unclamp (A-) A+ B+ B- ATherefore the sequence for this example is as follows: Step 1a: Identify the sequence Figure 33: Displacement step diagram Step 1b: Draw motion diagram Figure 34: Displacement time diagram 19 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Input signals: Cylinder A – Limit switch at home position ao Limit switch at home position a1 Cylinder B - Limit switch at home position bo Limit switch at home position b1 Output Signal The forward motion of cylinder A ( A+) The return motion of cylinder A (A-) The forward motion of cylinder B( B+) The return motion of cylinder B( B+) Step 1c: Analyse the input and output signal Step 1d: Sequence flow – link input and output signal Figure 35a: Input and output signal link a. A+ action generates sensor signal a1, which is used for B+ motion b. B+ action generates sensor signal b1, which is used for B- motion c. B- action generates sensor signal b0, which is used for A- motion d. A- action generates sensor signal a0, which is used for A+ motion The information above can be represented graphically as shown in figure 35a and 35b (sequence flow). Step 2a: Draw the power circuit a. Draw cylinders A and B as shown in Figure 36 b. Draw directional control valves 1.1 and 2.1 in unactuated conditions c. Mark the limit switch positions for cylinders A (a0 and a1) and B (b0 and b1) Figure 36: Power circuit Step 2: Draw in cylinders and control valves and complete the circuit intuitively Step 2b: Draw the control circuit Figure 37: Control circuit (in the red dotted box) 20 POLITEKNIK BANTING SELANGOR Figure 35b: Sequence flow
PNEUMATIC CIRCUIT DESIGN Step 3: Analyse the circuit to ensure its functionality. Step 3a: Analysis of the pneumatic circuit 1. Initially, limit switch a0 is actuated because it is pressed by Cylinder A. When the start button is pressed, the signal appears at port 14 of valve 1.1 through limit switch signal a0. 2. At the same time, there is a signal present at the other end (12) of valve 1.1. This results in signal conflict and valve 1.1 is unable to move as shown in figure 38. Figure 38: Signal conflict at valve 1.1 3. Now, let’s assume b0 is somehow disengaged for time being, so that valve 1.1 can actuate and consequently cylinder A can extend when the start button is pressed. 4. When cylinder A fully extends, it generates a signal at limit switch a1, which is applied to port 14 of valve 2.1 as shown in figure 39. 5. This time, no signal is present at the other end (12) of valve 2.1 hence there is no signal conflict. Figure 39: Pneumatic circuit after cylinders A and B are extended 6. Signal applied to port 14 of valve 2.1 causes the DCV 2.1 to switch over its position and causes cylinder B to extend. 7. When cylinder B fully extends, limit switch b1 is actuated and the output signal from limit switch b1 is applied to port 12 of valve 2.1. 8. However in figure 40, it can be seen that signal is also present at port 14 of valve 2.1 because a1 is also pressed by cylinder A. This results in signal conflict and valve 2.1 is unable to switch its control position. Figure 40: Signal conflict at valve 2.1 21 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN 9. Let us assume b1 is somehow disengaged for time being, so that valve 2.1 can switch over and consequently cylinder B can retract as in figure 41. 10. In figure 42, when cylinder B is fully retracted, limit switch b0 is actuated and the output signal of limit switch b0 is applied to port 12 of valve 1.1. 11. Since there is no signal present at port 14 of valve 1.1, thus there is no signal conflict and valve 1.1 can switch over causing Cylinder A to retract. Figure 41: Position when cylinder B is reversing (B -) Figure 42: Position when cylinder A has retracted fully (A-) Elimination of Signal Conflict 1. The interference between the control signals in multi cylinders circuit can be eliminated by using various methods such as: a. Idle return roller b. Reversing valves ( memory valves) c. Modules as a combination of valves 2. Cascading method uses the reversing valves (also known as group changing valves) and the step counter method uses modular valves. Both the idle return roller and cascade method are discussed in a subsequent section of this chapter. Use of Idle Return Rollers. 1. An idle-return roller limit switch is a directional control valve that is operated in one way. 2. If the continued signal has been generated from a limit switch, an idle return roller valve is used to eliminate the interference (signal conflict) between control signals. The two designs of the idle roller are shown in figure 43 Figure 43: Two designs of Idle return rollers (Image sources: SlideToDoc.com) 22 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN 3. Figure 44 shows how the idle return roller valve operates. The roller lever valve with idle return is actuated when the roller lever is traversed by the cam of a cylinder in a certain direction (Figure 44a). When the cylinder is fully extended, the valve is returned to its initial position by a return spring. (Figure 44 b) 4. When traversed in the reverse direction, the roller lever has an idle return and the valve is not actuated. (Figure 44 c and d) 5. As a result, the valve generates a short output pulse during the forward motion of the cylinder. The idle return mechanism also allows the cylinder to retract without re-activating the valve. 6. Hence, in the end position or during the return motion of the piston, the valve does not get actuated, and no output signal is produced. 7. For the generation of short output pulse by the idlereturn roller valve during the return motion of the cylinder, this valve may be positioned in the opposite direction as compared to the case during the forward motion of the cylinder. 8. Using the idle return roller valve is the most simple and economical solution to eliminate signal conflict. 9. With simple circuit design and wiring, and easy maintenance of the control system, the solution is much used for a simple sequence control with 2 or 3 cylinders. 10.The drawback of using idle return rollers valve is that a. It is difficult to precisely verify the position which means the end position cannot be sensed accurately. b. It is not reliable because unable to configure an AND logic circuit with other control signals because the limit switch only generates a short pulse signal. c. The length of the output pulse signal from the idle return roller valve varies depending on the speed of the cylinder. It is noted that the length of the pulse signal may not be enough for proper operation if the cylinder moves too fast. (fast control system cannot be set up) Figure 44: Actions of idle return rollers (Image sources: SlideToDoc.com) 11. In the previous sequence problem, we have identified that roller valves b1 and a1 are responsible for signal conflicts. To eliminate the problem of signal conflicts the roller valves b1 and a1 are to be replaced by idle return rollers as shown in figure 45. 23 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Figure 45: Solution using idle return roller valve for sequence A+ B+ B- A- (Example 5) Cascade method 1. Signal elimination by means of a reversing valve or bi-stable memory valve is often used. Steps to develop cascade circuit 1. Identify the sequence from the given task. 2. Draw the motion diagram 3. Find the following information from the sequence: ❑ Number of groups = N; (Note: the same cylinder cannot be in the same group) ❑ Number of pressure lines = N; (Note: same as the number of groups) ❑ Number of reversing valves = N – 1; (Note: Number of groups – 1) 2. A cascade control circuit uses non-directional limit switches and memory type 4/2-way valves or 5/2-way valves, which are generally used to control the double-acting cylinders, to control the traffic of control signals. Figure 45 shows the solution for sequence A+ B+ B- A- using the idle–return rollers valves. The valves are placed at limit switch b0 and a1 because these are the limit switches that cause signal conflicts. 4. Draw the power circuit 6. Analyse the circuit. 5. Draw the pressure lines, group changing circuit and control valves above and below the pressure lines 24 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Note: For 2 groups, 2 Pressure lines and 1 Reversing memory valves Note: For 3 groups, 3 Pressure lines and 2 Reversing memory valves Signal 3 Example 6a: Draw the sequence flow for A+ B+ A- BFind the following information from the sequence: ❑ Number of groups = N; (Note: the same cylinder cannot be in the same group) ❑ Number of pressure lines = N; (Note: same as the number of groups) ❑ Number of reversing valves = N – 1; (Note: Number of groups – 1) Control circuit below the pressure lines Figure 46: Sequence flow for A+ B+ A- BFigure 47: Group changing connection 25 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Example 6b: Draw the pneumatic circuit for A+ B+ A- B- using the cascade method based on sequence flow in Example 6a Solution: 4. Draw the power circuit 5. Draw the pressure lines, group changing circuit and control valves above and below the pressure lines as shown in Figure 49. Figure 48: Power circuit Figure 49: Cascade circuit for sequence A+ B+ A- B26 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN 6. Analyse the circuit. 1. Initially, limit switches a0 and b0 are actuated because cylinders are pressing them. When the start push button is pressed, the signal is present at signal 1 of the group changing valve and it is actuated since there is no signal present at signal 2. 2. This causes all the components (A+, a1 and b1) connected to the pressure line L1 to be powered up. At this point, cylinder A extends first and actuates a1 (note: a0 is de-actuated). This actuation makes cylinder B extends. 3. When cylinder B touches limit switch b1, a signal is present at Signal 2 of the group changing valve. Now, the group changing valve switches its position to the right control box and pressure line L2 is powered up. The components connected to L2 are now getting the pressure source and cylinder A retracts and actuates limit switch a0. This actuation causes cylinder B to retract and actuates b0 (Note: b1 is de-actuated, no signal at Signal 2) Figure 50: Cascade circuit for sequence A+ B+ A- B27 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Example 6 Cylinder A extends to clamp the workpiece before cylinder B extends to perform the stamping job. Cylinder A can return back only after cylinder B has retracted fully. Design the pneumatic circuit using the cascade method. Solution: Figure 51: Solution for sequence A+ B+ B- A28 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Example 7 Design pneumatic circuit for A+ C+ C- B+ A- B- using cascade method. Show steps to develop the circuit. Include sequence flow and step diagram in the solution. Solution: Figure 52: Solution for Example 7 Motion diagram 29 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN PNEUMATIC CIRCUIT DESIGN TUTORIAL 1. The allocating device supplies aluminium valve blanks to a machining station. The piston rod of the single-acting cylinder (1.0) is made to advance by operating a push button. After releasing the actuating button, the piston rod returns. Draw the pneumatic circuit using direct and indirect methods. Figure 53: Allocating device 2. Figure 2 shows a sorting device for metal stampings. When the push button on the actuating valve is pressed, metal stampings lying in random positions are sorted out and transferred to a second conveyor belt. The forward motion of the piston rod of a single-acting cylinder (1.0) takes t = 0.4 seconds. When the push button is released, the piston rod travels to the retracted end position. A pressure gauge is fitted before and after the oneway flow control valve. Draw the pneumatic circuit using direct and indirect methods. Figure 54: Sorting device for metal stampings 3. With the help of the vertical switching point, soft cool (lignite) briquettes are to be fed to an upper or lower conveyor, according to selection. The destination of the swivelling slide (upper or lower) is decided by means of a valve with a selector switch. The upward motion of the double-acting cylinder (1.0) is to take place in t1 = 3 seconds; the downward motion in t2 = 2.5 seconds. Pressure on both sides of the piston is indicated. In the initial position, the cylinder assumes the retracted end position. [Lignite briquettes are the classic fuel for traditional solid-fuel appliances like automatic stoves, cooking stoves and stand-alone stoves. Frequently used in combination with wood in modern solid-fuel appliances.] Draw the pneumatic circuit using direct and indirect methods. Single cylinder circuit design 30 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Figure 55: Vertical switching point for briquettes 4. Operation of two identical valves by push button causes the forming tool of an edge folding device to thrust downwards and fold over the edge of a flat sheet of cross-sectional area 40 x 5. If both – or even just one – push button is released, the double-acting cylinder (1.0) slowly returns to the initial position. The cylinder pressures are indicated. Draw the pneumatic circuit using the indirect method. Figure 56: Edge folding device 5. Surveyor’s measuring rods in 3 or 5 m length are marked in red with 200 mm graduations. There is a choice of two push buttons to start the forward movement of the measuring rods via cylinder (1.0), which has the exhaust air throttled. The return stroke, also started by a push button, can only take place when the double-acting cylinder (1.0) has reached its forward end position. Draw the pneumatic circuit using the indirect method. Figure 57: Marking machine 6. A plastic component is to be embossed by using a die which is powered by a double-acting cylinder. When a pushbutton, S1 is pressed, the cylinder extends to perform the embossing process. The return of the die is to occur only when the cylinder rod has fully extended to the embossing position and the preset pressure is reached. A roller lever valve, S2 is to be used to confirm the full extension. The signal for retracting must only be generated when the piston rod has reached the embossing position. The pressure in the piston chamber is indicated by a pressure gauge. Construct the pneumatic circuit using the indirect method. The circuit should be labelled clearly. 31 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN 7. A double-acting cylinder guides cylinder pins towards a measuring device. The pins are separated by means of a continuous to-and-fro movement. The oscillating motion (use limit switch a0 and start pushbutton, S1 to extend meanwhile limit switch, a1 to retract) can be started by means of a valve with selector switch, S1. The duration of the forward stroke of the cylinder is to be t1= 0.6 s, and the return stroke t3 = 0.4 s. The cylinder is to remain in the forward end position for t2 = 1.0 s, resulting in a cycle time of t4 = 2.0 s. Construct the pneumatic circuit. 8. An electrically heated rail is pressed onto a rotatable cold drum by a double-acting cylinder and welds a continuous plastic sheet into pieces of tubing. The forward stroke is triggered by means of a push button. The maximum cylinder force is set at 4 bar via a pressure regulator with a pressure gauge. (This prevents the welding rail from damaging the metal drum). The return stroke is not initiated until the forward end position has been acknowledged and the pressure in the piston area has reached 3 bar. The supply air is restricted for the movement of the cylinder. The flow control should be adjusted so that the pressure increase to 3 bar only takes place after t1 = 3 seconds after the cylinder has reached the forward end position (the foil edges which are overlapped are welded by the heated welding rail as increased pressure is applied). Restarting is only possible when the retracted end position has been reached and a time of t2 = 2 seconds has elapsed. Reversing a 3/2-way valve with a selector switch causes the control to be switched to a continuous cycle. 9. Bulk loose material is to be emptied from a dump hopper by means of a double-acting cylinder. By pressing a push button S1, the dump hopper is tilted and the bulk loose materials are emptied out. By pressing another push button, S2, the dump hopper is returned to its initial position. Construct the pneumatic circuit using the indirect method. 10.Sheet metals are to be U-formed using a bending machine which uses a double-acting cylinder as shown in Figure 1. By pressing a push button S1, the cylinder thrust forward to bend the sheet metal. By pressing another push button, S2, the cylinder is returned to its initial position. Construct the pneumatic circuit using the indirect method. 11.Sheet metals are to be U-formed using a bending machine which uses a double-acting cylinder. By pressing a push button S1, the cylinder thrust forward to bend the sheet metal. The cylinder is returned to its initial position after it reaches the end position which is confirmed by a roller limit switch. Construct the pneumatic circuit using the indirect method. 12.Parts are accumulating on a conveyor belt and waiting to be released and transferred to the next phase of assembly. Technicians at three (3) stations need to control the gate release mechanism to have parts sent to their assembly station. You are required to design the pneumatic circuit where there are three pushbuttons (each at a station). When any of the push buttons is pressed, the single-acting cylinder is advanced to open the gate and release the part to the assembly station. The cylinder retracts when all the push buttons are released. 13. The allocating device supplies aluminium valve blanks to a machining station. By operating any two identical push buttons, the piston rod of the double-acting cylinder (1.0) is made to advance. The piston rod is made to retract by pressing another pushbutton and the cylinder only retracts once it has reached the forward end position. Design the pneumatic circuit. 32 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Multi cylinders circuit design 1. Two clips are to be riveted together on a semiautomatic press. Components and rivets are positioned by hand and then removed by hand on completion of the riveting operation. The automated part of the working cycle consists of the holding and clamping of the components by cylinder A and also the riveting by cylinder B. The clamp must be activated before the riveting cycle begins and deactivated at the end of the riveting cycle. The operation is started by pressing a pushbutton, Start. Design a pneumatic circuit for the given problem using the classic method. 2. In a production line, parts need to be clamped for drilling operations. The technician needs to activate and deactivate the pneumatic clamp that holds the part in a fixture on the drilling machine. The clamp must be activated before the drilling cycle begins and deactivated at the end of the drilling cycle. The operation is started by pressing a pushbutton, Start. Design a pneumatic circuit for the given problem using the classic method. 3. In a production line, parts need to be clamped for stamping operation. The technician needs to activate and deactivate the pneumatic clamp that holds the part in a fixture on the stamping machine. The clamp must be activated before the stamping cycle begins and deactivated at the end of the stamping cycle. The operation is started by pressing a pushbutton, Start. Design a pneumatic circuit for the given problem using the classic method. 4. Two cylinders are used to transfer parts from a magazine onto a chute. When a push button is pressed, the first cylinder extends, pushing the part from the magazine and positioning it in preparation for transfer by the second cylinder onto the outfeed chute. Once the part is transferred, the first cylinder retracts, followed by the second cylinder. Design a pneumatic circuit for the given problem using the classic method. 5. Two cylinders are used to transfer parts from a magazine onto a chute. When a push button is pressed, the first cylinder extends, pushing the part from the magazine and positioning it in a chute. Then the cylinder retracts. Next, the second cylinder pushes the part from the chute to a box. Once the part is transferred to the box, the second cylinder retracts. Design a pneumatic circuit for the given problem using the classic method. 6. In a press shop, stamping operation is to be performed using a stamping machine. Before stamping, the workpiece has to be clamped under the stamping station. Then stamping tool comes and performs the stamping operation. The workpiece must be unclamped only after the stamping operation. a. Design a pneumatic circuit for the given problem using the classic method. Your solution must include the following i. Sequence flow diagram. ii. Displacement-step diagram. b. For the above questions, is there any signal conflict? If yes, at which point does it occur, analyse the occurrence of the signal conflict clearly. c. Redesign the above circuit using the cascade method. The solution must be shown clearly. 33 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN PNEUMATIC CIRCUIT DESIGN EXERCISE Answers 34 POLITEKNIK BANTING SELANGOR Exercise 3 Exercise 4 a. 3/2-way NC single pilot, spring return DCV b. 5/2-way double pilot DCV c. 3/2-way NC double pilot DCV d. 5/2-way single pilot, spring return DCV Exercise 5 a. Meter-in method controls retract b. Meter-out method controls retract Exercise 2 Exercise 1
PNEUMATIC CIRCUIT DESIGN PNEUMATIC CIRCUIT DESIGN TUTORIAL Answers Single cylinder circuit design - Answers Question 1 Question 2 Indirect method 0 bar 0 bar Question 3 Question 4 35 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Question 5 Question 6 Question 7 Question 9 Question 10 & 11 Question 12 36 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Question 8 Multi cylinders circuit design - Answers Question 1, 2 and 3 Sequence flow Displacement step diagram Classic circuit However, this circuit creates signal conflicts at roller limit switches b0 and a1. To eliminate the signal conflict, use the idle return roller limit switch or cascade method as shown below. 37 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Classic circuit using idle return roller valve Cascade method 38 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Question 4 Sequence flow Displacement step diagram Classic circuit Cascade method 39 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Sequence flow Classic circuit Displacement step diagram Question 5 Question 6 Question 6a (i) Question 6a (ii) Question 6a (iii) There is a signal conflict occurring in the circuit. The first signal conflict occurs he DCV 1.1 at pilot 12. The presence of the signal is due to the limit switch b0, which is pressed by Cylinder B. The second signal conflict occurs at DCV 2.1 at pilot 14. This is because the signal present at limit switch a1 is pressed by Cylinder A which is in the extended position. Question 6b 40 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN Question 6c 41 POLITEKNIK BANTING SELANGOR
PNEUMATIC CIRCUIT DESIGN References 42 POLITEKNIK BANTING SELANGOR 1. SMC Pneumatics Inc. (1997). Basic pneumatics (Rev. 0100 ed.) [E-book]. 2. FESTECH Factory Automation Expert Group. (2007). Practical pneumatics FESTECH. 3. Jainik Makwana (2019). Oil Hydraulics and Pneumatic Chapter 7 Pneumatic Circuit. Department of Mechanical Engineering Darshan Institute of Engineering & Technology, Rajkot 4. P. Croser, F. Ebel (2002). Pneumatics Basic Level (Edition 10). Festo Didactic GmBH & Co. 5. D. Waller, H Werner (2002). Pneumatics Workbook Basic level (Edition 04). Festo Didactic GmBH & Co. “Education is one thing no one can take away from you.” —Elin Nordegren