Actuators and directional control valves

Actuators and directional control valves

1. Differentiate between the main types of directional control valves. 2. Demonstrate the function and uses of 3/2 way valve, push button actuated. 3. Demonstrate the function and uses of 3/2 way valve, roller lever actuated. 4. Explain the function and uses of 5/2 way valve, selector valve. 5. Explain the function and uses of 5/2 way valve, pilot valves. 6. Explain the main types of pneumatic actuators.

7. Explain the function of the single acting cylinder and the double acting cylinder. 8. Describe the main types of controlling single acting cylinder and double acting cylinders 9. Draw the required circuit diagram as per the given specifications. 10. Use the FluidSIM software to build and simulate a pneumatic circuits that contain DCV, single and double acting cylinders. 11. Safely use the pneumatic Festo trainers to build different circuits. 12. Build a pnueumatic circuits using DCV, single and double acting cylinders on the Festo trainer and check their operation

A DCV video for you

Directional control valves are devices which influence the path taken by an air stream. The directional control valve is represented by two numbers. The first number represents the number of ports, and the second number represents the number of positions DCV Ports and positions

a) 3/2 way DCV-push button - Normally Closed (N/C) (a) pressure port (1) is blocked Function: The DCV allows the air flow into different paths from one or more sources. Way of operation: A 3/2-way valve has 3 ports and 2 switching positions. Normally closed means that compressed air cannot flow initially through the valve. When the pushbutton is actuated the valve is opened, thus allowing the air to flow from port (1) to port (2) as shown in Fig. 3.3. (b) 3/2 way DCV push button (NC) (before actuation) Fig. 3.3: 3/2 way DCV push button (N/C) after actuation

Un-actuated In normally closed 3/2 way valve, a spring-loaded 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 Fig on the right. (b) 3/2 way DCV push button (NC) (before actuation

Actuated Allows the flow from port (1) to port (2) and blocking the exhaust port (3) as shown in Fig. (3.3). ISO symbol of 3/2 way valve normally closed (N/C) and spring reset. Picture of the valve.

b) 3/2-DCV - push button - Normally Open (N/O) Way of operation: Normally open means that compressed air flows through the valve as shown in Fig. (3.5.a). (a) 3/2 way directional control valve N/O When the push button is actuated the valve is closed, thus stopping the air to flow from port (1) to port (2).

Un-actuated In the normally open 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 Allows the flow from port (2) to port (3) and blocking the supply air port (1). ISO symbol of 3/2 way DCV push button (NO) Fig. (3.5.b) to the left shows the ISO symbol of 3/2 way valve Normally open (N/O) and spring reset, and Fig. 5.5.c shows the picture of the valve. Picture of 3/2 way DCV push button (N/O).

c) 3/2 Way-DCV- Roller Lever Valve - Normally closed (N/C) One of the most important types of valve actuation. It is generally known as pneumatic limit switch. Symbol and Construction ISO symbol Picture of the roller lever valve Construction

Way of operation: This valve is actuated by pressing the roller lever e.g. by means of cylinder trip cam. The valve is returned to the normal position via return spring after releasing the roller lever.

d) 3/2 way, DCV selector valve The way of operation of the selector valve is the same as the 3/2 DCV push button. The only difference that the selector valve is keeping the last position active either it is NO or NC. Fig. 3.7 shows the picture and the ISO symbol of the 3/2 way, selector valve.

e) 5/2 way Directional Control Valve This valve contains 5 ports and 2 positions. The 5/2 DCV could be actuated manually or by using pressure actuation (single pilot and double pilot), or by electrical actuation (solenoid).

Before actuation When the 5/2-way valve is not actuated, the flow will be from port (1) to port (2) while the exhaust will be from port (4) to port (5) as illustrated in Fig. 3.8.a After actuation After operating the valve by any method, the valve will be shifted to the other position and in this case, the flow will be from port (1) to port (4) while the exhaust will be from port (2) to port (3) as shown in Fig. (3.8.b). (a) Initial position (before actuation) (b) Second position (after actuation) ISO symbol of 5/2 way valve

a) 5/2 way selector valve This valve is used for manual operation. You can control the valve by selector switch. It is used in simple applications. Fig. 3.9 above shows the picture and the ISO symbol of the valve. The valve keeps the last position active as the 3/2 way selector.

b) 5/2 way single pilot valve This valve is used for automatic operation You can control the valve by a pneumatic signal and a spring return. Fig. 3.10 above shows the picture and the ISO symbol of the valve.

c) 5/2 way double pilot valve This valve is used for automatic operation You can control the valve by two pneumatic signals The valve keeps the last position after removing the applied signal, and it is sometimes called memory valve. Fig.3.11 above shows the picture and the ISO symbol of the valve.

The pneumatic directional control valves can be actuated (operated) in several ways such as follows: 1. Manual Actuators 2. Mechanical Actuators 3. Electrical Actuators

A video for you Linear Actuators

1. Manual actuators Fig. (3.12.a) shows (from left to right) three manual actuation methods: manual, push button and foot pedal. 2. Mechanical actuators Fig. (3.12.b) shows (from left to right) two mechanical actuation methods: roller and idle return roller. 3. Electrical actuators Fig. (3.12.c) shows an example of electrical actuation (solenoid valve). See figure on page 8 in module 3 See figure on page 8 in module 3

A video on Pneumatics Actuators in industry http://www.packworld.com/controls/roboticcontrol/precision-motion-using-pneumaticactuators Video 2

They are used to produce the required forces in the pneumatic systems. The pneumatic actuators are divided into: Linear actuators Single acting cylinder Double acting cylinder Rotary actuators Air motors

Single acting cylinder is an output device. Its function: To convert the pressure energy to mechanical energy (linear force in one direction only).

The piston rod of a singleacting cylinder is to advance when a push button is operated. When the push button is released, the piston is to automatically return to the initial position. A 3/2-way valve controls the single-acting cylinder. The valve switches from the initial position into the flow position, when the push-button actuator is pressed.

Double acting cylinder is an output device. Its function to convert the pressure energy to mechanical energy (linear force and motion in two directions).. Note: The force produced by the piston during the advance stroke is greater than the force produced during the return stroke due to the area difference between the two sides of the piston.

A direct control circuit of a double acting cylinder is shown in Fig. 3.15 to the left. The piston rod of a double-acting cylinder is to advance when a 5/2 selector valve is operated and to return to the initial position when the selector switch is back to the normal position. The double-acting cylinder can carry out work in both directions of motion, due to the full air supply pressure being available for extension and retraction.

1. Opening and closing doors, 2. Taking items off conveyor belts and putting items on conveyor belts. 3. Lifting and moving packages around. 4. Presses and punches.

Comparison between single and double acting cylinder SERIAL SINGLE ACTING CYLINDER DOUBLE ACTING CYLINDER 1 It has one port It has 2 ports 2 It has a spring. It has no spring 3 It exerts force in one direction only. It exerts force in 2 directions (forward and backward) 4 It uses compressed air in the forward stroke while the return stroke is achieved by the spring. It uses compressed air in both forward and backward strokes

How to control pneumatic cylinders? There are two ways to control pneumatic cylinders: 1- Direct control 2- Indirect control

The simplest level of control for the single or double acting cylinder involves direct control signals. The cylinder is actuated directly via a manually or mechanically actuated valve, without any intermediate a switching of additional directional control valves. If the port sizes and the flow values of the valve are too large, the operating forces required may be too great for direct manual operation. Reference values for limits of direct cylinder control: Cylinder with piston diameter smaller than 40 mm Valves with connection sizes smaller than 1/4"

Cylinders with a large piston diameter have a high air requirement. A control element with high nominal flow rate must be used to actuate these. If the force should prove too high for a manual actuation of the valve, then an indirect actuation should be constructed, whereby a signal is generated via a second smaller valve, which will provide the force necessary to switch the control element.

The following safety precautions should be strictly followed in the pneumatics lab. 1. Wear the safety gear before starting any practical work on the trainer. 2. The working pressure shouldn t exceed 6 bar, that could be achieved by adjusting the pressure regulator in the air service unit to 6 bar. 3. Securely plug in pneumatic devices. 4. Keep piston rod travel free. 5. Check all connections before connecting the compressed air. 6. Do not exceed the maximum pressure. 7. Do not completely unscrew the regulating screw. 8. Tighten each locknut after setting the regulating screw. 9. Never tighten the regulating screw with force. 10. Never operate roller by hands. 11. Connect the compressed air supply only when you complete all connections.

After the slide has reached the forward end position it returns to its start position. 7.1 Learning objectives: Upon the completion of this task, the student will be familiar with indirect actuation of a double acting cylinder by using a double pilot valve. Using the 3/2 way roller valve for automatic return of the cylinder. 7.2 Task description: Fig. 3.16: Positional sketch Wooden planks are to be pushed along from a gravity feed magazine to a clamping device as shown in Fig.3.16. By pressing a pushbutton valve one plank is pushed by the slide out of the gravity feed magazine.

7.3 Task requirements: 1. Draw pneumatic circuit diagram to control the movement of the slide. 2. Simulate the circuit using Fluid SIM software. 3. Assemble the circuit practically and check its operation. Draw the Pneumatic Circuit in the table provided in your module

8.1 Learning objectives: Upon the completion of this task, the student will be Fig. 3.17: Positional sketch Familiar with indirect actuation of a double acting cylinder by using a double pilot valve. Familiar with using different types of directional control valves. 8.2 Task description: Using a diverting device, parts are to be moved from one conveyor track onto the other in a linear sequence as illustrated in Fig. 3.17. By operating a selector valve the oscillating piston rod of a cylinder pushes the turntable via a pawl in stepped sequence. The parts are diverted and transported onwards in the opposite direction. By returning the selector valve back to the normal position The drive unit is switched off.

8.3 Task requirements: 1. Draw a pneumatic circuit diagram to control the operation of the piston. 2. Simulate the circuit using FluidSIM software. 3. Assemble the circuit practically and check its operation. Draw the Pneumatic Circuit in the table provided in your module

9.1 Learning objectives: Upon the completion of this task, the students will be Familiar with indirect actuation of a single acting cylinder. Able to compare between direct and indirect control. 9.2 Task description: A single-acting cylinder with a large piston diameter is to clamp a workpiece following actuation of a push button. The cylinder is to retract once the push button is released. Positional sketch

9.3 Task requirements: 1. Draw a pneumatic circuit diagram to control the operation of the piston. 2. Simulate the circuit using FluidSIM software. 3. Assemble the circuit practically and check its operation. Draw the Pneumatic Circuit in the table provided in your module

10. For further reading, you can use the following links: 1- www.fest-didactic.com 2- http://www.eng2all.com/vb/t28932.html 3- http://www.logiclab.hu/lesson.php?fe=2 11. Supplementary recourses 1. Pneumatics video from Festo. 2. FluidSIM software. 12. References 1- Festo manuals and workbook TP101 2- Festo manuals and textbook TP101

Do the worksheet at the end of module 3 in class

Don t forget to submit homework 3 next week/class after the long weekend