Transcript Types of Directional Control Valves
Actuators and directional control valves
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Differentiate between the main types of directional control valves.
Demonstrate the function and uses of 3/2 way valve, push button actuated.
Demonstrate the function and uses of 3/2 way valve, roller lever actuated.
Explain the function and uses of 5/2 way valve, selector valve. Explain the function and uses of 5/2 way valve, pilot valves.
Explain the main types of pneumatic actuators.
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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 circuit using DCV, single and double acting cylinders on the Festo trainer and check their operation
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
3/2 WAY
A) 3/2 way DCV Push Button N/C B) 3/2 way DCV Push Button N/O C) 3/2 way DCV Roller Lever N/C D) 3/2 way DCV Selector
3/2 WAY
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.
(b) 3/2 way DCV push button (NC) (before actuation) 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). Fig. 3.3: 3/2 way DCV push
button (N/C) after actuation
3/2 WAY
A) 3/2 way DCV-push button - Normally Closed (N/C) 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
3/2 WAY
A) 3/2 way DCV-push button - Normally Closed (N/C) Actuated
Allows the flow from port (1) to port (2) and blocking the exhaust port (3) .
ISO symbol of 3/2 way valve normally closed (N/C) and spring reset. Picture of the valve.
3/2 WAY
B) 3/2-DCV - push button - Normally Open (N/O) Way of operation:
Normally open means that compressed air flows through the valve.
(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).
3/2 WAY
B) 3/2-DCV - push button - Normally Open (N/O) 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).
ISO symbol of 3/2 way DCV push button (NO)
Actuated
Allows the flow from port (2) to port (3) and blocking the supply air port (1).
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).
3/2 WAY
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
3/2 WAY
C) 3/2 Way-DCV- Roller Lever Valve - Normally closed (N/C) 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.
3/2 WAY
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 .
5/2 WAY
**** 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).
1) 5/2 way Selector Valve 2) 5/2 way Single Pilot 3) 5/2 way Double Pilot
5/2 WAY
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) (a) Initial position (before actuation)
After actuation
After operating the valve by any method, the valve will be shifted to the other (b) Second position (after actuation) 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) ISO symbol of 5/2 way valve
5/2 WAY
1) 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. The valve keeps the last position active as the 3/2 way selector.
5/2 WAY
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.
5/2 WAY
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.
The pneumatic directional control valves can be actuated (operated) in several ways such as follows: 1. Manual Actuators 2. Mechanical Actuators 3. Electrical Actuators
1. Manual actuators MANUAL PUSH BUTTON 2. Mechanical actuators ROLLER 3. Electrical actuators SOLENOID FOOT PEDAL IDLE RETURN ROLLER 4.Electrical actuators PNEUMATIC – PRESSURE
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 single acting 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.
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 .
A direct control circuit of a double acting cylinder is shown in Fig. 3.15 to the left.
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 2 It has one port It has a spring. It has 2 ports 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.
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