Actuators and directional control valves - Miss Hanna's...
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Transcript of Actuators and directional control valves - Miss Hanna's...
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)
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.
(a) pressure
port (1) is
blocked
(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).
When the push button is actuated the valve is closed, thus
stopping the air to flow from port (1) to port (2).
(a) 3/2 way directional
control valve 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).
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.
ISO symbol of 3/2 way
DCV push button (NO)
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
Construction Picture of the roller lever
valve
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/robotic-
control/precision-motion-using-pneumatic-actuators
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 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 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
There are two ways to control
pneumatic cylinders:
1- Direct control
2- Indirect control
How to control pneumatic
cylinders?
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.
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:
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.
After the slide has reached the forward end position it
returns to its start position.
Fig. 3.16: Positional sketch
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 • 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.
Fig. 3.17: Positional sketch
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