Types of Directional Control Valves

Report
Actuators and directional
control valves
1.
2.
3.
4.
5.
6.
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.
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
7.

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) Fig. 3.3: 3/2 way DCV push
button (N/C) after actuation
to port (2).

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
(a) 3/2 way directional
air flows through the valve.
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
Picture of 3/2 way DCV
shows the picture of the valve.

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) (a) Initial position (before actuation)
while the exhaust will be from port (4)
to port (5)
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
ISO symbol of
5/2 way valve
port (2) to port (3)
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
FOOT PEDAL
2. Mechanical actuators
ROLLER
3. Electrical actuators
SOLENOID
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 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.
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 It uses compressed air in
the forward stroke while both forward and
the return stroke is
backward strokes
achieved by the spring.
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
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 class

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