Warm Up Activity on Module 7

Team A vs. Team B

Lets play Jeopardy !!

1. What does a time delay used for in a pneumatic circuit?

2. List the 3 combined valves used to form Pneumatic time

elements.

3. What is the function of a time delay valve?

4. Draw the ISO symbol for the time delay valve in both normally open

and normally close.

5. In steps, explain the principal of operation of the time delay.

6. The type of the time delay valve whether normally opened or normally

closed is determined according to the type of the 3/2 way valve if it is N/O

or N/C. > True or False.

Demonstrate an understanding of the pneumatic time element. Demonstrate an understanding of the different types of time delay valves. Identify the symbol, and design of normally closed time delay valve. Explain the function and principle of operation of normally closed time delay valve. Identify the main parts of the time delay valve. Draw a pneumatic circuit diagram that consists of a time delay valve, normally closed. Simulate pneumatic circuit that consists of a time delay valve using Fluid SIM software. Build a pneumatic circuit that consists of a time delay valve as per specific requirements. Explain the the main types of displacement diagrams. Draw a displacement step diagram for a given sequence of operation. Draw a circuit diagram from a given sequence of operation.

Pneumatic time elements can be

formed very simply from

combinations of three valves:

1. Directional control valve,

2. One way flow control valve

and,

3. Reservoirs.

Time delay valve is used to delay the output

signal.

The time delay valve is actuated by a

pneumatic signal through the tank after a

preset time delay has elapsed.

The returned to the normal position via return

spring when the signal is terminated.

Fig. (7.1) shows the picture of the time delay

valve, normally closed.

(a) ISO symbol of N/C time

delay valve (fluidSIM)

(b) ISO symbol of N/O time

delay valve(fluidSIM)

The time delay valve is a combination of a 3/2 way valve, one

way flow control valve and air reservoir.

The 3/2 way valve can be normally open or normally closed.

The delay time is generally ranging between (0-300) seconds

for both types of valves (normally opened and normally

closed).

By using additional reservoirs, the delaying time can be

extended.

The type of the time delay valve whether normally opened

or normally closed is determined according to the type of the

3/2 way valve if it is N/O or N/C.

Fig. 7.3: parts of the time delay

valve

Fig. 7.4.a 3/2 way valve (N/C)

Fig. 7.4.a 3/2 way valve (N/O)

The following operational principle applies for a time

delay valve in normally closed position

The control air flows into the valve at 12 through a

one way flow control valve and depending on the

setting of the throttling screw, a greater or lesser

amount of air flows per unit of time into the air

reservoir, when the necessary control pressure has

built up in the air reservoir, the pilot control of the

3/2 way valve is moved downwards. This blocks the

passage from 2 to 3.

The valve disc is lifted from its seat and thus air can

flow from1 to 2 as shown in Fig. (7.5.b).

The time required for pressure to build up in the air

reservoir is equal to the control time of the valve.

(a) Un-actuated position

(b) Actuated position

Learning objectives:

• Familiar with the set-up and mode of operation of a time delay valve normally closed.

• Able to recognize and sketch the time delay valve.

• Able to choose different pneumatic components according to the given conditions.

Problem Description:

A double acting cylinder is used to press glued components together.

Upon operation of a push button, the clamping cylinder extends as shown in Fig. 7.6 below.

Once the fully advanced position is reached, the cylinder is to remain for a time of T = 6 seconds

and then retract to the initial position automatically.

The cylinder retraction is to be adjustable.

A new start cycle is only possible after the cylinder has

fully retracted.

The limit switch 1S2 must be actuated as a start condition.

And by pressing the push button switch 1 S1, two signals will reach the two pressure

valve 1 V1, which in turn will pass the pressure signal to port 14 of the 5/2 way valve

1V3.

The valve 1V3 reverses resulting in advancing the piston rod of the cylinder 1A with

a specific speed according to the setting of the one way flow control valve1 V4.

When the cylinder reaches the forward end position, it will activate the limit

switch 1S3.

The air reservoir of the time delay valve starts filling up, and after the adjusted time

elapsed, the valve 1V2 will pass the Pressure signal to port 12 of the valve 1V3.

The valve 1V3 reverses, and the piston rod retracts to the initial position with

adjusted speed determined by the one way flow control valve 1V5.

A control system with compulsory stepped

operation where switching from one step to the

next in the program is dependent upon certain

conditions being satisfied.

In particular, the programming of jumps, loops,

branching, etc. is possible.

A video

(1) Time-dependent sequence control system

A sequence control where the switching conditions are

dependent only on time.

Step enabling conditions are generated via timers, or cam-shaft

controllers with constant speed.

(2) Process dependent A sequence control system where the switching conditions are

dependent only on signals from the system being controlled.

Step diagram control is a form of process-dependent

sequence control; the step enabling conditions depend purely

on the stroke-dependent signals of the controlled system.

In the case of multiple cylinder circuits, a clear definition

of the problem is important.

The representation of the desired motion of all actuators is

described using the displacement-step diagram.

The special conditions for the start of the sequence

must also be defined.

If the motion diagram and auxiliary conditions have been

clearly defined, drawing of the circuit diagram can

commence.

The circuit diagram should be designed according to the

guidelines, in order for a circuit to operate, it is

essential to avoid overlapping signals.

By an overlapping signal, we understand signals

applied simultaneously at the two control ports of a

double pilot valve.

The following valves can be used to eliminate signal

overlap: roller lever valves with idle return or toggle

lever valves, time delay valves, reversing valves or

sequencers.

The displacement step diagram and the displacement time

diagram represents the operating sequence of the actuators,

the displacement is recorded in relation to the sequence

step.

If a control system incorporates a number of actuators, they

are shown in the same way and are drawn one below the

other.

Their interrelation can be seen by comparing the steps as

Shown in (Fig.7.7b).

There are two cylinders 1A and 2A.

In step 1 cylinder 1A extends and then cylinder 2A

extends in step 2.

In step 3 cylinder 1A retracts and in step 4 cylinder 2A

retracts.

Step number 5 is equivalent to step 1.

(a) Positional sketch

(b) Displacement step diagram

In the case of a displacement-time diagram, the

displacement is plotted in relation to the time

as shown in (Fig.7.7c)

(c) Displacement time diagram

Find the sequence of operation for the given

displacement step diagram

Solution:

A+A-B+B-C+C

Draw the displacement step diagram for the

following sequence of operation A+B+B-A-C+C

Solution:

For further reading, you can use the following links:

1- www.Fest-didactic.com

2- http://www.eng2all.com/vb/t28732.html

3- http://www.logiclab.hu/lesson.php?fe=2

10. Supplementary recourses

1. Pneumatics video from Festo.

2. FluidSIM software.

11. References

1- Festo manuals and workbook TP101

2- Festo manuals and textbook TP101

1. Draw the symbol of time delay valve,

normally closed

2. Draw the symbol of 3/2 way, roller lever

valve

3. Draw the symbol of 5/2 way, double pilot

valve

4. What is the function of time delay valve?

5. What are the three parts consisting the time

delay valve?

A rod of a double acting cylinder is

advanced by pressing a push button valve,

after reaching the end position; it stays 5

seconds and then returns automatically to

the initial position. Draw the required circuit

diagram.

Submission of homework 6 is

in week 9.

Homework 6 posted on

weebly

Your practical quiz will be in week 9 –

more details have been announced

during last class in week 7.