Actuating a shut-off device

Learning objectives After completing this exercise:

 You’ll be familiar with one type of signal storage in pneumatic control systems.

 You’ll be able to adjust cylinder advancing and retracting speeds.

Presentation of the problem

The gate in a filling system for plastic pellets needs to be closed quickly. However, it should be opened slowly.

Layout

Plastic pellet filling system

Exercise 8: Actuating a shut-off device

52 © Festo Didactic GmbH & Co. KG 541088

Parameters

 A double-acting cylinder will be used.

 The closing operation should be executed by the cylinder’s forward stroke.

Project assignment

1. Describe the mode of operation of a quick exhaust valve.

2. Describe the mode of operation of a 5/2-way double pilot valve.

3. Draw a pneumatic circuit diagram for the shut-off mechanism.

4. Set up the control system.

5. Double-check the control system configuration.

6. Describe the mode of operation of the control system.

7. Create an equipment list.

Procedure

1. A shut-off mechanism (ball valve) is opened slowly after activating a pushbutton.

2. The shut-off mechanism is closed quickly after activating a second pushbutton.

Safety note

Limit pressure at the service unit to a maximum of 3.5 bar (350 kPa) for this exercise.

Exercise 8: Actuating a shut-off device

Mode of operation of a quick exhaust valve

2

1 3

1 2

3

Circuit symbol and schematic diagram of a quick exhaust valve

– Describe the mode of operation of a quick exhaust valve.

Increased piston speeds during the return stroke can be achieved with single and double-acting cylinders using quick exhaust valves, because flow resistance is thus reduced for the exhaust air.

Compressed air flows from the pilot valve to the cylinder via the quick exhaust valve. Exhaust port 3 is closed at this time.

When pressure at port 1 drops, exhaust flow occurs from 2 to 3. In order to implement optimised quick exhaust, the valve must be connected directly to the cylinder’s supply port.

Exercise 8: Actuating a shut-off device

54 © Festo Didactic GmbH & Co. KG 541088

Mode of operation of a 5/2-way double pilot valve

2 3

5

14 4 1 12

Schematic diagram of a 5/2-way double pilot valve

– Explain the mode of operation of the 5/2-way double pilot valve.

A 5/2-way double pilot valve has 5 working ports and 2 switching positions. The valve is equipped with a latching function; a short signal (pulse) suffices for reversal.

The valve piston is moved to the opposite switching position by means of a compressed air pulse at one of the two pilot ports (12/14). The valve piston is held in this position by the compressed air at the working port until a compressed air pulse at the other side of the valve reverses the valve back to its previous position. If signals are present at both pilot ports, the first signal to arrive is dominant.

A pneumatic signal at pilot port 12 causes flow from port 1 to port 2. A pneumatic signal at pilot port 14 causes flow from port 1 to port 4.

– Describe the performance of the valve depicted above when port 14 is briefly pressurised with compressed air.

When port 14 is pressurised, the valve piston is moved to the right and directs compressed air from port 1 to port 4. Port 2 is exhausted via port 3. When port 14 is once again unpressurised, the valve position remains in this position by compressed air from port 1.

Exercise 8: Actuating a shut-off device

Complete the circuit diagram

– Complete the circuit diagram shown below.

1A1

Exercise 8: Actuating a shut-off device

56 © Festo Didactic GmbH & Co. KG 541088

Sequence description

– Set up the control system and describe its working sequence.

Initial position

The piston’s initial position should be the retracted end position. The piston chamber is exhausted via 5/2-way double pilot valve 1V1 and the piston rod chamber is pressurised. If the piston is in the advanced end position, it has to be moved to the retracted end position by actuating 1S2.

Step 1-2

After actuating 3/2-way valve 1S1, the 5/2-way double pilot valve is reversed and the cylinder’s piston chamber is pressurised via the one-way flow control valve. The double-acting cylinder travels to its advanced end position. The piston rod chamber is vented via the quick exhaust valve. The piston remains in this end position, even when 1S1 is released again.

Step 2-3

The 5/2-way double pilot valve is reversed by actuating 3/2-way valve 1S2. The cylinder’s piston rod chamber is pressurised via the quick exhaust valve. The cylinder’s piston chamber is exhausted via the one-way flow control valve and the 5/2-way double pilot valve. The cylinder travels to its retracted end position.

Retracting time

The required retraction time is adjusted using the one-way flow control valve. Use a stopwatch to this end. This setting can be secured with the lock nut.

Exercise 8: Actuating a shut-off device

Create an equipment list

In addition to the circuit diagram, complete project documentation also includes an equipment list.

– Create an equipment list by entering the required components to the table below.

Quantity Designation

1 Cylinder, double-acting

1 One-way flow control valve

1 Quick exhaust valve

1 Pressure gauge

1 5/2-way double pilot valve

2 3/2-way valve with pushbutton, normally closed

1 Distributor block

1 On-off valve with filter regulator

1 Compressed air source

Exercise 8: Actuating a shut-off device

58 © Festo Didactic GmbH & Co. KG 541088