ATM 1132 Basic Pneumatics

ATM 1132–Basic Pneumatics

Basic Pneumatics

Module 8: Pressure control valves

PREPARED BY

Academic Services

April 2012

Module 8: Pressure control valves

Module Objectives

After the completion of this module, thestudentwill be able to:

Explain the the main types of pressure control valves.
Explain the function of each type of pressure control valves.
Describe the main parts of the pressure sequence valve.
Adjust the pressure regulator and the pressure sequence to the required pressure.
Draw the required circuit diagram.
Simulate the pneumatic circuit using FluidSIM software.
Explain the difference between the pressure limiting valve and the pressure sequence valve.

Module Contents

Topic / Page No.
1 / Main types of pressure valves / 3
2 / Pressure limiting valve / 3
3 / Pressure regulating valve / 4
4 / Pressure sequence valve / 5
5 / Practical task 1 (Pressure dependent control) / 6
6 / Practical task 2 (Foil welding drum) / 8
7 / Supplementary resources / 10
8 / References / 10
9 / Worksheet / 12
1-Introduction
Pressure control valves are elements which influence the pressure or are controlled by the magnitude of the pressure. They are used to limit the maximum pressure in the circuit, reduce the pressure to a required value or open the flow when the pressure reaches a certain value.
2-Main types of the pressure valves
Pressure valves are divided into three groups:
1-Pressure limiting valves
2-Pressure regulating valves
3-Pressure sequence valves
2.1-Pressure Limiting valve
The pressure limiting valve is used mainly as safety valve (pressure relief valve). It prevents the maximum permissible pressure in a system from being exceeded.
If the maximum pressure has been reached at the valve inlet, the valve outlet is opened and the excess air pressure exhausts to atmosphere.
The valve remains open until it is closed by the built-in spring after reaching the preset system pressure.
The pressure relief valve is used to control and limit the maximum pressure in the air tank. When the set pressure is reached, the pressure relief valve opens and the air is exhausted to atmosphere. A non return valve prevents the emptying of the tank.
Fig. 8.1 a and b show some pictures for the valve, and Fig. 8.1 c shows the ISO symbol. /
(a)

(b)

(c)
Fig. 8.1:Pressure limiting valve
2.2-Pressure regulating valve
The pressure regulating valve maintains the working pressure largely constant,irrespective of pressure fluctuations in the system and air consumption.
The pressure regulator adjusts the supply of compressed air to the operating pressure and compensates any pressure fluctuations. The direction of flow is indicated by arrows on the housing.
The input pressure must always be higher than the working pressure.
The pressure regulator with pressure gauge and push-in elbow fittings is screwed onto a function plate. The unit is slotted into the profile plate via a quick release detentsystem with blue lever.
The pressure gauge indicates the pressure set.
The pressure regulator is fitted with an adjusting knob, which can be turned to setthe required pressure. By sliding the adjusting knob towards the housing, thesetting can be locked.
Fig. 8.2 a shows the picture of the valve and Fig. 8.2 b shows the ISO symbol. Whereas Fig. 8.2 c shows a cross section in the valve. /
(a)

(b)

(c)
Fig. 8.2:Pressure regulating valve
2.3-Pressure sequence valve
A sequence valve is somewhat similar to arelief valve except that, after the set pressure hasbeen reached, the sequence valve diverts the fluidto a secondactuator or motor to do work.
The pressure sequence valve is screwed on to a function plates, which includes therequired push-in fittings. The unit is mounted on the profile plate via a quick releasedetent system with blue lever.
The pressure sequence valve is reversed once the pilot pressurehas been reached at port 12, and switched to the initial position via return springafter the signal has been removed. The pressure of the control signal is infinitelyadjustable by means of a pressure adjustment screw.

If the pressure at pilot port 12 exceeds a specific, adjustable value, the actuated 3/2way valve switches; pressure is applied at working port 2.
The 3/2-way valve reverses, if the pressure at pilot port falls below the set value.

Uses
A pressure dependent signal is required to enable the next step in a control system.Example: Clamping pressure of a cylinder.
Fig. 8.3 a shows the picture of the valve and Fig. 8.3 b shows the ISO symbol. Whereas Fig. 8.3 c shows a cross section in the valve. /
(a)

(b)

(c)
Fig. 8.3:Pressure sequence valve

3- Practical Task 1: Pressure dependent control

3.1Learning objectives:

Upon the completion of this task, thestudentwill be

•Familiar with indirect actuation of a double acting cylinder with a double pilot valve.

•Able to use and adjust the pressure sequence valve.

3.2 Task description:

A plastic component is embossed using a die driven by a double-actingcylinder. The die is to advance and emboss the plastic when a pushbutton is operated. The return of the die is to be effected when a preset pressure is reached. The embossing pressure is to be adjustable.

Fig. 8.4 Positional sketch

3.3 Task requirements:

Draw pneumatic circuit diagram
Simulate the circuit using FluidSIM software.
Assemble the circuit practically and check its operation.

Draw the pneumatic circuit here

4- Practical Task2: Foil welding drum

4.1Learning objectives:

Upon the completion of this task, thestudentwill be

•Familiar with indirect actuation of a double acting cylinder with a double pilot valve.

•Able to operate a pressure regulator to limit the piston force.

•Able to use and adjust the pressure sequence valve.

4.2 Task description:

An electrically heated welding rail is pressed onto a rotatable cold drumby a double-acting cylinder (1A) and welds a continuous plastic sheetinto pieces of tubing. The forward stroke is triggered by means of a pushbutton. The maximum cylinder force is set at 4 bar (= 400 kPa) via apressure regulator with pressure gauge. (This prevents the welding raildamaging the metal drum.)

The return stroke is not initiated until theforward end position has been reached and the pressure in thepiston area has reached 3 bar (= 300 kPa).The supply air is restricted for the movement of the cylinder.

Fig. 8.6 Positional sketch

4.3 Task requirements:

Draw pneumatic circuit diagram
Simulate the circuit using FluidSIM software.
Assemble the circuit practically and check its operation.

Draw the pneumatic circuit here
5. For further reading, you can use the following links:
1- Supplementary recourses

Pneumatics video from Festo.
FluidSIM software.

7. References
1-Festo manuals and workbook TP101
2-Festo manuals and textbook TP101
Student’s notes
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Worksheet 1

Draw the symbol of pressure sequence valve

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Draw the symbol of 5/2 way, double pilot valve

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Draw the symbol of pressure regulator

What is the function of pressure limiting valve?

What is the function of pressure regulating valve?

What is the function of pressure sequence valve?

Module 8: Pressure control valves 1