Basic Pneumatics Module 8: Pressure control valves PREPARED BY Academic Services April 2012 Applied Technology High Schools, 2012
Module 8: Pressure control valves Module Objectives After the completion of this module, the student will 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 2 Module 8: Pressure control Valves
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. (a) 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. (b) (c) Fig. 8.1:Pressure limiting valve Module 8: Pressure control valves 3
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. (a) 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 detent system with blue lever. (b) The pressure gauge indicates the pressure set. The pressure regulator is fitted with an adjusting knob, which can be turned to set the required pressure. By sliding the adjusting knob towards the housing, the setting 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. (c) Fig. 8.2:Pressure regulating valve 4 Module 8: Pressure control Valves
2.3- Pressure sequence valve A sequence valve is somewhat similar to a relief valve except that, after the set pressure has been reached, the sequence valve diverts the fluid to a second actuator or motor to do work. The pressure sequence valve is screwed on to a function plates, which includes the required push-in fittings. The unit is mounted on the profile plate via a quick release detent system with blue lever. The pressure sequence valve is reversed once the pilot pressure has been reached at port 12, and switched to the initial position via return spring after the signal has been removed. The pressure of the control signal is infinitely adjustable 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 Module 8: Pressure control valves 5
3- Practical Task 1: Pressure dependent control 3.1 Learning objectives: Upon the completion of this task, the student will 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-acting cylinder. The die is to advance and emboss the plastic when a push button 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 6 Module 8: Pressure control Valves
3.3 Task requirements: 1. Draw pneumatic circuit diagram 2. Simulate the circuit using Fluid SIM software. 3. Assemble the circuit practically and check its operation. Draw the pneumatic circuit here Module 8: Pressure control valves 7
4- Practical Task 2: Foil welding drum 4.1 Learning objectives: Upon the completion of this task, the student will 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 drum by a double-acting cylinder (1A) and welds a continuous plastic sheet into pieces of tubing. The forward stroke is triggered by means of a push button. The maximum cylinder force is set at 4 bar (= 400 kpa) via a pressure regulator with pressure gauge. (This prevents the welding rail damaging the metal drum.) The return stroke is not initiated until the forward end position has been reached and the pressure in the piston area has reached 3 bar (= 300 kpa).the supply air is restricted for the movement of the cylinder. Fig. 8.6 Positional sketch 8 Module 8: Pressure control Valves
4.3 Task requirements: 1. Draw pneumatic circuit diagram 2. Simulate the circuit using FluidSIM software. 3. Assemble the circuit practically and check its operation. Draw the pneumatic circuit here Module 8: Pressure control valves 9
5. 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 6. Supplementary recourses 1. Pneumatics video from Festo. 2. FluidSIM software. 7. References 1- Festo manuals and workbook TP101 2- Festo manuals and textbook TP101 10 Module 8: Pressure control Valves
Student s notes Module 8: Pressure control valves 11
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? 12 Module 8: Pressure control Valves