Valves are fluid power control elements used for controlling and regulating the working medium z e compressed air in the pneumatic system and oil in the hydraulic system. Valves are used to
1. Start and stop pneumatic and hydraulic energy
2. Control the direction of flow of compressed air
3. Control the pressure rating of compressed air.
Fluid power control elements may be divided into four broad groups
1. Directional control valve
2. Directional control check valves
3. Flow control valve
4. Pressure control valve
Directional control valve: These valves are used mainly to direct the flow of the pressure fluid in the desired directions.
The main function and their ISO symbols are given below (Pneumatic)
Table: Value Symbols, Description and Main Application
2. Direction control check valve
– Check valves are termed as non return valves. Its function is to allow the flow of fluid in one direction only. Spring operated check valve as shown in figure.
Flow control valve: These valves are used to control the speed of pneumatic actuators. This is done by constricting or throttling a flow passage so that a part of supply is obstructed in the area of construction. There are two types of flow control valves.
1. Fixed flow control
2. Variable flow control
Figure shows a non return type variable flow control valve
Fig. Non-return type flow control valve
1. A—B free flow of air 2. B—A restricted flow of air
Pressure control valve: These valves are used for regulating the pressure of fluids in a fluid system Pressure relief valve, regulating valves comes under this category.
Pressure regulation valve: The main function of this valve is to regulate the incoming pressure to the system so that the desired air pressure is capable of flowing at a steady condition.
Fig. pressure regulator