2. I NTRODUCTION A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Depending on the valve function, its function may be manually initiated or may be automatically initiated by signal from control device or the valve may automatically respond to changing system condition.

3. T YPES OF VALVES 1. Direction control valves 2. Direction control check valve or non return valves 3. Flow control valves 4. Pressure control valves

4. D IRECTION CONTROL VALVE Direction control valves are used to control the flow of fluid in a desired direction and location in the circuit. Directional Control Valve is characterized by number of controlled connections or way, the number of switching positions and the method of actuation.

5. C ATEGORIZATION ON BASIS OF DESIGN DCVSlide valveslongitudinal Longitudinal flat platePoppet valveBall seatDisc seat

6. P OPPET VALVES A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapour flow into an engine. It consists of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem

7. S LIDE VALVES Slide valves were commonly used in steam engines to control the flow of steam in and out of the engine. The valves slid from side to side in time with the other moving parts to allow steam to enter the engine and the exhaust to exit through the ports, or openings.

8. When the slide valve slides to one side, it uncovers the intake port and allows steam to fill the cylinder. This steam pushes on the piston, found inside the cylinder, and the piston in turn pushes on a rod that turns the flywheel. The flywheel turns to create motion so the steam engine can move. When the slide valve slides to the opposite side, it opens the exhaust port and releases the steam while the piston slides back and the process starts over again.

9. C LASSIFICATION ON BASIS OF NUMBER OF PORTS AND SWITCHING POSITION 2/2, 3/2, 4/2, 5/2, 5/3 The first digit of a valve designation shows the number of ports. The second digit shows the number of possible switching positions

10. 4/2 WAY VALVE Red lines represent 4 ports Arrow show direction of flow 1 2 (Fig. 1)(Fig. 2)

11. 4/2 WAY VALVE (Fig.3)(Fig.4)

12. 5/2 WAY VALVE R P S B A R P S B A

13. 5/2 WAY VALVE In this position, pressure is allowed from P to B. Exhaust from A to S. In this position, pressure is allowed from P to A. Exhaust from B to R.