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TYPES OF VALVES

Types	Advantages	Disadvantages

1. Throttling Valves

1. Diaphragm valve	The interior of this valve is very smooth, and can be easily cleaned.	The valve leaks upon the failure of the diaphragm.
2. Butterfly valve	The rubber-lined valve is a good, cheap valve for all types of low pressure, non-critical services. This valve can also be lined with a resistant polymer for very corrosive service.	Rubber lined valve has pressure limitations.
3. Needle valve	It gives good flow control; It can have very high pressure ratings.	It causes a high pressure drop & presents a greater risk of clogging due to entrained solids.
4. Pinch valve	This valve can be tightly shut off, and will even close when entrained solids are present in the flowing fluid.	The pressure rating of this valve is low. The compatibility of the hose material with the process stream is critical.
5. Globe valve	It can be used to modulate flow or to stay partially open to impose a certain pressure drop.	It passes flow in only one direction.
6. Stop check valve	Besides throttling like a globe valve, this valve also prevents reverse flow.	It's design is more complex than that of globe and check valves.
7. Angle valve	Pressure drop is slightly less than a conventional globe valve.	It complicates that piping layout.
8. Y-pattern globe valve	It can throttle and is often used in high pressure service.	It complicates the piping design.

2. On-off valves

Types	Advantages	Disadvantages
1. Ball valve	Pressure drop is very low; it is suitable for handling erosive fluids & slurries.	Fluids that set up or polymerize could freeze the ball.
2. Plug valve	Pressure drop is fairly low; lubricated type is very good for slurry and catalyst service; plastic-sleeved plug is used for highly corrosive services.	Lubricated plug valve should be lubricated every time it is operated; plastic valves have a limited operating temperature (400F)
3. Hydrant valve	Useful in freezing climates.	-------------
4. Gate valve	Pressure drop is low; this valve weighs and costs less than other comparable size valves.	It is almost completely incapable of throttling.
5. Ram valve/ Displacement valve	It is very useful for taking accurate samples of solid bearing streams.	These valves are custom designed to some exact, correct valve should be chosen for each application.

3. Non - return valves

Types	Advantages	Disadvantages
1. Split disc-check valve	It is generally the least expensive check valve in medium to large sizes. Shutoff is somewhat better in this valve.	It is not suitable for large material.
2. Lift-check valve	In small sizes, it is also one of the cheapest check valve. In large sizes, it can be used in pulsating flows.	The pressure drop is fairly high.
3. Swing-check valve	It will operate well whether installed horizontally or vertically. The body can be equipped with drain or bypass taps.	It is large & heavy compared with other types of such valves. This valve is not suitable for pulsating flows containing entrained material.
4. Tilting-disc-check valve	The pressure drop is lower than that of the swing-check valve.	IT is large & heavier than the swing-check valve. An over-sized valve is prone to flutter or slamming.

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