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Valves



Valves

A valve is a device that regulates the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.
Valves are used in a variety of contexts, including industrial, military, commercial, residential, and transport. There are many types of valves such as gate valve, glove valve, angle valve, automatic stop valve, cheek valve, back pressure valve, butterfly valve, diaphragm valve etc.
Valve materials:
Ø  For larger size cast iron or cast steel or forged steel is used.
Ø  For valves seats, discs and spindles brass is used.
1.      Gate valve, Glove valve, Angle valve, Automatic stop valve etc are called normally stop valve because they are used to stop the flow of fluids.
2.      Reducing valve: The function of reducing valve is to change pressure in a steam line.
3.      Check valve: Check valve permits the flow in one direction.
4.      Back pressure valve: It is used in connection with the exhaust piping of the engine to permit underused in pressure.

See full size image
                            See full size image                                          
Hydraulic flow control valve                 Cheek valve                               Gate valve
                                   
                                     Figure: Various flow control valves
Butterfly valve:
            A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve designs as well as being lighter in weight, meaning less support is required. The disc is positioned in the center of the pipe, passing through the disc is a rod connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow therefore a pressure drop is always induced in the flow, regardless of valve position.
Types:
  1. Resilient butterfly valve: It has a flexible rubber seat. Working pressure 232 psi
  2. High performance butterfly valve: It is usually double eccentric in design. Working pressure up to 725 psi.
  3. Tricentric butterfly valve: It is usually with metal seat in design. Working pressure up to 1450 psi.
                                                   
                         Figure: Butterfly valve                   Figure: Diaphragm valve

Diaphragm valve:
Diaphragm valve consists of a valve body with two or more ports, a diaphragm, and a "saddle" or seat upon which the diaphragm closes the valve. The valve is constructed from either plastic or steel.
There are two main categories of diaphragm valves: one type seals over a "weir" (saddle) and the other (sometimes called a "straight-way" valve) seals over a seat. The main difference is that a saddle-type valve has its two ports in line with each other on the opposite sides of the valve, whereas the seat-type has the in/out ports located at a 90 degree angle from one another. The saddle type is the most common in process applications and the seat-type is more commonly used as a tank bottom valve but exists also as a process valve
Diaphragm valves can be manual or automated. Their application is generally as shut-off valves in process systems within the food and beverage, pharmaceutical and biotech industries.
 Body materials of diaphragm valve:
Ø  Brass
Ø  Steel (cast iron, ductile iron, carbon steel, stainless steel etc)
Ø  Plastic (PVC-U or PVC-C )

Diaphragm materials:

Ø  Natural rubber

Ø  Silicon rubber

Ø  Nitrile

Ø  Plastics

 

Advantages and disadvantages:

Types of valve

Advantages

Disadvantages

Glove valve

Better flow closed, properly flow control.

Head loss is more.

Gate valve

Laminar flow

Time required is more for closing the valve

Butterfly valve

Quick flow control, laminar flow and easy operation

Limitation of temperature

Diaphragm valve

No need of gland

Limitation of temperature and pressure

 

 



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