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.
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 of Butterfly valve:
- Resilient butterfly valve: It has a flexible rubber seat. Working pressure 232 psi
- High performance butterfly valve: It is usually double eccentric in design. Working pressure up to 725 psi.
- 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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