WHAT ARE VALVES
Valves are mechanical devices that controls the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries etc.
Different types of valves are available: Gate valve, Globe valve, Plug valve, Ball valve, Check valve, butterfly vales etc. Each of these types has a number of models, each with different features and functional capabilities. Some valves are self-operated while others manually or with an actuator or pneumatic or hydraulic is operated.
TYPES OF VALVES
Ball valves are quarter-turn, straight-through valves that have around closure element with matching rounded seats that permit uniform sealing stress. The valve gets its name from the ball that rotates to open and close the valve. Ball valves are used in situations where tight shut-off is required. They are wide duty valves, able to transfer gases, liquids, and liquids with suspended solids (slurries).
FEATURES OF BALL VALVES
Ball valves are used in opening or closing position, not recommended for intermediate positions. Unlike Gate valves, Ball valves are quarter-turn valves whose closing element rotates very quickly from the fully open to fully closed position.
- Low cost
- High Capacity
- Bidirectional cut
- Circulation in straight line
- Few leaks
- It cleans itself
- For driving and cutting duty, no strangulation
- When quick opening is required
- For moderate temperatures
- When minimal resistance to circulation is needed
- Low maintenance
- It does not require lubrication
- Compact Size
- Tight shut off with low torque
A plug valve is shaped like a cylinder or cone and can be rotated inside the valve body to control flow of fluids. Plug valves have one or more hollow passageways often placed horizontally to allow ease of flow through the valve when open. The most common type of plug valve is the 2 port model with an open and closed position. The two ports are usually located on opposite sides of the valve with one passageway leading from inbound to outbound and the stem and handle located on the top. A plug valve also uses a quarter turn valve, which is useful where the quick and frequent operation is essential. The valve ends can be flanged, hub type, or butt weld.
FEATURES OF PLUG VALVE
Plug valves are ¼ turn, which controls the circulation by means of a cylindrical or conical plug which has a hole in the center, taht can be moved from the open position to the closed by a turn of 90°
• High capacity.
• Low cost.
• Tight Shutt off.
• Fast operation
• Service with total opening or total closing.
• For frequent operation.
• For low pressure drop.
• For minimum resistance to circulation.
• For minimum amount of fluid trapped in the pipe.
A globe valve is a linear motion valve used to stop, start, and regulate the fluid flow. The globe valve disk can be removed entirely from the flow path, or it can completely close the flow path. During opening and closing of globe valve, disc moves perpendicularly to the seat.
FEATURES OF GLOBE VALVE
Because of their configuration, golbe valves are perfect for regulating or limiting fluid. Depending on system needs, design or position, they could generate different load losses on the line. A globe valve is multiturn, in which the closure is achieved by means of a disc or plug that cuts the passage of fluid in a seat that is usually parallel to the circulation in the pipe.
- Efficient strangulation with minimal stretching or erosion of the disc or seat
- Short stroke of the disc and few turns to operate them, which reduces time and wear on the stem and bonnet
- Precise control
- Available with multiple drills.
- Strangulation or regulation of circulation
- For frequent drive operation
- For positive cutting of gases or air
- When some resistance to circulation is acceptable..
Gate valves are designed for fully open or fully closed service. They are installed in pipelines as isolating valves, and should not be used as a control or regulating valves. Operation of a gate valve is performed doing an either clockwise to close (CTC) or clockwise to open (CTO) rotating motion of the stem. When operating the valve stem, the gate moves up- or downwards on the threaded part of the stem.
Gate valves are often used when minimum pressure loss and a free bore is needed. When fully open, a typical gate valve has no obstruction in the flow path resulting in a very low-pressure loss, and this design makes it possible to use a pipe-cleaning pig. A gate valve is a multiturn valve meaning that the operation of the valve is done by means of a threaded stem. As the valve has to turn multiple times to go from open to closed position, the slow operation also prevents water hammer effects.
FEATURES OF GATE VALVE
Gate valves can be used in many applications. They allow the fluid to flow in a fully open position and be restricted in the fully closed position, with minimal load losses. Not recommended for intermediate positions.
Gate valves are bidirectional and can be installed horizontally or vertically.
- Tight Shutt-off
- High capacity
- Low cost
- Simple design & operation
- Low resistance to circulation
- Service with total opening or total closing, no strangulation
- For infrequent use
- For mínimum resistance to circulation
- For minimal ammounts of fluid or liquid trapped in the pipe
A butterfly valve is a flow regulating disc valve. A butterfly valve consists of a circular disc or plate built with a stem through the middle or attached offset. When opened, the disc pivots 90 degrees in the valve bore, aligning with the flow, creating a nearly unrestricted flow path. Butterfly valves operate similarly to ball valves in their 90-degree rotation and allow for quick shutoff.
FEATURES OF BUTTERFLY VALVE
Butterfly valves inherently have a linear characteristic and in most applications have a useable controllable range between 25 percent and 50 percent of valve travel. They generally have a very high gain at low travel, which means that for a very small change in input signal there is a very large change in output.
Easy and fast-opening – One of the major advantages of using butterfly valves is that it offers complete closure or opening of the valve. The function can further be simplified by using a gearbox which can be attached to the stem of the valve.
Compact Design – Due to the compact design, butterfly valve designs do not require much space when compared with the other types of valves.
Better reliability– Butterfly valves are well-accepted by various industries because it needs reduced maintenance. It has a longer life than other types of valves and therefore the direct operating cost is reduced.
The valve that used to prevent backflow in a piping system is known as a check valve. It is also known as a non-return valve or NRV. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve. It allows full unobstructed flow and automatically shuts as pressure decreases. The exact operation will vary depending on the mechanism of the valve.
FEATURES OF CHECK VALVE
Check valves are automatic valves, which have safety applications to prevent flow returns and reduce water hammer. When the pump isn’t working, they keep the pipe line full.
- Minimum disk stroke to fully open position
- Rapid action
- When there are frequent circulation changes in the pipe
- For use with globe and angular valves
- For use when the pressure drop through the valve is no problem
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