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Gate Control Valve
At present mainly three types of valves are used as control valves as listed below.
1. Globe Valve - These are typically from 1/2" to 16".
2. Ball Valves - These are typically from 2" to 24".
3. Butterfly - These are typically from 2" to 72".
Other available types are Saunders, Pinch etc.
Ball and butterfly valves are high recovery type of valves, having lower pressure drops and higher flow rates. Ball valves are normally used in paper applications, typically for pulp flow. Butterfly valves are used where low pressure drops are available and the flow required is comparatively higher. These type of valves are more prone to cavitation/flashing. All characteristics are also not available. Therefore they have limited applications in process control and used normally when globe valves are not available due to size limitations.
The most commonly used valve is the globe valve. This has advantages like better controllability, possible tight shut off but comparatively higher pressure drops and lower flow rates. These are low pressure recovery valves and therefore they are less susceptible to cavitation/flashing. Hence they are better suited for severe service applications where higher pressure drops across the valves are required.
The characteristics available are linear, equal percentage and quick opening. Custom characteristics are also available. Due to these reasons, globe valves are used widely over preference to other types provided the sizes are suitable for the application.
The disadvantages of globe valves are relatively higher pressure drops at low flow rates. There is also a limitation on the sizes which are commercially available. Machining the seats is a complicated operation and replacing the seat is also difficult.
In industries gate valves are normally used as an on-off device, which is either opened fully to allow flow through it or is shut fully to prevent the fluid flow. The valve can be opened or closed either using a hand wheel or an actuator. It is possible to open or close the valve from a remote location if a pneumatic or electrical actuator is used to operate the valve. The gate valve can be modified suitably to achieve either linear or equal percentage or any custom built characteristics so that it can function as a control valve. It is assumed that a pneumatic or electrical actuator will be used for remote positioning of the valve.
It is also possible to change the rangeability, ( i.e. the Ratio of maximum to minimum controllable flow), of the valve by suitably changing the minimum possible flow through the valve.
The gate valves as in this invention can be made available in sizes from 2" to 48" and still as effective as the conventional globe valves . The gate valves under the invention are less susceptible to cavitation/flashing.
The major application is a shutdown application. In long pipe lines if due to some reason shutdown occurs, a surge can take place which can damage the piping and other components. Gate valves with suitably machined seats can be used to limit the rate of decrease of flow to control the surge. These valves can be custom built for specific applications.
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1. Globe Valve - These are typically from 1/2" to 16".
2. Ball Valves - These are typically from 2" to 24".
3. Butterfly - These are typically from 2" to 72".
Other available types are Saunders, Pinch etc.
Ball and butterfly valves are high recovery type of valves, having lower pressure drops and higher flow rates. Ball valves are normally used in paper applications, typically for pulp flow. Butterfly valves are used where low pressure drops are available and the flow required is comparatively higher. These type of valves are more prone to cavitation/flashing. All characteristics are also not available. Therefore they have limited applications in process control and used normally when globe valves are not available due to size limitations.
The most commonly used valve is the globe valve. This has advantages like better controllability, possible tight shut off but comparatively higher pressure drops and lower flow rates. These are low pressure recovery valves and therefore they are less susceptible to cavitation/flashing. Hence they are better suited for severe service applications where higher pressure drops across the valves are required.
The characteristics available are linear, equal percentage and quick opening. Custom characteristics are also available. Due to these reasons, globe valves are used widely over preference to other types provided the sizes are suitable for the application.
The disadvantages of globe valves are relatively higher pressure drops at low flow rates. There is also a limitation on the sizes which are commercially available. Machining the seats is a complicated operation and replacing the seat is also difficult.
In industries gate valves are normally used as an on-off device, which is either opened fully to allow flow through it or is shut fully to prevent the fluid flow. The valve can be opened or closed either using a hand wheel or an actuator. It is possible to open or close the valve from a remote location if a pneumatic or electrical actuator is used to operate the valve. The gate valve can be modified suitably to achieve either linear or equal percentage or any custom built characteristics so that it can function as a control valve. It is assumed that a pneumatic or electrical actuator will be used for remote positioning of the valve.
It is also possible to change the rangeability, ( i.e. the Ratio of maximum to minimum controllable flow), of the valve by suitably changing the minimum possible flow through the valve.
The gate valves as in this invention can be made available in sizes from 2" to 48" and still as effective as the conventional globe valves . The gate valves under the invention are less susceptible to cavitation/flashing.
The major application is a shutdown application. In long pipe lines if due to some reason shutdown occurs, a surge can take place which can damage the piping and other components. Gate valves with suitably machined seats can be used to limit the rate of decrease of flow to control the surge. These valves can be custom built for specific applications.
back...