What is a valve?
In the fluid piping system, a valve is a control element whose main function is to isolate the equipment and the piping system, adjust the flow, prevent backflow, adjust and release the pressure. It can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal, and radioactive media. Since it is very important to choose the most suitable valve for the piping system, it is also important to know the characteristics of the valve, the steps, and the basis for selecting the valve.
Classifications of valves
1. A valve can be divided into two categories:
The first type is the automatic valve that relies on the media (liquid or gas), such as check valves, safety valves, regulating valves, traps, pressure reducing valves, etc.
The second type is the actuated valve which is operated manually, electrically, hydraulically, and pneumatically, such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc.
2. According to the structural characteristics, the direction in which the closure member moves relative to the valve seat, a valve can be divided into the following:
(1) Valves whose closing part moves along the center of the valve seat.
(2) The closing part moves along the center of the vertical valve seat.
(3) A valve whose closing part is a plunger or a ball, which rotates around its centerline.
(4) A valve whose closing part rotates around the axis outside the valve seat.
(5) A valve whose closing part rotates around the axis in the valve seat.
(6) The closing part slides in the direction perpendicular to the channel.
3. A valve can be divided into the following kinds according to the different uses:
(1) Connecting and cutting off: valves use to connect or cut off media in the pipeline, such as globe valves, gate valves, ball valves, butterfly valves, etc.
(2) Preventing back flows: valves use to prevent the medium from flowing back, for example, a check valve.
(3) Regulating: valves use to regulate the pressure and flow of the medium, such as regulating valves and pressure reducing valves.
(4) Distributing: valves use to change the flow direction of the medium and distribute the medium, such as three-way plug valves, distribution valves, slide valves, etc.
(5) Safety: when the medium's pressure exceeds the specified value, valves are used to discharge excess medium to ensure the safety of the piping system and equipment, such as safety valves and emergency valves.
(6) Other special purposes: traps, vent valves, drain valves, etc.
4. A valve can be divided into the following types according to the driving modes:
(1) Manual valves: they are operated by handwheels, handles, levers, sprockets, etc. They are driven by the human driving force, and the great transmission torque is equipped with worm gears, gears, and other speed reduction devices.
(2) Electric valves: they are driven by a motor or other electrical devices.
(3) Hydraulic valves: they are driven by water or oil.
(4) Pneumatic valves: they are driven by compressed air.
5. A valve can be classified into the following kinds based on the nominal pressure of the valve:
(1) Vacuum valves: the absolute pressure is less than 0.1Mpa, that is, the valve with 760 mm mercury column. Usually, the pressure is expressed by the mercury column or water column.
(2) Low pressure valves: valves has nominal pressure PN less than or equal to 1.6Mpa, including steel valves with PN less than or equal to 1.6MPa.
(3) Medium pressure valves: a valve has nominal pressure between 2.5 and 6.4MPa.
(4) High pressure valves: a valve has nominal pressure from 10.0 to 80.0MPa.
(5) Ultra-high pressure valves: a valve has a nominal pressure greater than or equal to 100.0MPa.
6. A valve can be divided into the following kinds based on the temperature of the medium:
(1) Ordinary valves: they are suitable for medium temperatures of -40°C to 425°C.
(2) High temperature valves: medium temperatures of them are between 425°C and 600°C.
(3) Heat-resistant valves: they are good for valves whose medium temperature is above 600℃.
(4) Low temperature valves: they are suitable for valves with medium temperatures between -150℃ and -40℃.
(5) Ultra-low temperature valves: they are valves whose medium temperature is below -150℃.
In the fluid piping system, a valve is a control element whose main function is to isolate the equipment and the piping system, adjust the flow, prevent backflow, adjust and release the pressure. It can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal, and radioactive media. Since it is very important to choose the most suitable valve for the piping system, it is also important to know the characteristics of the valve, the steps, and the basis for selecting the valve.
Classifications of valves
1. A valve can be divided into two categories:
The first type is the automatic valve that relies on the media (liquid or gas), such as check valves, safety valves, regulating valves, traps, pressure reducing valves, etc.
The second type is the actuated valve which is operated manually, electrically, hydraulically, and pneumatically, such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc.
2. According to the structural characteristics, the direction in which the closure member moves relative to the valve seat, a valve can be divided into the following:
(1) Valves whose closing part moves along the center of the valve seat.
(2) The closing part moves along the center of the vertical valve seat.
(3) A valve whose closing part is a plunger or a ball, which rotates around its centerline.
(4) A valve whose closing part rotates around the axis outside the valve seat.
(5) A valve whose closing part rotates around the axis in the valve seat.
(6) The closing part slides in the direction perpendicular to the channel.
3. A valve can be divided into the following kinds according to the different uses:
(1) Connecting and cutting off: valves use to connect or cut off media in the pipeline, such as globe valves, gate valves, ball valves, butterfly valves, etc.
(2) Preventing back flows: valves use to prevent the medium from flowing back, for example, a check valve.
(3) Regulating: valves use to regulate the pressure and flow of the medium, such as regulating valves and pressure reducing valves.
(4) Distributing: valves use to change the flow direction of the medium and distribute the medium, such as three-way plug valves, distribution valves, slide valves, etc.
(5) Safety: when the medium's pressure exceeds the specified value, valves are used to discharge excess medium to ensure the safety of the piping system and equipment, such as safety valves and emergency valves.
(6) Other special purposes: traps, vent valves, drain valves, etc.
4. A valve can be divided into the following types according to the driving modes:
(1) Manual valves: they are operated by handwheels, handles, levers, sprockets, etc. They are driven by the human driving force, and the great transmission torque is equipped with worm gears, gears, and other speed reduction devices.
(2) Electric valves: they are driven by a motor or other electrical devices.
(3) Hydraulic valves: they are driven by water or oil.
(4) Pneumatic valves: they are driven by compressed air.
5. A valve can be classified into the following kinds based on the nominal pressure of the valve:
(1) Vacuum valves: the absolute pressure is less than 0.1Mpa, that is, the valve with 760 mm mercury column. Usually, the pressure is expressed by the mercury column or water column.
(2) Low pressure valves: valves has nominal pressure PN less than or equal to 1.6Mpa, including steel valves with PN less than or equal to 1.6MPa.
(3) Medium pressure valves: a valve has nominal pressure between 2.5 and 6.4MPa.
(4) High pressure valves: a valve has nominal pressure from 10.0 to 80.0MPa.
(5) Ultra-high pressure valves: a valve has a nominal pressure greater than or equal to 100.0MPa.
6. A valve can be divided into the following kinds based on the temperature of the medium:
(1) Ordinary valves: they are suitable for medium temperatures of -40°C to 425°C.
(2) High temperature valves: medium temperatures of them are between 425°C and 600°C.
(3) Heat-resistant valves: they are good for valves whose medium temperature is above 600℃.
(4) Low temperature valves: they are suitable for valves with medium temperatures between -150℃ and -40℃.
(5) Ultra-low temperature valves: they are valves whose medium temperature is below -150℃.
(1) Valves with small diameters: valves with a nominal diameter of less than 40 mm
(2) Valves with medium diameters: valves with a nominal diameter of 50 to 300 mm
(3) Valves with large diameters: valves with a nominal diameter between 350 and 1200 mm
(4) Valves with extra large diameters: valves with a nominal diameter greater than or equal to 1400 mm
8. A valve can be divided into the following kinds according to the connection between the valve and the pipeline:
(1) Flanged valves: the valve body has a flange and is connected to the pipeline by a flange.
(2) Threaded valves: the valve body has internal threads or external threads, and the valve is connected with the pipeline by threads.
(3) Welded valves: the valve body has a welding port and is connected to the pipeline by welding.
(4) Clamped valves: there is a clamping place on a valve so that the valve can be connected to the pipe by clamping.
(5) Valves with ferrules: a valve uses ferrules to connect to the pipeline.
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