In the fluid pipeline system, the valve is a control element, and its main function is to isolate the equipment and the pipeline system, regulate the flow rate, prevent backflow, regulate and discharge 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 pipeline system, it is also very important to understand the characteristics of the valve and the steps and basis for selecting the valve.
Classification of valves
1. Valves can be generally divided into two categories:
The first type of automatic valve: a valve that operates by itself based on the ability of the medium (liquid, gas).
Such as check valves, safety valves, regulating valves, steam traps, pressure reducing valves, etc.
The second type of actuated valve: a valve that operates manually, electrically, hydraulically, or pneumatically.
Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, plug valve, etc.
2. According to the structural features, according to the direction in which the closing member moves relative to the valve seat, it can be divided into:
1. Cut-off shape: the closing member moves along the center of the valve seat;
2. Gate shape: the closing member moves along the center of the vertical seat;
3. Cock and ball: the closing part is a plunger or a ball, which rotates around its own center line;
4. Swing shape: the closing member rotates around the axis outside the valve seat;
5. Disk shape: the disc of the closing member, which rotates around the axis in the valve seat;
6. Slide valve shape: the closing member slides in the direction perpendicular to the channel.
3. According to the purpose, according to the different uses of the valve, it can be divided into:
1. For breaking: used to connect or cut off the pipeline medium, such as globe valve, gate valve, ball valve, butterfly valve, etc.
2. For non-return: used to prevent backflow of medium, such as check valve.
3. For adjustment: used to adjust the pressure and flow of the medium, such as regulating valves and pressure reducing valves.
4. For distribution: used to change the flow direction of the medium and distribute the medium, such as three-way cocks, distribution valves, slide valves, etc.
5. Safety valve: When the medium pressure exceeds the specified value, it is used to discharge excess medium to ensure the safety of the pipeline system and equipment, such as safety valve and emergency valve.
6. Other special purposes: such as steam traps, vent valves, sewage valves, etc.
4. According to the driving method, it can be divided according to different driving methods:
1. Manual: With the help of handwheels, handles, levers or sprockets, etc., it is driven by manpower. When transmitting large torque, it is equipped with reduction devices such as worm gears and gears.
2. Electric: driven by a motor or other electrical devices.
3. Hydraulic: driven by (water, oil).
4. Pneumatic: driven by compressed air.
Five, pressing force, according to the nominal pressure of the valve can be divided into:
1. Vacuum valve: absolute pressure <0.1Mpa, that is, a valve with a height of 760mm Hg, usually expressed in mm Hg or mm H2O.
2. Low pressure valve: valve with nominal pressure PN≤1.6Mpa (including steel valve with PN≤1.6MPa)
3. Medium pressure valve: a valve with nominal pressure PN2.5—6.4MPa.
4. High pressure valve: a valve with nominal pressure PN10.0—80.0MPa.
5. Ultra-high pressure valve: a valve with a nominal pressure PN≥100.0MPa.
6. According to the temperature of the medium, it can be divided according to the temperature of the medium when the valve is working:
1. Ordinary valve: suitable for valves with a medium temperature of -40°C to 425°C.
2. High temperature valve: suitable for valves with a medium temperature of 425°C to 600°C.
3. Heat-resistant valve: suitable for valves with a medium temperature above 600°C.
4. Low-temperature valve: suitable for valves with a medium temperature of -150°C to -40°C.
5. Ultra-low temperature valve: suitable for valves with a medium temperature below -150°C.
Seven, according to the nominal diameter, according to the nominal diameter of the valve can be divided into:
1. Small-diameter valves: valves with a nominal diameter of DN<40mm.
2. Medium-diameter valves: valves with a nominal diameter of DN50 to 300mm.
3. Large-diameter valves: valves with a nominal diameter of DN350-1200mm.
4. Extra-large diameter valve: a valve with a nominal diameter DN≥1400mm.
8. According to the connection method with the pipeline, it can be divided according to the connection method between the valve and the pipeline:
1. Flange connection valve: the valve body has a flange, and the valve is flanged to the pipeline.
2. Threaded connection valve: the valve body has internal or external threads, and the valve is threaded with the pipeline.
3. Welding connection valve: the valve body has a welding port and is connected to the pipeline by welding.
4. Clamp connection valve: a valve with a clamp on the valve body and connected to the pipeline with a clamp.
5. Ferrule connection valve: a valve that is connected with a ferrule and a pipeline.