In the fluid piping system, the valve is the control element, and its main function is to isolate the equipment and the piping system, adjust the flow, prevent backflow, adjust and drain 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. Because it is very important to choose the most suitable valve for the piping system, it is also important to understand the characteristics of the valve and the steps and basis for selecting the valve.
Valve classification
1. The valve can be divided into two categories:
The first type of automatic valve: a valve that relies on the ability of the medium (liquid, gas) to act on its own.
Such as check valves, safety valves, regulating valves, traps, pressure reducing valves, etc. To
The second type of drive valve: a valve that is operated manually, electrically, hydraulically, and pneumatically.
Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, plug valve, etc.
2. According to the structural characteristics, according to the direction in which the closing member moves relative to the valve seat, it can be divided into:
1. Sectional door shape: the closing part moves along the center of the valve seat;
2. Gate shape: the closing part moves along the center of the vertical valve seat;
3. Cock and ball: the closing part is a plunger or a ball, which rotates around its own centerline;
4. Swing shape: the closing part rotates around the axis outside the valve seat;
5. Dish shape: the disc of the closing part, which rotates around the axis in the valve seat;
6. Slide valve shape: The closing piece slides in the direction perpendicular to the channel.
Three, according to the purpose, according to the different purposes of the valve can be divided into:
1. For breaking: used to connect or cut off pipeline media, such as globe valves, gate valves, ball valves, butterfly valves, etc. …
2. Check use: used to prevent the medium from flowing back, such as a check valve. …
3. Adjustment: used to adjust the pressure and flow of the medium, such as regulating valves and pressure reducing valves. …
4. Distribution: used to change the flow direction of the medium and distribute the medium, such as three-way cock, distribution valve, slide valve, etc. To
5. Safety valve: When the pressure of the medium exceeds the specified value, it is used to discharge excess medium to ensure the safety of the pipeline system and equipment, such as safety valves and emergency valves.
6. Other special purposes: such as traps, vent valves, drain valves, etc.
4. According to the driving mode, it can be divided into different driving modes:
1. Manual: With the help of handwheel, handle, lever or sprocket, etc., it is driven by manpower, and the transmission torque is equipped with worm gear, gear and other speed reduction devices. …
2. Electric: driven by a motor or other electrical devices. …
3. Hydraulic: driven by (water, oil). …
4. Pneumatic: driven by compressed air.
5. According to the pressure, it can be divided according to the nominal pressure of the valve:
1. Vacuum valve: a valve with an absolute pressure of <0.1Mpa that is 760mm mercury column height, usually expressed in mm mercury column or mm water column. …
2. Low pressure valve: valves with nominal pressure PN≤1.6Mpa (including steel valves with PN≤1.6MPa)
3. Medium pressure valve: a valve with a nominal pressure of PN2.5—6.4MPa. …
4. High-pressure valve: a valve with a nominal pressure of PN10.0-80.0MPa. …
5. Ultra-high pressure valve: a valve with a nominal pressure of PN≥100.0MPa.
Six, according to the temperature of the medium, according to the temperature of the medium when the valve is working, it can be divided into:
1. Ordinary valve: suitable for valves with medium temperature -40℃～425℃. …
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 medium temperature above 600℃. …
4. Low temperature valve: suitable for valves with medium temperature -150℃～-40℃. …
5. Ultra-low temperature valve: suitable for valves whose medium temperature is below -150℃.
Seven, according to the nominal diameter, according to the nominal diameter of the valve can be divided into:
1. Small diameter valve: the valve with nominal diameter DN<40mm. …
2. Medium-caliber valves: valves with a nominal diameter of DN50～300mm. …
3. Large diameter valves: valves with a nominal diameter of DN350～1200mm. …
4. Extra large diameter valves: valves with nominal diameter DN ≥ 1400mm.
8. According to the connection with the pipeline, it can be divided according to the connection between the valve and the pipeline:
1. Flange connection valve: The valve body has a flange and is connected to the pipeline by flange. …
2. Threaded connection valve: the valve body has internal or external thread, and the valve is connected with the pipeline by thread. …
3. Welding connection valve: The valve body has a welding port and is connected to the pipeline by welding. …
4. Clamping clamp connection valve: a valve with clamps on the valve body and clamp connection with the pipeline. …
5. Card sleeve connection valve: the valve is connected with the sleeve and pipe.
Valve characteristics
There are generally two types of valve characteristics, use characteristics and structural characteristics.
Use characteristics: It determines the main performance and scope of use of the valve. The characteristics of the valve are: valve category (closed circuit valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.); Material of the main parts of the valve (valve body, bonnet, valve stem, valve disc, sealing surface); valve transmission mode, etc.
Structural characteristics: It determines some structural characteristics of the valve installation, repair, maintenance and other methods. The structural characteristics include: the structural length and overall height of the valve, and the connection form with the pipeline (flange connection, thread connection, clamp connection, External thread connection, welding end connection, etc.); the form of the sealing surface (inlay ring, thread ring, surfacing, spray welding, valve body); valve stem structure (rotating rod, lifting rod), etc.
Steps and basis for selecting valves
Selection steps:
1. Clarify the purpose of the valve in the equipment or device, and determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc.
2. Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.
3. Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electrohydraulic linkage, etc.
4. Determine the material of the selected valve housing and internal parts according to the medium, working pressure and working temperature conveyed by the pipeline: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy
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