The key points of valve selection are summarized

The key points of valve selection are summarized

Most of the media in chemical production devices have the characteristics of high toxicity, combustible, explosive and corrosive. The working conditions are complex and harsh, and the operating temperature and pressure are high. Once the valve fails, the light will lead to medium leakage, the heavy will lead to the shutdown of the device, and even cause malignant accidents. Therefore, the scientific and reasonable choice of valve can not only reduce the construction cost of the device, but also ensure the safe operation of production. Let’s talk about valve selection!
Most of the media in chemical production devices have the characteristics of high toxicity, combustible, explosive and corrosive. The working conditions are complex and harsh, and the operating temperature and pressure are high. Once the valve fails, the light will lead to medium leakage, the heavy will lead to the shutdown of the device, and even cause malignant accidents. Therefore, the scientific and reasonable choice of valve can not only reduce the construction cost of the device, but also ensure the safe operation of production. Let’s talk about valve selection!
Key points of valve selection
1 Clear valve in equipment or device use
Determine the working conditions of the valve: the nature of the applicable medium, working pressure, working temperature and operating control mode.
Choose the right type of valve
The correct choice of valve type is based on the designer of the whole production process, the full grasp of operating conditions as a prerequisite, in the selection of valve type, the designer should first master the structural characteristics and performance of each valve.
Determine the end connection of the valve
In threaded connection, flange connection, welding end connection, the first two kinds of common. Threaded valves are mainly valves with nominal diameter below 50mm. If the diameter size is too large, the installation and sealing of the connection is very difficult.
Flanged valves are more convenient to install and remove, but they are bulkier and more expensive than threaded valves, so they are suitable for pipe connections of various sizes and pressures.
The welded connection is more reliable than the flanged connection, which is suitable for loading conditions. But the welded valve disassembly and reinstallation are more difficult, so its use is usually in long-term reliable operation, or use conditions of loading, high temperature occasions.
4. Selection of valve material
The choice of valve shell, inner parts and sealing surface material, in addition to considering the physical properties of the working medium (temperature, pressure) and chemical properties (corrosion), should also master the degree of media cleanliness (with or without solid particles), in addition, but also refer to the relevant provisions of the state and the use of departments.
Correct and reasonable choice of valve material can obtain the best economic service life and better performance of the valve. Valve body material selection order: cast iron – carbon steel – stainless steel, sealing ring material selection order: rubber – copper – alloy steel -F4.
Five other
In ADDITION, THE FLOW RATE AND PRESSURE LEVEL OF THE FLUID FLOWING THROUGH the VALVE SHOULD BE determined, AND THE appropriate valve should be selected using the available information (e.g., valve product catalog, valve product sample, etc.).
Description of common valve type selection
Specification of gate valve type selection
In general, priority should be given to gate valves. Gate valve in addition to suitable for steam, oil and other media, but also applicable to contain granular solid and viscosity of the medium, and is suitable for vent and low vacuum system valves. For medium with solid particles, the gate valve body shall be provided with one or two purge holes. For low temperature medium, low temperature gate valve should be selected.
2. Description of cut-off valve selection
Globe valve is suitable for fluid resistance requirements are not strict on the pipeline, that is, the pressure loss is not considered, and high temperature, high pressure medium pipeline or device, suitable for DN < 200mm steam and other media pipeline;
Small valve can choose the globe valve, such as needle valve, instrument valve, sampling valve, pressure gauge valve, etc.;
The globe valve has flow regulation or pressure regulation, but the adjustment accuracy is not high, and the pipe diameter is relatively small, it is appropriate to choose the globe valve or throttle valve;
For highly toxic medium, it is appropriate to choose bellows sealed globe valve; But the globe valve should not be used for medium with large viscosity and medium containing particles easy to precipitate, and should not be used as a vent valve and the valve of low vacuum system.
3. Specification of ball valve selection
Ball valve is suitable for low temperature, high pressure, viscosity medium. Most ball valves can be used in medium with suspended solid particles, according to the sealing material requirements can also be used in powder and granular media;
The all-channel ball valve is not suitable for flow regulation, but is suitable for quick opening and closing occasions, easy to achieve emergency cut off; Usually in strict sealing performance, wear, shrinkage channel, rapid opening and closing action, high pressure cutoff (large pressure difference), low noise, gasification phenomenon, small operating torque, fluid resistance, the use of ball valves is recommended.
Ball valve is suitable for light structure, low pressure cut-off, corrosive media; Ball valve or low temperature, cryogenic medium of the ideal valve, low temperature medium piping system and device, should be selected with a low temperature ball valve cover;
The floating ball ball valve seat material should undertake the load of the ball and the working medium, large caliber ball valve in operation requires greater force, DN≥
200mm ball valve should choose worm gear transmission form; Fixed ball valve is suitable for larger diameter and high pressure occasions; In addition, the ball valve used for the process of highly toxic materials, combustible media pipeline, should have fire, anti-static structure.
4. Description of throttle valve selection
Throttle valve is suitable for low temperature medium, high pressure occasions, suitable for the need to adjust the flow and pressure parts, not for viscosity and containing solid particles medium, should not be used as a block valve.
Description of plug valve type selection
Plug valve is suitable for rapid opening and closing occasions, generally not suitable for steam and high temperature medium, for low temperature, high viscosity medium, also suitable for medium with suspended particles.
Description of butterfly valve type selection
Butterfly valve is suitable for large diameter (such as DN>600mm) and short structure length requirements, and the need for flow regulation and rapid opening and closing requirements, generally used for temperature ≤
80℃, pressure ≤1.0MPa water, oil and compressed air and other media; Due to the butterfly valve relative to gate valve, ball valve pressure loss is relatively large, so butterfly valve is suitable for the pressure loss requirements are not strict in the pipeline system.
Description of check valve selection
Check valve is generally suitable for clean media, should not be used in the medium containing solid particles and large viscosity. When ≤40mm, it is advisable to use lift check valve (* allowed to be installed on the horizontal pipeline); When DN = 50 ~ 400mm, it is appropriate to use swing type lift check valve (in the horizontal and vertical pipeline can be installed, such as installed in the vertical pipeline, medium flow from the bottom up);
When DN≥450mm, buffer type check valve should be used; When DN = 100 ~ 400mm can also choose the clamp type check valve; Swing check valve can be made of very high working pressure, PN can reach 42MPa, according to the shell and seal material can be applied to any working medium and any working temperature range.
The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196 ℃ and 800℃.
Description of diaphragm valve selection
Diaphragm valve is suitable for working temperature less than 200℃, pressure less than 1.0MPa oil, water, acid medium and medium containing suspended matter, not suitable for organic solvents and strong oxidant medium;
Abrasive granular medium should choose weir diaphragm valve, choose weir diaphragm valve to refer to its flow characteristics table; Viscous fluid, cement slurry and precipitating medium should be selected straight through diaphragm valve; Unless otherwise specified, the diaphragm valve should not be used on vacuum lines and vacuum equipment.