Select the valve is based on operational and safety and economic rationality, the balance of comparative experience. The following preconditions must be proposed before choosing a valve:
1, physical properties
(1) material status
a. The material status of the gas material includes: physical property data, pure gas or mixture, whether there are droplets or solid particles, whether there is easy to condense the ingredients.
b. The material status of the liquid material includes:
(1) whether physical data, pure components or mixtures contain volatile components or dissolved gas (which can form two-phase flow when pressure is reduced), whether or not it contains solid suspended solids, and the consistency of the liquid, the freezing point or the pour point Point and so on.
(2) other properties; including corrosive, toxic, structural properties of the valve solubility, whether flammable and explosive performance. These properties sometimes affect not only the material but also the structural special requirements or the need to increase the pipe grade.
2, the operating conditions of the working conditions
(1) According to the temperature and pressure under normal working conditions, it is also necessary to combine with the working conditions during shutdown or regeneration.
a. Pump outlet valve should consider the maximum closing pressure of the pump.
b. When the system regeneration temperature is much higher than normal, but the pressure is reduced, for this type of system, consider the combined effect of temperature and pressure.
c. The degree of continuity of operation: that is, the frequency of valve opening and closing, but also affect the degree of wear resistance requirements, switch more frequently in the system, should consider whether to install dual valve.
(2) The system allows the pressure drop
a. The system allows the pressure drop is small, or allows the pressure drop is not small but does not require flow adjustment, you should use the pressure drop smaller valve type, such as gate valve, through the ball valve.
b. Need to adjust the flow, you should choose to adjust the performance better, with a certain pressure drop valve (pressure drop accounting for the entire pipeline pressure drop proportional to the sensitivity and regulation).
(3) the valve environment: In the cold area of the outdoor, especially for chemical materials, body material generally not available cast iron and should use cast steel (or stainless steel).
3, valve function
(1) cut off: almost all of the valves have cut off function. Purely used for cutting without regulating the flow of the valve can be used, such as ball valve, when asked to cut off quickly, then the cock, ball valve, butterfly valve and more appropriate. Globe valve can adjust the flow can be cut off. Butterfly valve can also be suitable for large flow regulation.
(2) to change the flow: the choice of two-way (channel L-shaped) or tee (channel T-shaped) ball valve or tap, you can quickly change the material flow, and as a valve play more than two through-valve action, can be simplified Operation, so that the switch is accurate, and can reduce the share of space.
(3) regulation: globe valve, plunger valve to meet the general flow adjustment, needle valve can be used for trace fine adjustment; in a large flow range for stability (pressure, flow) regulation, the throttle is appropriate .
(4) Check: Need to prevent the back flow of material can be used check valve.
(5) different production process can choose to have additional features of the valve, if there is a jacket, with a clean mouth and bypass valve, there are used to prevent the settlement of solid particles with a blow valve.
4, the power switch valve
Local operation of the vast majority of the valve with the hand wheel, with the operation with a certain distance, the sprocket or extension can be used. Some large-caliber valves due to the starting torque is too large in the design of the valve with a motor. Explosion-proof area to use the appropriate level of explosion-proof motor. Remote control valve: Take the power of the types of pneumatic, hydraulic, electric, etc., which can be divided into electric and solenoid valve driven by the motor. Should be based on needs and can provide the energy to choose.
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