Selection of valves is based on the operational and safety and economic rationality, the overall balance of comparative experience results.
The following original conditions must be presented before the valve is selected:
1. Physical property
(1) Material status A．
The material status of the gas material includes: the physical data, the pure gas or the mixture, whether there are droplets or solid particles, whether there is an easily condensed component. b．
The material status of the liquid material includes:
(1) related to physical data, whether the pure composition or mixture contains volatile parts or dissolved gas (the pressure can precipitate the formation of two-phase flow), whether the suspension of solids, as well as the viscosity of liquids, freezing point or pour point. (2) Other properties, including corrosive, toxicity, to the valve structural material solubility, whether flammable and explosive performance.
These properties sometimes not only affect the material, but also cause special structural requirements, or the need to improve the pipeline level.
2. Working conditions under operating condition
(1) In accordance with the normal operating conditions of temperature and pressure, but also need to combine the work of a shutdown or regeneration of working conditions. A．
Pump outlet valve should consider the maximum pressure of the pump shutdown. b．
When the regeneration temperature of the system is higher than the normal temperature, but the pressure is reduced, for this type of system, we should consider the effect of temperature and pressure synthesis. C．
Operating continuity: That is, valve opening and closing frequency, but also affect the wear-resistant requirements, switching more frequent system, should consider whether to install dual valves.
(2) System allowable pressure drop A．
System allows the pressure drop is small, or allow pressure to drop a small but do not need to adjust the flow, you should choose a small pressure drop valve type such as gate valve, straight through the ball valve. b．
Need to adjust the flow, you should choose to adjust the performance of a good, with a certain pressure drop valve type (pressure drop accounted for the entire pipeline pressure drop ratio and the sensitivity of the adjustment).
(3) Valve environment: In the cold area of the outdoor, especially for chemical materials, valve body material is generally not available cast iron and should choose cast steel (or stainless steel).
3. Valve function (1) Cut off: Almost all valves have cut off function. Simply used to cut off without the need to adjust the flow can choose gate valve, ball valve, etc., requiring rapid cutting, then to plug, ball valve, butterfly valve, etc. more appropriate. The cut-off valve can both adjust the flow and cut off.
Butterfly valve can also be suitable for large flow adjustment.
(2) Change the direction of flow: Choose two (channel for L-shaped) or tee (channel is T-shaped) ball valve or plug, can quickly change the flow of materials, and because a valve up to more than two straight valve function, can simplify the operation, make the switch accurate, and can reduce the space occupied.
(3) Regulation: cut-off valve, plunger valve can meet the general flow adjustment, needle valve can be used for micro-adjustment, in a large flow range of stability (pressure, flow) of the regulation, the throttle valve is advisable.
(4) Check: Check valve should be used to prevent material from flowing back.
(5) Different production process can choose to have additional function of the valve, such as with jacket, with row Kangkou and with bypass valve, there is used to prevent the deposition of solid particles with the valve, such as blowing.
4, Switch valve power In-situ operation of the vast majority of the valve with handwheel, the operation with a certain distance, can be used sprocket or lengthened rod. Some large-caliber valves are already equipped with motors when the valve is designed because of the large starting torque. In the explosion-proof zone to use the corresponding level of explosion-proof motor. Remote CONTROL valve: The type of power to adopt pneumatic, hydraulic, electric and so on, which can be divided into solenoid valve and motor-driven valve. Should be based on the needs and the energy available to choose.