Functions Of Valves And Factors To Consider When Selecting Them
The selection of Ball Valve is the result of comprehensive and balanced comparison based on the rationality of operation, safety and economy. The following initial conditions must be put forward before selecting a valve:
1. Physical properties
(1) Material state
a. The material state of gas materials includes: relevant physical property data, pure gas or mixture, whether there are droplets or solid particles, and whether there are easily condensed components.
b. The material state of liquid materials includes:
(1) Relevant physical property data, whether the pure component or mixture contains volatile components or dissolved gases (which can precipitate to form a two-phase flow when the pressure is reduced), whether it contains solid suspended matter, and the viscosity, freezing point or pour point of the liquid.
(2) Other properties; including corrosiveness, toxicity, solubility in valve structural materials, whether it is flammable and explosive, etc. These properties sometimes not only affect the material, but also cause special structural requirements, or require an increase in the pipeline grade.
2. Working conditions under operating conditions
(1) According to the temperature and pressure under normal working conditions, it is also necessary to combine the working conditions during start-up, shutdown or regeneration.
a. The pump outlet valve should consider the maximum closing pressure of the pump.
b. When the system regeneration temperature is much higher than the normal temperature, but the pressure is reduced, for this type of system, the combined effects of temperature and pressure should be considered.
c. The degree of continuity of operation: that is, the frequency of valve opening and closing, also affects the requirements for wear resistance. For systems with frequent opening and closing, it is necessary to consider whether to install double valves.
(2) Allowable pressure drop of the system
a. When the system allows a small pressure drop, or allows a large pressure drop but does not require flow regulation, a valve type with a small pressure drop should be selected, such as a gate valve, a straight-through ball valve, etc.
b. If flow regulation is required, a valve type with good regulation performance and a certain pressure drop should be selected (the proportion of pressure drop to the entire pipeline pressure drop is related to the sensitivity of regulation).
(3) The environment in which the valve is located: Outdoor in cold areas, especially for chemical materials, the valve body material is generally not cast iron but cast steel (or stainless steel) should be selected.
3. Valve function
(1) Cut-off: Almost all valves have a cut-off function. If it is only used for cutting off without adjusting the flow, gate valves, ball valves, etc. can be selected. If it is required to cut off quickly, plug valves, ball valves, butterfly valves, etc. are more suitable. Stop valves can both adjust the flow and cut off. Butterfly valves are also suitable for adjusting large flows.
(2) Changing flow direction: Selecting a two-way (L-shaped channel) or three-way (T-shaped channel) ball valve or plug valve can quickly change the flow direction of materials. Since one valve plays the role of more than two straight-through valves, it can simplify the operation, make the switching accurate, and reduce the space occupied.
(3) Regulation: Stop valves and plunger valves can meet general flow regulation, and needle valves can be used for micro-fine adjustments; for stable (pressure, flow) regulation in a larger flow range, throttle valves are more suitable.
(4) Check: Check valves can be used to prevent material backflow.
(5) Different production processes can choose valves with additional functions, such as valves with jackets, drain ports and bypasses, and valves with air ports to prevent the sedimentation of solid particles.
4. Power of valve switch
Most valves operated on site use hand wheels. For valves that are a certain distance from the operating belt, sprockets or extension rods can be used. Some large-diameter valves are designed with motors due to excessive starting torque. Explosion-proof motors of corresponding grades should be used in explosion-proof areas. Remote control valves: The power types adopted include pneumatic, hydraulic, electric, etc. Among them, electric can be divided into solenoid valves and motor-driven valves. It should be selected according to needs and the energy available.
