In fluid piping systems, valves are control elements whose main roles are to isolate equipment and piping systems, regulate flow, prevent backflow, and regulate and discharge pressure. Since it is very important to choose the most suitable valve for the piping system, it becomes vital to understand the characteristics of the valve and the steps and basis for valve selection.
Valve industry so far, has been able to produce a full range of gate valves, globe valves, throttle valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, steam traps and emergency shut-off valves and other 12 categories, more than 3,000 models, more than 4,000 specifications of valve products; the highest working pressure of 600MPa, the maximum nominal diameter of 5350mm, the highest Working temperature of 1200 ℃, the minimum working temperature of -196 ℃, the applicable media for water, steam, oil, natural gas, strong corrosive media (such as concentrated nitric acid, medium concentration of sulfuric acid, etc.), flammable media (such as stupid, ethylene, etc.), toxic media (such as hydrogen sulfide), explosive media and with radioactive media (sodium metal, - circuit pure water, etc.). Valve bearing material cast copper, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless acid-resistant steel, Hastelloy, Inconel, Monel alloy, duplex stainless steel, titanium alloy, etc.. And we can produce all kinds of electric, pneumatic and hydraulic valve actuators. In the face of so many varieties of valves and such a variety of complex working conditions, to choose the most suitable for the installation of pipeline systems valve products, I think, first of all, should understand the characteristics of the valve; secondly, should master the steps and basis for selecting the valve; and then should follow the principles of selecting the valve.
1. The characteristics of the valve generally have two kinds, the use of characteristics and structural characteristics.
Use characteristics: It determines the valve's main performance and use of the scope of the valve characteristics are: the type of valve (closed-circuit valves, regulating valves, safety valves, etc.); product type (gate valves, globe valves, butterfly valves, ball valves, etc.); valve main parts (valve body, bonnet, stem, valve flap, sealing surface) materials; valve transmission mode.
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Structural characteristics: it determines the valve installation, repair, maintenance and other methods of some structural characteristics, belonging to the structural characteristics are: the structure of the valve length and overall height, the form of connection with the pipeline (flange connection, threaded connection, clamped connection, external threaded connection, welded end connection, etc.); the form of sealing surface (inlay ring, threaded ring, weld, spray welding, valve body); stem structure form (rotary rod, lift (lever), etc. 2.
2. The steps and basis for selecting the valve are generally as follows.
(1) selection steps
① clarify the use of the valve in the equipment or device, to determine the working conditions of the valve: applicable media, working pressure, working temperature, etc.
② Determine the nominal diameter of the pipe connected to the valve and the connection: flange, thread, welding, etc.
③ Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.
④ Determine the material of the shell and inner parts of the selected valve according to the medium, working pressure and working temperature of the pipeline: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
⑤ Select the type of valve: closed circuit valve, regulating valve, safety valve, etc.
⑥ Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.
(7) Determine the parameters of the valve: for automatic valves, according to different needs to determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the seat hole.
⑧ determine the geometric parameters of the selected valve: the length of the structure, flange connection form and size, the size of the valve height direction after opening and closing, the size and number of connected bolt holes, the entire valve external dimensions, etc.
⑨ Use the available information: valve catalogs, valve product samples, etc. to select the appropriate valve products.