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In fluid piping systems, the valve is the control element, its main role is to isolate equipment and piping systems, regulate flow, prevent backflow, regulate and discharge pressure. Since it is important to select the most suitable valve for the piping system, it is important to understand the characteristics of the valve and the procedure and basis for selecting the valve.
1.Characteristics Of Valves
Use Characteristics: It determines the main performance and use of the valve, the use of the characteristics of the valve are: Valve Types (closed-circuit Valves, control valves, safety valves, etc.) ; Product Types (gate valves, globe valves, butterfly valves, ball valves, etc.) ; Valve Main Parts Material (body, cover, stem, disc, sealing surface) ; valve drive mode
Structural characteristics: It determines some of the structural characteristics of valve installation, repair, maintenance, etc. , structural characteristics include: The structural length and overall height of the valve, and pipe connection form (flange connection, thread connection, clamp connection, external thread connection, welding end connection, etc.) ; Sealing surface form (insert ring, thread ring, build-up welding, spray welding, valve body) ; Valve stem structure form (rotating rod, lifting rod) and so on.
2.Valve Selection Procedure
1) Specify the use of the valve in the equipment or device and determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc. .
2) Determine the nominal diameter and connection mode of the pipe to the valve: Flange, thread, welding, etc. .
3) Determine how to operate the valve: manually, electrically, electromagnetically, pneumatically or hydraulically, electrically or electrohydraulically.
4) According to the medium of pipeline transportation, working pressure and working temperature, the materials of the shell and inner parts of the selected valve are determined: 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
6) Determine the type of valve
7) Determine valve parameters: for automatic valves, according to different needs, first determine the allowable flow resistance, discharge capacity, back pressure, and then determine the nominal diameter of the pipeline and valve seat hole diameter.
8) Determine the selected valve geometric parameters: structural length, flange connection type and size, after opening and closing the size of the valve height direction, connecting the size and number of bolt hole, the overall valve shape size. Use The available information: valve product catalog, valve product sample, etc. to select the appropriate valve product.
3. Valve selection basis
1) The use, operating condition and control mode of the valve selected.
2) The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, medium viscosity and so on.
3) Requirements For Valve Fluid Characteristics: flow resistance, discharge capacity, flow characteristics, seal rating, etc. .
4) Installation size and outline size requirements: nominal size, connection with pipe and connection size, outline size or weight limit, etc. .
5) Additional requirements for reliability, service life of valve products and explosion-proof performance of electric installations.