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In the fluid piping system, the valve is a control element, its main function is to isolate the equipment and piping system, regulate the flow rate, prevent backflow, adjust and discharge the pressure.Because it is very important to choose the most suitable valve ,so it is very important to understand the characteristics of the valve and the steps and basis of selecting the valve.
1. Valve characteristics
Use characteristics: it determines the main service performance and service scope of the valve. Valve categories (closed valve, regulating valve, safety valve, etc.);
Valve types: (gate valve, globe valve, butterfly valve, ball valve, etc.); material of main valve parts (valve body, valve cap, valve stem, valve flap, sealing surface); valve drive mode, etc.
Structural characteristics: it determines the valve’s installation, repair and maintenance etc.,Structural length and overall height of the valve, and the connection form of the pipeline (flange connection, thread connection, clamp connection, external thread connection, welding end connection, etc.) are structural characters;
The form of sealing surface: (ring, thread ring, pile welding, spray welding, valve body ); structural form of valve stem (rotating stem, rising and nonrising stem), etc.
2. Valve selection steps
① defines the use of the valve in the equipment or device, and determines the working conditions of the valve: applicable medium, working pressure, working temperature, etc.
② determines the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.
③ determines the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electric-hydraulic linkage, etc.
④ determines the materials of the shell and interior of according to the transmission medium, working pressure and working temperature. Grey cast iron, malleable iron, ductile iron, carbon steel, alloy steel, stainless acid resistant steel, copper alloy, etc.
⑤ Select the types of valves: closed valve, regulating valve, safety valve, etc.
⑥ determines the type of the valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure relief valve, steam drain valve, etc.
⑦ determines the parameters of the valve: for automatic valves, first determine the allowable flow resistance, discharge capacity, back pressure, and then determine the nominal diameter of the pipe and the diameter of the seat hole.
⑧ determines the geometric parameters of the valve: structure length,connection form and size of flange, size of valve height direction after opening and closing, size and quantity of bolt holes connected, external size of the whole valve, etc.
⑨ uses available data: valve catalogue,valve technical information table, etc.
3. Valve selection basis
①The application, operating conditions and control mode of valves.
②working medium: working pressure, working temperature, corrosive performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable and explosive medium, medium viscosity and so on.
③ requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
④ installation dimensions and shape dimension requirements: nominal access diameter, connection mode and connection size with pipes, shape size or weight limit, etc.
⑤ Additional requirements for valve product reliability, service life and explosion-proof performance of electric devices.
According to the above basis and steps of valve selection, the reasonable and correct selection of the valve must also understand the internal structure of various types of valves in detail, so as to make the correct choice of the preferred valve.
The final control of the pipe is the valve.The valve opening and closing parts control the flow beam mode of the medium in the pipeline. The shape of the valve flow channel gives the valve certain flow characteristics, which must be taken into account when selecting the most suitable valve for the pipeline system.
4. The principle to be followed in the valve selection
Valves for closing and open media
The valves which flow channel is a direct type, its flow resistance is small, usually selected as a cut-off and open medium valve.Down closed valve (globe valve, plunger valve) because of its flow channel twists and turns, flow resistance is higher than other valves, so less selected.Unless high flow resistance is allowed.
Valves for flow control
Valves that are easy to regulate the flow rate are usually selected for flow control.Down closed valve (e. g. globe valve) is suitable for this purpose because its seat size is proportional to the stroke of the closing parts.Rotary valves (plug, butterfly, ball valves) and flexible body valves (clamp valves, diaphragm valves) can also be used for throttle control, but usually only within a limited valve diameter range.Gate valve is a disc switch plate of the circular valve seat to do cross cutting movement, it is only close to the closing position, can better control the flow, so it is usually not used for flow control.
Valves for diversion diversion
The valve may have three or more channels.Plug valves and ball valves are more suitable for this purpose, so most valves used for diversion are selected from one of these valves.But in some cases, other types of valves can also be used for diversion, if two or more valves are properly connected to each other.
Valves for medium with suspended particles
When the medium contains suspended particles,it is better to choose the valves which closing parts sliding along the sealing face with wiping action. If the closing part moving vertical to the valve seat, the particles may be clamped, so the valve is only suitable for clean media unless the sealing surface material can allow the embedding of the particles.Ball valve and plug valve can wipe the sealing surface during the opening and closing process, so it is suitable for use in the medium with suspended particles.
We can supply valves for water: ball valve, gate valve, globe valve, check valve ,butterfly valve,strainer etc.,
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