Valve selection strategy! Collection! Valve type and drive type selection reference

Valve selection strategy! Collection! Valve type and drive type selection reference

In fluid piping systems, valves are control elements whose main role is to isolate equipment and piping systems, regulate flow, prevent backflow, regulate and discharge pressure. It can be used to control the flow of air, water, steam, all kinds of corrosive media, mud, oil, liquid metal and radioactive media. Because the piping system to choose the most suitable valve is very important, so, to understand the characteristics of the valve and the selection of the valve steps and basis also become crucial.
In fluid piping systems, valves are control elements whose main role is to isolate equipment and piping systems, regulate flow, prevent backflow, regulate and discharge pressure. It can be used to control the flow of air, water, steam, all kinds of corrosive media, mud, oil, liquid metal and radioactive media. Because the piping system to choose the most suitable valve is very important, so, to understand the characteristics of the valve and the selection of the valve steps and basis also become crucial.
Classification of valves
First, the valve can be divided into two categories:
Class automatic valve: depends on the medium (liquid, gas) its own ability to operate the valve.
Such as check valve, safety valve, regulating valve, trap, pressure reducing valve, etc.
The second type of drive valve: with the help of manual, electric, hydraulic, pneumatic to control the action of the valve.
Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, plug valve and so on.
Two, according to the structural characteristics, according to the direction of the closing part relative to the valve seat movement can be divided:
1. Stop door shape: the closing part moves along the center of the seat;
2. Gate shape: the closing piece moves along the vertical center of the seat;
3. Cock and ball: the closing piece is the plunger or ball, revolving around its center line;
4. Swing shape: the closing part rotates around the shaft outside the seat;
5. Disc: the disc of the closing part rotates around the shaft in the seat;
6. Slide valve shape: the closing piece slides in the direction perpendicular to the channel.
Three, according to the use, according to the different uses of the valve can be divided:
1. Breaking: used to connect or cut off pipeline media, such as globe valve, gate valve, ball valve, butterfly valve, etc.
2. Check: used to prevent media backflow, such as check valve.
3 adjustment with: used to adjust the pressure and flow of the medium, such as regulating valve, pressure reducing valve.
4. Distribution: used to change the flow direction of the medium, distribution medium, such as three-way cock, distribution valve, slide valve, etc.
5. Safety valve: when the medium pressure exceeds the specified value, it is used to discharge excess medium to ensure the safety of piping system and equipment, such as safety valve and accident valve.
6. Other special uses: such as trap, vent valve, drain valve, etc.
Four, according to the driving mode, according to different driving mode can be divided:
1. Manual: with the help of hand wheel, handle, lever or sprocket, there is human drive, transmission torque is equipped with worm gear, gear and other reduction devices.
2. Electric: driven by motor or other electrical devices.
3. Hydraulic: driven by (water, oil).
4. Pneumatic: driven by compressed air.
Five, according to the pressure, according to the nominal pressure of the valve can be divided:
1. Vacuum valve: *** pressure 0.1Mpa, namely 760mm mercury high valve, usually with mm mercury or mm water column to represent the pressure.
2. Low pressure valve: nominal pressure PN≤1.6Mpa valve (including PN≤1.6MPa steel valve)
3. Medium pressure valve: nominal pressure PN2.5-6.4mpa valve.
4 high pressure valve: nominal pressure PN10.0-80.0MPa valve.
5. Ultra high pressure valve: nominal pressure PN≥100.0MPa valve.
Six, according to the temperature of the medium, according to the valve working medium temperature can be divided:
1. Common valve: suitable for medium temperature -40℃ ~ 425℃ valve.
2. High temperature valve: suitable for the medium temperature of 425℃ ~ 600℃ valve.
3. Heat resistant valve: suitable for the medium temperature of 600℃ or above the valve.
4. Low temperature valve: suitable for medium temperature -150℃ ~ -40℃ valve.
5.** temperature valve: suitable for the medium temperature below -150℃ valve.
Seven, according to the nominal diameter, according to the nominal diameter of the valve can be divided:
1. Small diameter valve: nominal diameter DN40mm valve.
2. Medium diameter valve: nominal diameter DN50 ~ 300mm valve.
3. Large diameter valve: nominal diameter DN350 ~ 1200mm valve.
4. Extra-large diameter valve: nominal diameter DN≥1400mm valve.
Eight, according to the connection mode and pipeline, according to the valve and pipeline connection mode can be divided:
1. Flanged valve: the valve body is equipped with a flange, and the pipe is connected with a flange valve.
2. Threaded valve: the valve body with internal or external thread, and the pipe with thread connection valve.
3. Weld the valve: the valve body is equipped with a welding mouth, and the valve is welded to the pipe.
4 clamp valve connection: the valve body with a clamp, and the pipe is connected with a clamp valve.
5. Sleeve connection valve: the valve is connected with the pipe by the sleeve.
Characteristics of valves
Valve characteristics are generally of two kinds, service characteristics and structural characteristics.
Use characteristics: it determines the main use of the valve performance and range of use, belong to the valve use characteristics are: valve category (closed circuit valve, regulating valve, safety valve, etc.); Product type (gate valve, globe valve, butterfly valve, ball valve, etc.); The main parts of the valve (valve body, cover, stem, disc, sealing surface) material; Valve transmission mode, etc.
Structural characteristics: it determines the installation of the valve, repair, maintenance and other methods of some structural characteristics, belonging to the structural characteristics are: the structural length of the valve and the overall height, and the pipe connection form (flange connection, thread connection, hoop connection, external thread connection, welding end connection, etc.); The form of sealing surface (insert ring, thread ring, surfacing, spray welding, body body); Valve stem structure form (rotating rod, lifting rod), etc.
Valve selection procedures and basis
Selection steps:
1, clear valve in equipment or device use, determine the working conditions of the valve: applicable medium, working pressure, working temperature and so on.
2, determine the nominal diameter and connection method of the pipe connecting with the valve: flange, thread, welding, etc.
3, determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.
4, according to the pipeline transmission medium, working pressure, working temperature to determine the selected valve shell and inner parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
5, choose 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 allowed flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.
8, determine the selected geometric parameters of the valve: structure length, flange connection form and size, open and close the valve height direction of size, the connection of the bolt hole size and number, the size of the entire valve shape.
9, the use of existing information: valve product catalog, valve product samples and other appropriate valve products.
Selection of valve basis:
In the understanding of the selection of valve steps, but also should further understand the basis for the selection of valves.
1, the use of the selected valve, operating conditions and control mode.
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, the valve fluid characteristics of the requirements: flow resistance, discharge capacity, flow characteristics, sealing grade and so on.
4, installation size and external size requirements: nominal diameter, connection with the pipe and connection size, external size or weight limit.
5. Additional requirements on the reliability, service life and explosion-proof performance of the valve products.
When selecting parameters, note that:
If the VALVE IS to BE USED FOR control PURPOSES, THE following additional parameters MUST BE DETERMINED: method of operation, maximum AND minimum flow requirements, pressure drop for normal flow, pressure drop at closing, maximum AND minimum inlet pressure for the valve.
According to the above selection of valve basis and steps, reasonable and correct selection of the valve must also be a detailed understanding of the internal structure of various types of valves, in order to be able to preferentially choose the valve to make a correct choice.
The ultimate control of the pipeline is the valve. Valve opening and closing parts control the flow of media in the pipeline, the shape of the valve flow channel enables the valve to have a certain flow characteristics, which must be taken into account when selecting the valve suitable for installation in the pipeline system.
Select the valve should follow the principle
1, cut-off and open medium with the valve
The flow channel is a straight-through valve, the flow resistance is small, usually selected as a cut-off and open medium with the valve. Downward closed valve (globe valve, plunger valve) because of its tortuous flow path, flow resistance is higher than other valves, so less selected. Closed valves may be used where high flow resistance is permitted.
2, control the flow of valves
A valve that is easy to adjust is usually chosen to control flow. Downward CLOSING valves (such AS GLOBE valves) ARE SUITABLE FOR THIS PURPOSE BECAUSE THE SEAT size IS PROPORTIONAL TO THE STROKE OF THE SHUTOFF. Rotary VALVES (PLUG, butterfly, BALL valves) and FLEXURE BODY VALVES (PINCH, DIAPHRAGM) ARE ALSO AVAILABLE FOR THROTTLING CONTROL, but USUALLY ONLY IN a limited range of valve DIAMETERS. Gate VALVE IS A disc shaped gate to the circular seat port to do transverse motion, it only in close to the closed position, can better control the flow, so usually not used for flow control.
3. Valve for reversing and diverting
The valve may have three or more channels, depending on the need for reversing and diverting. Plug and ball valves are more suitable for this purpose, and therefore, most valves used for reversing and diverting are selected as one of these valves. However, IN SOME CASES, other TYPES OF VALVES MAY ALSO BE USED AS commutATION diverTERS, PROVIDED THAT TWO or MORE VALVES ARE properly connected to EACH other.
4. Valves for medium with suspended particles
When the medium with suspended particles, ** suitable for the use of the closing parts along the sealing surface of the sliding valve with wiping action. If THE SHUTOFF IS VERTICAL TO THE BACK AND FORTH MOVEMENT OF THE SEAT, PARTICLES MAY BE TRAPPED, SO THIS VALVE IS ONLY SUITABLE FOR BASICALLY CLEAN MEDIA UNLESS THE SEALING MATERIAL ALLOWS FOR PARTICLES TO BE EMBEDDED. Ball valves and plug valves wipe the sealing surface during opening and closing, so they are suitable for use in media with suspended particles.