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How to choose the right valve in the pipeline design?

发布日期：2019-07-27 23:55:00 点击数：3930 次新闻来源：

In fluid piping systems, valves are control elements whose primary function is to isolate equipment and piping, regulate flow, prevent backflow, regulate and drain 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 steps and basis for selecting the valve.
First, the characteristics of the valve
Use characteristics: It determines the main performance and scope of use of the valve. It belongs to the valve characteristics: valve category (closed valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.) The material of the main parts of the valve (valve body, valve cover, valve stem, valve disc, sealing surface); valve transmission mode.
Structural characteristics: It determines some structural characteristics of the valve installation, repair, maintenance and other methods. The structural characteristics are: the structural length and overall height of the valve, and the connection form with the pipe (flange connection, thread connection, clamp connection) , external thread connection, welding end connection, etc.; the form of the sealing surface (insert ring, thread ring, surfacing, spray welding, valve body); valve stem structure (rotating rod, lifting rod).
Second, the valve selection steps
1 Defining the purpose of the valve in the equipment or device, 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 connected to 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 medium, working pressure and working temperature of the pipeline, determine the materials of the casing and internal parts of the selected valve: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
5Select 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, and so on.
7 Determine the parameters of the valve: For automatic valves, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipe and the diameter of the seat hole.
8 Determine the geometric parameters of the selected valve: structural length, flange connection form and size, dimensions of the valve height direction after opening and closing, bolt hole size and number of connections, and overall valve dimensions.
9 Use the existing information: valve catalogue, valve product samples, etc. to select the appropriate valve products.
Third, the valve selection basis
1 The purpose of the selected valve, the working conditions and the control method.
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, viscosity of the medium, etc.
3 requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing level, etc.
4 Installation size and dimensions: nominal diameter, connection to the pipe and connection size, dimensions or weight restrictions.
5 additional requirements for the reliability, service life and explosion-proof performance of the valve.
According to the above-mentioned basis and steps of selecting the valve, the internal structure of each type of valve must be well understood in order to properly and correctly select the valve, so that the correct choice can be made for the preferred valve.
The final control of the pipe is the valve. The valve opening and closing member controls the flow pattern of the medium in the pipe. The shape of the valve flow path allows the valve to have a certain flow characteristic, which must be taken into account when selecting the most suitable valve for the pipe system.
Fourth, the principle of selecting valves should follow
Valves for cut-off and open media
The flow path is a straight-through valve with a small flow resistance and is usually selected as a valve for cut-off and open media. Down-closed valves (shut-off valves, plunger valves) are less preferred because of their tortuous path and higher flow resistance than other valves. Where a higher flow resistance is allowed, a closed valve can be used.
Valve for controlling flow
A valve that is easy to adjust the flow rate is usually selected as the control flow. A down-closed valve (such as a shut-off valve) is suitable for this purpose because its seat size is proportional to the stroke of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexing valve body valves (clamping valves, diaphragm valves) can also be used for throttling control, but are usually only available in a limited range of valve sizes. The gate valve is a cross-cut movement of the circular valve seat with a disc-shaped shutter. It can control the flow better only when it is close to the closed position, so it is usually not used for flow control.
Reversing split valve
This valve can have three or more passages depending on the need for a commutation split. Plug valves and ball valves are more suitable for this purpose, so most of the valves used for commutating splits select one of these types of valves. However, in some cases, other types of valves may be used for commutation splitting by simply interconnecting two or more valves.
Valve for medium with suspended particles
When the medium has suspended particles, it is most suitable to use a valve with a wiping action of the sliding member along the sealing surface. If the closing movement of the closure to the valve seat is vertical, it is possible to hold the particles, so that the valve is only suitable for substantially clean media unless the sealing surface material allows for the incorporation of particles. The ball valve and the plug valve have a wiping action on the sealing surface during the opening and closing process, so it is suitable for use in a medium with suspended particles.
At present, in the petroleum, chemical, and other industries, the valve application, operating frequency and service are ever-changing. To control or eliminate even the slightest leakage, the most important and critical equipment is the valve. The ultimate control of the pipe is the valve, and the service and reliable performance of the valve in all areas is unique.

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