In fluid piping system, valves are control elements, whose main functions are isolating equipment and piping system, regulating flow rate, preventing backflow, regulating and discharging pressure. Because the most suitable valve for piping system is very important, it is very important to understand the characteristics of valve and choose the steps and basis of valve.

The valve industry, so far, has been able to produce the full range of gate valve, globe valve, throttle valve, plug valve, ball valve, electric valve, diaphragm valve, check valve, safety valve, pressure reducing valve, steam trap and emergency shut-off valve in 12 categories, more than 3000 types, more than 4000 specifications of valve products; the maximum working pressure is 600MPa, the maximum nominal diameter 5350mm, the maximum working temperature of 1200 DEG C, the lowest working temperature of -196, it is used to water, steam, oil, natural gas, corrosive media (such as concentrated nitric acid, concentration of sulfuric acid), inflammable medium (such as benzene, ethylene, etc.) toxic materials (such as hydrogen sulfide), and radioactive and explosive medium, medium (sodium metal, water loop etc.). Pieces of material bearing bronze valve, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, low-alloy steel, stainless steel, Hastelloy, Inconel Seoul, Monel alloy, duplex stainless steel, titanium alloy. And can produce all kinds of electric, pneumatic, hydraulic valve driving device. The valve face of so many varieties and complexity of various conditions, to choose the most suitable for installation of piping system valve product, I think, should first understand the characteristics of the valve; second should master the steps and the basis for selection of the valve; the valve should follow the principle of choice.

1. characteristics of valves are generally two, using characteristics and structural characteristics.

The use of characteristics: it determines the main valve and the use of performance, is using the characteristics of the valve are: valve type (closed valves, regulating valves, safety valves etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.); the main parts of the valve (valve body, valve cover, valve stem, valve the material, sealing surface); valve drive pattern.

Structural characteristics: it determines the structure characteristics of the valve installation, repair, maintenance and other methods, there are structural characteristics: the connection structure of the valve length and overall height, and pipeline (flange connection, threaded connections, clamp connections, threaded connections, welded connections etc.); the sealing surface of the form (ring, thread ring, welding, spray welding, valve body); stem structure (rotating rod and the lifting rod).

2. the steps and basis of the selection of the valve are as follows:

The selection step

(1) determine the use of the valve in the equipment or device, and determine the working conditions of the valve: the applicable medium, working pressure, working temperature and so on.

Determine the nominal diameter and connection mode of the pipe connecting with the valve: flange, thread, welding and so on.

(3) to determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electrohydraulic linkage.

According to the medium, working pressure and working temperature of the pipeline, the material of the shell and inner part of the selected valve is determined: gray iron, malleable iron, ductile iron, carbon steel, alloy steel, stainless acid resisting steel and copper alloy.

Selection of valve types: closed valve, regulating valve, safety valve and so on.

To determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam traps, etc..

The determination of the parameters of the valve: the valve automatically, depending on the need to determine the allowable flow resistance, discharge capacity, back pressure, and then determine the nominal pipe diameter and the valve seat hole diameter.

The valve used to determine the geometric parameters: the length of the structure, form and size of flange connection, opening and closing the valve after the height direction of the size of the connection bolt hole size and quantity, the entire valve dimensions etc..

Use of existing information: valve product catalog, product samples and other valves select the appropriate valve products.

The choice of understand the steps in the selection valve while the valve on the basis of further understanding should also select the valve according to.

(1) the use of the selected valves, operating conditions and control mode.

(2) the nature of working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, the viscosity of the medium, etc.

(3) requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, seal grade and so on.

The dimensions and dimensions of the installation are required: the nominal diameter, the connection with the pipe and the size of the connection, the size of the shape or the weight limit.

The additional requirements for the reliability of the valve products, the service life and the explosion-proof performance of the electric devices.

When selecting parameters, it should be noted that if the valve is to be used for control purposes, the following additional parameters must be determined: operation method, maximum and minimum flow requirement, normal flow pressure drop, pressure drop at closing time, maximum and minimum inlet pressure of valve.

According to the basis and steps of selecting valve above, we must know more about the internal structure of various valves when we choose the valve correctly and correctly, so that we can make the right choice for the priority valve.

The final control of the pipe is the valve. The valve opening and closing controls the flow of the medium in the pipe. The shape of the valve channel makes the valve have a certain flow characteristic and is selected in the selection of the pipe.