How to choose a suitable valve?

2018-05-02 17:33:15 118

In the fluid pipeline system, the valve is the control element, its main function is to isolate the equipment and the pipe system, adjust the flow rate, prevent reflux, adjustment and discharge pressure. It can be used to control the flow of all kinds of fluids such as air, water, steam, corrosive media, mud, oil, liquid metal and radioactive medium. Since the selection of the most suitable valve for the pipe system is very important, it is also important to understand the characteristics of the valve and the steps and basis of the selection of the valve.

Classification of valves

One, the total of the valves can be divided into two major categories:

Type 1 automatic valve: valve operated by the medium (liquid, gas) itself.

Such as check valve, safety valve, regulating valve, steam trap, pressure reducing valve and so on.

The second type of drive valve: manual, electric, hydraulic, pneumatic to control the operation of the valve.

Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, cock valve and so on.

Two. According to the structural characteristics, according to the direction of the closing piece moving relative to the seat, it can be divided into:

1. closure: the closure moves along the seat center;

2. gate shape: the closure parts move along the center of the vertical valve seat.

3. cock and ball: the closure is a plunger or ball, revolving around the centerline of itself.

4. swirling shape: the revolving part revolves around the axle outside the valve seat.

5. dish shape: the disc of the closing piece revolves around the axis of the valve seat.

6. slide valve shape: the closure piece slides in the direction perpendicular to the channel.

Three, according to the purpose, according to the different uses of the valve, it can be divided into:

1. break use: used to connect or cut off pipeline medium, such as globe valve, gate valve, ball valve, butterfly valve and so on.

2. stop use: to prevent backflow of media, such as check valves.

3. regulation: used to regulate the pressure and flow of medium, such as regulating valve and pressure reducing valve.

4. allocation: used to change the flow direction of the medium and distribute the medium, such as three way cock, distributing 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 steam trap, vent valve, drain valve and so on.

Four, according to the driving mode, according to different driving modes, it can be divided into:

1. Manual: with handwheel, handle, lever or sprocket, it has manpower drive, and the larger torque fashion has worm gear and gear reducer.

2. Electric: motor or other electrical devices to drive.

3. fluid movement: driven by (water and oil).

4. air movement: driven by compressed air.

Five, according to the pressure, according to the nominal pressure of the valve can be divided into:

1. vacuum valve: absolute pressure <0.1Mpa or 760mm high mercury valve, usually using mm mercury column or mm water column to indicate pressure.

2. low pressure valve: nominal pressure PN or less than 1.6Mpa valve (including steel valve of PN less than 1.6MPa)

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 or more than 100.0MPa valve.

Six. According to the temperature of the medium, according to the medium temperature of the valve, it can be divided into:

1. ordinary valves: suitable for medium temperature -40 to 425 degrees.

2. high temperature valve: suitable for medium temperature 425 to 600 degrees.

3. heat resistant valve: suitable for medium temperature above 600 degree.

4. cryogenic valve: suitable for medium temperature -150 to -40 degrees.

5. ultra low temperature valve: suitable for medium temperature -150 degrees below the valve.

Seven. According to the nominal diameter, according to the nominal diameter of the valve, it can be divided into:

1. small caliber valve: nominal diameter DN<40mm valve.

2. medium caliber valve: nominal diameter DN50 ~ 300mm valve.

3. large caliber valves: nominal diameter DN350 ~ 1200mm valves.

4. large diameter valve: nominal diameter DN or less than 1400mm valve.

Eight. According to the way of connection with the pipeline, according to the connection mode between the valve and the pipeline, it can be divided into:

1. flanged valves: valves with flanges and flanges connected to pipes.

2. threaded connection valve: valve with internal thread or external thread, threaded connection with the pipeline valve.

3. welding connection valve: valve body with welding port and welded pipe connection valve.

4. clip hoop connection valve: the valve body is provided with a clamping port, and the valve is connected with the pipe by a clamp.

5. card sleeve connection valve: the valve is connected by a sleeve and pipe.

The characteristics of the valve

There are two general characteristics of valves, service characteristics and structural characteristics.

Use characteristics: it determines the main performance and scope of the valve, belonging to the valve characteristics: valve categories (closed valve, regulating valve, safety valve, etc.); product type (gate valve, cut-off valve, butterfly valve, ball valve, etc.); valve main parts (valve body, valve cover, stem, valve, seal) Material of surface); valve transmission mode, etc.

Structural characteristics: it identifies some structural characteristics of the installation, maintenance, and maintenance of the valve, which are structural characteristics: the structure length and overall height of the valve, the form of the connection with the pipe (flange connection, threaded connection, clamp connection, external thread connection, welding end connection, etc.); the form of the sealing surface (inlaid) Ring, thread ring, surfacing, spray welding, valve body), valve stem structure (rotating rod, lifting lever).

The steps and basis of the selection of the valve

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