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Complete selection of knowledge of valve
May 17, 2018

1. Select the valve according to the adjusting medium parameters.

In the process of production, in order to make the pressure and flow of medium conform to the requirements of the process, it is necessary to install adjusting mechanism to adjust the above parameters. The main principle of the adjusting mechanism is to change the flow area between the valve disc and the disc and the valve seat so as to achieve the purpose of adjusting the parameters mentioned above. This type of valve is called control valve, which is divided into self drive control valves, such as pressure relief valve, pressure regulator, and so on, which are driven by the medium itself, such as power, compressed air and hydraulic power, such as electric control valve, pneumatic regulating valve and hydraulic regulating valve.

Two. Select the valve according to the reverse medium reflux.

The purpose of this type of valve is to allow the medium to flow in one direction and to prevent directional flow. Usually, the valve is operated automatically. The valve opens under the flow of fluid pressure in one direction; the fluid pressure and the self gravity valve disc of the valve act on the seat when the fluid flows in reverse direction, thus cutting off the flow. The check valve belongs to this type of valve, which includes swing check valve and lift check valve. The swing check valve has a hinge mechanism, and a door like valve flap freely on the inclined seat surface. In order to ensure that the valve can reach the appropriate position of the seat each time, the valve disc is designed in the hinge mechanism so that the disc has enough space to swing, and the valve is truly and fully contact with the seat. The disc can be made of metal or leather, rubber or synthetic coverage on the metal, depending on the performance requirements. When the swing check valve is fully open, the pressure of the fluid is almost unhindered, so the pressure drop through the valve is relatively small. The valve of the lift check valve is located on the valve seat sealing surface of the valve body. In addition to the free lift of the valve, the rest of the valve is like a cut-off valve. The fluid pressure makes the valve lift from the seat seal surface, and the reflux of the medium causes the valve to fall back to the seat and cut off the flow. According to the use conditions, the solenoid valve disc can be a metal structure, or a rubber gasket or rubber ring on the valve frame. Like the cut-off valve, the flow of the fluid through the lift check valve is also narrow, so the pressure drop of the lift check valve is larger than the swing check valve, and the flow of the swing check valve is limited.

Three. Select the valve according to the properties of the medium.

1. gate valve: the gate valve is used as cut-off medium, and the whole flow is straight through at full opening. At this time, the pressure loss of medium operation is minimal. Gate valves are usually applied to do not require frequent opening and closing, and maintain full or full closing of the gate. The gate valve produced by Shanghai Xing Ou valve is not suitable for regulating or throttling use. For the high-speed flow medium, the gate can cause the vibration of the gate under the condition of local opening, and the vibration may damage the seal surface of the gate and the valve seat, and the throttle will cause the gate to suffer the erosion of the medium. From the structural form, the main difference is the form of the sealing element used. According to the form of sealing elements, the gate valves are often divided into several different types, such as wedge-shaped gate valve, parallel gate valve, parallel double gate valve, wedge type double gate sluice and so on. The most commonly used forms are wedge gate valves and parallel gate valves.

2. the stem axis of the globe valve is perpendicular to the sealing surface of the valve seat. The opening or closing of the valve stem of the diaphragm valve is relatively short, and has a very reliable cutting action, making the valve very suitable for cutting or adjusting and throttle use of the medium. When the valve is in the open condition, the valve seat and the valve seal face no longer contact, and have a very reliable cutting action, so that the valve is very suitable to be used as a medium to cut off or adjust and throttle. Once the valve is open, the valve seat and the valve seal face are no longer in contact, so the mechanical wear of the sealing surface is small. Because most of the valve seats and valves are easier to repair or replace the sealing element, the whole valve is not removed from the pipeline, which is welded to the valve and the pipeline. The occasion is very applicable. The flow direction of the valve medium changes through such valves, so the flow resistance of the globe valve is higher than that of other valves.

The commonly used cut-off valves are the following:

1) angle stop valve: in the angle stop valve, the fluid needs to be changed only once, so that the pressure through this valve is smaller than that of the conventional structure.

2) DC shut-off valve: in the DC or Y type cut-off valve, the flow channel of the valve body is a slash line with the main channel, so the flow state is less damaged than the conventional cut-off valve, so the pressure loss through the valve is also smaller.

3) plunger stop valve: this type of globe valve is a variant of the conventional cut-off valve. In this valve, disc and valve seat are usually designed based on plunger principle. The disc is burnished and the plug is connected with the stem. The seal is realized by two elastic seals on the plunger. The two elastic sealing rings of the plug valve are separated by a ring, and the sealing ring around the plunger is pressed through the load exerted on the valve cover by the bonnet nut. The elastic sealing ring can be replaced and can be made of all kinds of materials. The valve is mainly used for opening or closing, but with a special type of plunger or special ring, it can also be used to adjust the flow.

3. butterfly valve: butterfly valve's butterfly plate is installed in the diameter direction of the pipe. In the cylindrical channel of the butterfly valve body, the disc butterfly plate rotates around the axis and the angle of rotation is between 0 degrees ~90 degrees, and the valve is in full open state when it is rotated to 90 degrees. Butterfly valve is simple in structure, small in size and light in weight. It consists of only a few parts. And it can be opened and closed quickly only by rotating 90 degrees. The operation is simple and the valve has good fluid control characteristics. When the butterfly valve is in full opening position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body. Therefore, the pressure drop produced through the valve is very small, so it has a better flow control characteristic.

Butterfly valve has two types of sealing: Bullet seal and metal seal.

The elastic sealing valve can be inlaid on the valve body or attached to the periphery of the butterfly plate. Metal seal can adapt to higher working temperature, and the elastic seal has the defect of temperature limitation. If butterfly valve is used as flow control, the size and type of valve should be chosen correctly. The structural principle of butterfly valve is especially suitable for making large caliber valves. Butterfly valves are widely used not only in petroleum, gas, chemical industry, water treatment and other general industries, but also in cooling water systems of thermal power stations.

There are two kinds of butterfly valves commonly used for butterfly valves and butterfly valves.

The clamp butterfly valve is a double head bolt connecting the valve to the two pipe flanges. The plunger valve flange butterfly valve is a flange with a bolt connecting the flanges on the two ends of the valve on the pipe flange.

4. ball valve: the ball valve is evolved from the cock valve. It has the same rotation 90 degrees lifting action, the difference is that the cock body is a sphere, a circular through hole or a passage through its axis. That is to say, when the ball rotates at 90 degrees, the sphere should be presented at the inlet and outlet, thus cutting off the flow. The ball valve can only be closed with 90 degrees of rotation and very small torque. Perfectly equal valve body cavity provides a very small and direct flow passage for the medium. Shanghai star Ou valve professional staff think that the ball valve is the most suitable for open and close use, but the recent development has designed the ball valve to make it throttle and control the flow of use. The main characteristic of the ball valve is its compact structure, easy operation and maintenance. It is suitable for water, solvent, acid and natural gas. It is also suitable for the medium with bad working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be integral or modular.