How to reasonably select valves according to mediu

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How to reasonably select valves according to the characteristics of media

I. select the valve according to the on-off property of the medium:

1. Gate valve:

the gate valve is used as the cut-off medium. When it is fully opened, the whole flow is straight, and the pressure loss of the medium operation is the smallest. Gate valves are usually suitable for working conditions that do not require frequent opening and closing, and keep the gate fully open or fully closed. It is not suitable for use as regulation or throttling. For high-speed flowing media, the ram can cause the vibration of the gate when it is partially opened, and the vibration may damage the sealing surface of the ram and the valve seat, and throttling will cause the ram to be eroded by the media. From the structural form, the main difference is the form of sealing elements. According to the form of sealing elements, gate valves are often divided into several different types, such as wedge gate valve, parallel gate valve, parallel double gate valve, wedge double gate valve, etc. The most commonly used forms are wedge gate valves and parallel gate valves

2. Stop valve:

the stem axis of the stop valve is perpendicular to the sealing surface of the valve seat. The valve rod has a relatively short opening or closing stroke and a very reliable cut-off action, which makes this valve very suitable for cutting off or adjusting and throttling as a medium

once the disc of the stop valve is in the open state, its seat and the sealing surface of the disc will no longer be in contact, and it has a very reliable cut-off action, so this valve is very suitable for cutting off or adjusting and throttling as a medium

once the stop valve is in the open state, there is no contact between its valve seat and the sealing surface of the valve disc, so its sealing surface has less mechanical wear. Because most of the valve seats and valve discs of the stop valve are relatively easy to repair or replace the sealing elements, there is no need to remove the whole valve from the pipeline, which is very suitable for the occasions where the valve and pipeline are welded together. When the medium passes through such valves, the flow direction changes, so the flow resistance of the stop valve is higher than that of other valves

there are several commonly used stop valves: 1) angle stop valve; In the angle stop valve, the fluid only needs to change the direction once, so that the pressure drop through this valve is smaller than that of the conventional stop valve. 2) DC stop valve; In the once through or Y-shaped stop valve, the flow passage of the valve body forms an oblique line with the main flow path, so the damage degree of the flow state is smaller than that of the conventional stop valve, so the pressure loss through the valve is correspondingly smaller. 3) Plunger stop valve: this type of stop valve is a variant of the conventional stop valve. In this valve, the disc and seat are usually designed based on the plunger principle. The valve disc is polished into a column plug and connected with the valve rod. The sealing is realized by two elastic sealing rings sleeved on the plunger. The two elastic sealing rings are separated by a collar, and the sealing ring around the plunger is firmly pressed by the load applied on the bonnet by the bonnet nut. The elastic seal ring can be replaced and made of various materials. The valve is mainly used for "opening" or "closing", but it is equipped with a special plunger or special collar, which can also be used to adjust the flow

3. Butterfly valve:

the butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0 ° ~90 °. When it rotates to 90 °, the valve is fully open

butterfly valve is simple in structure, small in size and light in weight. It is only composed of a few parts. Moreover, it can be opened and closed quickly by rotating 90 °, which is simple to operate. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body. Therefore, the pressure drop generated by the valve promotes the establishment of a regional emission reduction cooperation mechanism and trading systems such as energy saving, carbon emission rights, emission rights, water rights, etc., so it has good flow control characteristics. There are two sealing types of butterfly valve: elastic seal and metal seal, and the investment attraction is strengthened. For elastic sealing valves, the sealing ring can be embedded on the valve body or attached to the periphery of the butterfly plate

valves with metal seals generally have a longer service life than those with elastic seals, but it is difficult to achieve complete sealing. Metal seal can adapt to higher working temperature, while elastic seal has the defect of being limited by temperature

if the butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of the valve. The structural principle of butterfly valve is especially suitable for making large-diameter valves. Butterfly valves are not only widely used in petroleum, gas, chemical industry, water treatment and other general industries, but also used in the cooling water system of thermal power stations. There are two kinds of commonly used butterfly valves: wafer butterfly valve and flange butterfly valve. The wafer type butterfly valve connects the valve between two pipe flanges with studs. The flange type butterfly valve has flanges on the valve, and the flanges at both ends of the valve are connected to the pipe flanges with bolts. Imported pump valve industrial washing machine

4. Ball valve:

ball valve is evolved from plug valve. It has the same 90 degree rotation lifting action, but the difference is that the cock body is a sphere with a circular through hole or channel through its axis. The ratio of the sphere to the channel port should be such that when the sphere rotates 90 degrees, the sphere should be present at the inlet and outlet, so as to cut off the flow

the ball valve only needs to rotate 90 degrees and a small rotating torque to close tightly. The completely equal inner cavity of the valve body provides a small resistance and direct flow channel for the medium. It is generally believed that ball valves are most suitable for direct opening and closing, but recent developments have designed ball valves to have throttling and flow control functions. The main characteristics of the ball valve are its compact structure, easy operation and maintenance. It is suitable for general working media such as water, solvent, acid and natural gas, and also suitable for media with poor working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The valve body of ball valve can be integral or combined

second, select the valve according to the prevention of medium backflow:

the function of this type of valve is to only allow the medium to flow in one direction and prevent the flow in one direction. Usually, this kind of valve works automatically with tensile strength and deformation rate. Under the action of fluid pressure flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the fluid pressure and the self weight of the valve disc act on the valve seat to cut off the flow. The check valve belongs to this type of valve, which includes swing check valve and lift check valve. Swing check valve has a hinge mechanism, and a valve disc like a door freely rests on the inclined valve seat surface. In order to ensure that the valve clack can reach the appropriate position of the valve seat surface every time, the valve clack is designed in the hinge mechanism, so that the valve clack has enough swing space and makes the valve clack truly and comprehensively contact the valve seat. The valve disc can be made of metal, or inlaid with leather, rubber or synthetic coverage, depending on the requirements of service performance. When the swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The disc seat of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the valve disc can rise and fall freely, the rest of the valve is like a stop valve. The fluid pressure lifts the valve disc from the sealing surface of the valve seat, and the medium backflow causes the valve disc to fall back to the valve seat and cut off the flow. According to the service conditions, the valve disc can be of all metal structure, or it can be in the form of inlaying rubber pads or rubber rings on the valve disc frame. Like the stop valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow of the swing check valve is rarely limited

III. select valves according to the parameters of the regulating medium:

in the production process, in order to make the pressure, flow and other parameters of the medium meet the requirements of the process flow, it is necessary to install a regulating mechanism to adjust the above parameters. The main working principle of the regulating mechanism is to adjust the above parameters by changing the flow area between the valve disc and the valve seat. These valves are collectively referred to as control valves, which are divided into self driving control valves driven by the power of the medium itself, such as pressure reducing valves, pressure stabilizing valves, etc., and those driven by the leading power (such as electric power, compressed air and hydraulic power) are called other driving control valves, such as electric control valves, pneumatic control valves and hydraulic control valves

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