Reasonable selection of valves
The gate valve is used as a cut-off medium, and the whole flow is straight when it is fully opened. At this time, the pressure loss of the medium is minimal. Gate valves are usually suitable for working conditions that do not need to be opened and closed frequently and keep the gate fully open or fully closed. Not suitable for use as regulation or throttling. For the high-speed flowing medium, the gate can cause vibration of the gate when it is partially opened, and the vibration may damage the sealing surface of the gate and the valve seat, and the throttling will cause the gate to be eroded by the medium. From the structural form, the main difference is the form of the sealing element used. 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.
The stem axis of the stop valve is perpendicular to the sealing surface of the valve seat. The opening or closing stroke of the valve stem is relatively short, and it has a very reliable cut-off action, making this valve very suitable for the cut-off or adjustment and throttling of the medium. Once the valve disc of the shut-off valve is in the open condition, there is no longer contact between its valve seat and the sealing surface of the valve disc, and it has a very reliable cut-off action. This kind of valve is very suitable for cutting or adjusting and reducing the medium. Stream usage.
Once the shut-off valve is in the open state, there is no longer contact between its seat and the sealing surface of the disc, so its sealing surface is less mechanically worn, because most of the valve seats and discs are easier to repair or replace It is not necessary to remove the entire valve from the pipeline when sealing the components, which is very suitable for the occasion where the valve and the pipeline are welded together. The flow direction of the medium through this type of valve has changed, so the flow resistance of the stop valve is higher than that of other valves.
The commonly used globe valves are as follows:
1) Angle type stop valve; in the angle type stop valve, the fluid only needs to change its direction once, so that the pressure drop through this valve is smaller than that of the conventional structure of the stop valve.
2) Direct-flow stop valve; in direct-flow or Y-shaped stop valve, the flow passage of the valve body is in a diagonal line with the main flow passage, so that the degree of damage to the flow state is smaller than that of the conventional stop valve, so the pressure loss through the valve is also corresponding Is too small.
3) Plunger type globe valve: This type of globe valve is a variation of the conventional globe valve. In this valve, the disc and valve seat are usually designed based on the plunger principle. The valve clack is polished so that the plunger is connected to the valve stem, and the sealing is achieved by two elastic sealing rings sleeved on the plunger. The two elastic sealing rings are separated by a sleeve ring, and the sealing ring around the plunger is pressed firmly by the load exerted on the bonnet by the bonnet nut. The elastic sealing ring can be replaced and can be made of various materials. The valve is mainly used for “open” or “close”, but it is equipped with a special form of plunger or special collar, which can also be used to adjust the flow rate. .
The butterfly plate of the butterfly valve is installed in the diameter direction of the pipe. In the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When the rotation reaches 90°, the valve is fully opened.
The butterfly valve is simple in structure, small in size and light in weight, and consists of only a few parts. Moreover, it can be opened and closed quickly by rotating 90°, and the operation is simple. 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, so the pressure drop generated by the valve is small, so it has better flow control characteristics. The butterfly valve has two sealing types: elastic seal and metal seal. Elastic sealing valve, the sealing ring can be inlaid on the valve body or attached to the periphery of the butterfly plate. To
Valves with metal seals generally have a longer life than valves with elastic seals, but it is difficult to achieve a complete seal. The metal seal can adapt to higher working temperature, while the elastic seal has the defect of being limited by temperature.
If the butterfly valve is required to be used as a flow control, the main thing is to correctly select the size and type of the valve. The structure principle of butterfly valve is especially suitable for making large-diameter valves. Butterfly valves are not only widely used in general industries such as petroleum, gas, chemical, water treatment, etc., but also used in cooling water systems of thermal power stations.
Commonly used butterfly valves include wafer type butterfly valves and flange type butterfly valves. Wafer type butterfly valve uses double-head bolts to connect the valve between two pipe flanges. Flange type butterfly valve has flanges on the valve, and bolts are used to connect the flanges at both ends of the valve to the pipe flanges.
The ball valve evolved from the plug valve. It has the same lifting action by rotating 90 degrees, but the difference is that the cock body is a sphere with a circular through hole or channel passing through its axis. The ratio of the spherical surface to the channel opening should be such that when the ball rotates 90 degrees, all the spherical surfaces should be present at the entrance and exit, thereby cutting off the flow.
The ball valve can be closed tightly with only a 90-degree rotation and a small torque. The completely equal internal cavity of the valve provides a straight flow channel with little resistance for the medium. It is generally believed that the ball valve is most suitable for direct opening and closing, but recent developments have designed the ball valve to throttle and control the flow. The main feature of the ball valve is its compact structure, easy operation and maintenance, suitable for general working media such as water, solvent, acid and natural gas, and also suitable for media with harsh working conditions, such as oxygen, hydrogen peroxide, and ethylene. The ball valve body can be integral or combined.
Select the valve to prevent the medium from flowing back.
The function of this type of valve is to only allow the medium to flow in one direction, and to prevent the flow of the direction. Usually this kind of valve works automatically. Under the action of the fluid pressure flowing in one direction, the valve flap opens; when the fluid flows in the opposite direction, the fluid pressure and the self-coincidence of the valve flap act on the valve seat, thereby cutting off the flow. Among them, 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 valve disc like a door that rests freely on the inclined valve seat surface. In order to ensure that the valve clack can reach the proper position of the valve seat surface every time, the valve clack is designed in a hinge mechanism so that the valve clack has enough space for turning and makes the valve clack truly and comprehensively contact the valve seat. The valve clack can be made of metal, leather, rubber, or synthetic covering can be inlaid on the metal, depending on the performance requirements. 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 valve disc of the lift check valve is seated on the sealing surface of the valve seat on the valve body. Except that the disc can be raised and lowered freely, the rest of the valve is like a shut-off valve. The fluid pressure lifts the disc from the seat sealing surface, and the backflow of the medium causes the disc to fall back onto the seat and cut off the flow. According to the conditions of use, the valve clack can be an all-metal structure, or it can be in the form of a rubber pad or a rubber ring inlaid on the valve clack frame. Like a shut-off 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 rate of the swing check valve is restricted. rare.
Select the valve according to the adjustment medium parameters
In the production process, in order to make the parameters such as the pressure and flow of the medium meet the requirements of the technological process, it is necessary to install an adjustment mechanism to adjust the above parameters. The main working principle of the adjustment mechanism is to achieve the purpose of adjusting the above parameters by changing the flow area between the valve disc and the valve disc and the valve seat. These types of valves are collectively referred to as control valves, which are divided into self-driving control valves such as pressure reducing valves and stabilizing valves that rely on the power of the medium itself. Power) is called other drive control valve, such as electric control valve, pneumatic control valve and hydraulic control valve, etc.