One Select valves according to the parameters of the regulating medium:
In the production process, in order to ensure that the pressure, flow rate, 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 disc and seat. The valves belonging to this category are collectively referred to as control valves, which are divided into self driven control valves such as pressure reducing valves and stabilizing valves that rely on the power of the medium itself. Any power driven valves (such as electric, compressed air, and hydraulic) are called other driven control valves, such as electric control valves, pneumatic control valves, and hydraulic control valves.
II Select valves to prevent medium backflow:
The function of this type of valve is to only allow the medium to flow in one direction and prevent directional flow. Usually, this type of valve works automatically, and under the pressure of fluid flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the pressure of the fluid and the self weight of the valve disc act on the valve seat, thereby cutting off the flow. Check valves belong to this type of valve, which includes swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve disc like a door that freely rests on the inclined valve seat surface. In order to ensure that the valve disc can reach the appropriate position on the valve seat surface every time, the valve disc is designed in a hinge mechanism so that the valve disc has sufficient swing space and truly and fully contacts the valve seat. The valve disc can be made entirely of metal, or it can be embedded with leather, rubber, or a synthetic cover on top of the metal, depending on the performance requirements. When the swing check valve is open, the fluid pressure is almost unobstructed, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except for the valve disc, which can be freely raised and lowered, the rest of this valve is like a globe valve. Fluid pressure lifts the valve disc from the sealing surface of the valve seat, causing the medium to reflux and causing the valve disc to fall back onto the valve seat, cutting off the flow. According to the usage conditions, the solenoid valve disc can be made of all metal structure or embedded with rubber pads or rubber rings on the disc holder. Like globe valves, the passage of fluid through lift check valves is also narrow, so the pressure drop through lift check valves is greater than that through swing check valves, and the flow of swing check valves is less restricted.
III Select valves based on the on-off properties of the medium:
1. Gate valve: Gate valves are used as shut-off media, and when fully opened, the entire flow is straight through, resulting in minimal pressure loss during the operation of the medium. Gate valves are usually suitable for working conditions that do not require frequent opening and closing, and keep the gate fully open or closed. The gate valves produced by Shanghai Xingou Valve are not suitable for use as regulating or throttling valves. For high-speed flowing media, when the gate is partially opened, it can cause vibration of the gate, which may damage the sealing surface of the gate and valve seat. Throttling can cause erosion of the gate by the medium. The main difference in structural form is the form of the sealing element used. According to the form of sealing components, gate valves are often divided into several different types, such as wedge gate valves, parallel gate valves, parallel double gate valves, wedge double gate valves, etc. The most commonly used forms are wedge gate valves and parallel gate valves.
The axis of the valve stem of the globe valve is perpendicular to the sealing surface of the valve seat. The diaphragm valve stem has a relatively short opening or closing stroke and reliable cutting action, making it suitable for use as a medium for cutting, regulating, and throttling. When the valve disc is in the open position, there is no longer contact between its valve seat and the sealing surface of the valve disc, and it has a reliable cutting action. Therefore, this type of valve is suitable for cutting off, regulating, and throttling media. Once the globe valve is in the open state, there is no longer contact between its valve seat and valve disc sealing surface, so its sealing surface has less mechanical wear. As most globe valves have valve seats and discs that are relatively easy to repair or replace, there is no need to remove the entire valve from the pipeline when replacing sealing components. This is very suitable for situations where the valve and pipeline are welded together. The flow direction of the drain valve medium changes when passing through this type of valve, so the flow resistance of the globe valve is higher than that of other valves.
There are several commonly used globe valves:
1) Angle globe valve: In an angle globe valve, the fluid only needs to change direction once, so that the pressure passing through this valve is lower than that of a conventional structure globe valve.
2) DC globe valve: In DC or Y-shaped globe valves, the flow path of the valve body forms a diagonal line with the main flow path, which reduces the degree of damage to the flow state compared to conventional globe valves, and therefore reduces the pressure loss through the valve.
3) Piston type globe valve: This type of globe valve is a variation of conventional globe valves. In this valve, the valve disc and seat are usually designed based on the plunger principle. The valve disc is polished into a plunger and connected to the valve stem, and the sealing is achieved by two elastic sealing rings fitted 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 firmly by the load applied to the valve cover by the valve cover nut. The elastic sealing ring can be replaced and made of various materials. This valve is mainly used for opening or closing, but it is equipped with a specially designed plunger or special ring, which can also be used to adjust the flow rate.
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 butterfly plate rotates around the axis, with a rotation angle between 0 ° and 90 °. When it rotates to 90 °, the valve is in a fully open state. Butterfly valves have a simple structure, small size, and light weight, consisting of only a few components. And it can be quickly opened and closed by simply rotating 90 °, with simple operation, and the valve has good fluid control characteristics. When the butterfly valve is in the * open position, the thickness of the butterfly plate is the resistance of the medium flowing through the valve body, so the pressure drop generated by this valve is very small, which has good flow control characteristics.
Butterfly valves have two sealing types: elastic sealing and metal sealing.
Elastic sealing valve, the sealing ring can be embedded on the valve body or attached around the butterfly plate. Metal seals can adapt to higher operating temperatures, while elastic seals have the drawback of being limited by temperature. If butterfly valves are required for flow control, it is mainly important to choose the correct size and type of valve. The structural principle of butterfly valves is particularly suitable for making large-diameter valves. Butterfly valves are not only widely used in general industries such as petroleum, gas, chemical, and water treatment, but also in the cooling water system of thermal power plants.
There are two commonly used butterfly valves: clamp type butterfly valve and flange type butterfly valve.
The clamp type butterfly valve is connected between two pipeline flanges with double headed bolts, while the plunger valve flange type butterfly valve has flanges on the valve, and the flanges on both ends of the valve are connected to the pipeline flange with bolts.
4. Ball valve: Ball valve evolved from plug valve. It has the same 90 degree rotation lifting action, but the difference is that the plug body is a sphere with a circular through-hole or channel passing through its axis. When the ball rotates 90 degrees, it should all appear spherical at the inlet and outlet, thus cutting off the flow. Ball valves can be tightly closed with only a 90 degree rotation and a small rotational torque. *The equal inner cavity of the valve body provides a low resistance and straight passage for the medium. Shanghai Xingou Valve personnel believe that ball valves are suitable for direct opening and closing, but recent developments have designed ball valves to have throttling and flow control functions. The main characteristics of ball valves are their compact structure, easy operation and maintenance, suitable for general working media such as water, solvents, acids, and natural gas, as well as for media with harsh working conditions such as oxygen, hydrogen peroxide, methane, and ethylene. The valve body of a ball valve can be integral or modular.