Thread Content
This article will provide a detailed overview of the selection of 5 common types of valves. Readers can choose the most suitable valve based on their own operational conditions. Gate valves are used to stop the flow of media; when fully open, the flow path is completely unobstructed, resulting in the lowest pressure loss for the media flowing through it. Gate valves are typically suitable for applications where frequent opening and closing are not required, and where the gate plate needs to remain fully open or fully closed. Not suitable for use as a regulator or throttle. For media flowing at high speeds, partial opening of the gate can cause vibration in the valve, and this vibration may damage the sealing surfaces of the gate and the valve seat; moreover, throttling exposes the gate to erosion by the medium. In terms of structural form, the main difference lies in the type of sealing element used. Based on the design of the sealing element, gate valves are often classified into several different types, such as wedge gate valves, parallel gate valves, parallel double-plate gate valves, and wedge double-plate gate valves. The most commonly used types are wedge gate valves and parallel gate valves. Stop valve: The axis of the stem of a stop valve is perpendicular to the sealing surface of the valve seat. The opening or closing stroke of the valve stem is relatively short. Once the disc of a globe valve is in the open position, there is no longer any contact between its seat and the sealing surface of the disc; as a result, mechanical wear on these sealing surfaces is minimal. Since the seats and discs of most globe valves are relatively easy to repair, it is not necessary to remove the entire valve from the pipeline when replacing the sealing elements. This is particularly advantageous in cases where the valve is welded to the pipeline. These features make globe valves highly suitable for shutting off, regulating, or throttling fluids. When the medium passes through such valves, the flow direction changes. Therefore, the flow resistance of a globe valve is higher than that of other valves. The common types of globe valves are as follows: 1. Angle-type globe valve. In an angle-type globe valve, the fluid only needs to change direction once; as a result, the pressure acting on this type of valve is lower than that in globe valves with conventional designs. 2. Direct-flow globe valve: In direct-flow or Y-type globe valves, the flow path of the valve body forms an angle with the main flow direction; as a result, the degree of disruption to the flow pattern is less compared to conventional globe valves. Consequently, the pressure loss across the valve is also lower. 3. Plunger-type globe valve: This type of globe valve is a variant of the conventional globe valve. In such valves, the valve disc and seat are typically designed based on the plunger principle. The valve disc is polished to form a plunger that is connected to the valve stem, and sealing is achieved by two elastic sealing rings fitted over the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings surrounding the plunger are pressed in place by the load applied to the valve cover via the valve cover nut. The elastic sealing ring can be replaced and is made from various materials. This valve is primarily used for opening or closing, but with special-shaped plungers or special rings, it can also be used to regulate flow. Butterfly valve: The butterfly disc of a butterfly valve is installed in the diameter direction of the pipeline. Within the cylindrical passage of the butterfly valve body, a disc-shaped butterfly plate rotates around an axis, with the rotation angle ranging from 0 to 90 degrees; when it reaches 90 degrees, the valve is in its fully open position. Butterfly valves feature a simple structure, are small in size, light in weight, and consist of only a few components. Moreover, it can be quickly opened and closed by simply rotating 90 degrees, making the operation simple; at the same time, this valve boasts excellent fluid control properties. When the butterfly valve is in its fully open position, its thickness represents the only resistance to the flow of the medium through the valve body; therefore, the pressure drop resulting from passage through this valve is very small. Butterfly valves come in two types of sealing: elastic sealing and metal sealing. Elastic-sealing valves, where the sealing ring can be embedded in the valve body or around the butterfly plate in its vicinity. Valves with metal seals generally have a longer lifespan than those with elastic seals, but it is difficult to achieve complete sealing. Metal seals can withstand higher operating temperatures, while elastic seals have the drawback of being limited by temperature. If a butterfly valve is to be used for flow control, the most important thing is to select the correct size and type of valve. The structural principle of butterfly valves makes them particularly suitable for manufacturing large-diameter valves. Butterfly valves are widely used not only in general industries such as petroleum, gas, chemicals, and water treatment, but also in the cooling water systems of thermal power plants. The commonly used butterfly valves are wafer-type butterfly valves and flanged butterfly valves. The wafer-type butterfly valve is one in which the valve is connected between the flanges of two pipes using double-headed bolts. A flanged butterfly valve is a valve equipped with flanges, using bolts to connect the flanges at both ends of the valve to the pipe flanges. Ball valve: The ball valve evolved from the rotary valve. It has the same 90-degree rotation action; the difference is that the plug body is spherical, with a circular hole or passage running through its axis. The ratio between the sphere and the opening should be such that when the sphere rotates 90 degrees, the entire area at the inlet and outlet should be covered by the sphere, thereby blocking the flow. A ball valve can be closed tightly with just a 90-degree rotation and very little torque. A safe and equal internal valve chamber provides a flow path with very low resistance and a direct route for the medium. It is generally believed that ball valves are most suitable for direct on-off operation, but recent developments have designed ball valves to also serve the purpose of throttling and controlling flow rates. The main advantages of ball valves are their compact structure, ease of operation and maintenance. They are suitable for use with common working media such as water, solvents, acids, and natural gas, as well as for media under harsh operating conditions, such as oxygen, hydrogen peroxide, methane, and ethylene. The ball valve body can be integral or modular. Check valve: A check valve allows the fluid to flow in only one direction, preventing flow in the opposite direction. Normally, a check valve operates automatically; the valve disc opens under the pressure of fluid flowing in one direction ； When the fluid flows in the opposite direction, the fluid pressure, together with the weight of the valve disc and the force exerted by the valve disc on the valve seat, causes the flow to be interrupted. Check valves include swing check valves and lift check valves. A swing check valve has a pivot hinge mechanism, as well as a valve disc that resembles a door and rests freely on an inclined valve seat surface. To ensure that the valve disc reaches the appropriate position on the valve seat surface each time, it is mounted on a hinge mechanism, which provides sufficient space for it to swing open and allows the valve disc to make full and complete contact with the valve seat. The valve disc can be made entirely of metal, or leather, rubber, or synthetic covers can be embedded in metal, depending on the requirements for performance. When a swing check valve is fully open, the fluid pressure encounters little resistance; therefore, the pressure drop across the valve will be low. The disc of the lift-type check valve is seated on the seat sealing surface of the valve body. Apart from the valve disc, which can move up and down freely, this valve operates in a similar manner to a globe valve: fluid pressure lifts the valve disc off the sealing surface of the valve seat, while backflow causes the valve disc to drop back onto the valve seat, thereby stopping the flow. Depending on the applicable conditions, the valve disc can be a fully metal structure, or it can be equipped with rubber gaskets or rubber rings mounted on the valve disc frame. Like globe valves, the flow passage through lift check valves is also narrow; therefore, the pressure drop across lift check valves is greater than that across swing check valves, and the flow rate of swing check valves is subject to fewer restrictions. Select valves based on the parameters of the medium. During the production process, in order to ensure that parameters such as the pressure and flow rate of the medium meet the requirements of the manufacturing process, control mechanisms need to be installed to adjust these parameters. The main working principle of the regulating mechanism is to change the flow area between the valve disc and the valve seat, thereby adjusting the aforementioned parameters. Valves of this type are collectively referred to as control valves. Those that are driven by the power of the medium itself are called self-acting control valves, such as pressure reducing valves and pressure stabilizing valves. Those that are driven by external sources of power, such as electricity, compressed air, or hydraulic force, are called externally driven control valves, such as electric control valves, pneumatic control valves, and hydraulic control valves.