Difference between gate valves and globe valves (Repost)

Thread Content

Difference between gate valves and globe valves: 1. Different structures. Gate valves have a more complex structure than globe valves and are larger in height; in terms of appearance, gate valves are shorter but taller than globe valves. In particular, gate valves with visible stems require more vertical space, which is something to keep in mind when selecting a valve when installation space is limited. 2. The sealing surfaces are different. When a gate valve is opened and closed, the valve core and the sealing surface of the valve seat are in constant contact and experience friction against each other; as a result, the sealing surfaces tend to wear out, especially when the valve is in a nearly closed position, as the pressure difference across the valve core is high. In the case of globe valves, the wear on the sealing surfaces is even more severe ； 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. However, if the fluid contains solid particles, it can easily damage the sealing surfaces. The sealing surface of the gate valve has a certain degree of self-sealing capability; its valve core makes tight contact with the sealing surface of the valve seat under the pressure of the medium, thereby ensuring a leak-free seal. The slope of the valve core in wedge-shaped gate valves is generally 3 to 6 degrees; when the valve is forced to close excessively or there are large temperature changes, the valve core is prone to getting stuck. Therefore, high-temperature and high-pressure wedge gate valves are designed with certain measures to prevent the valve core from getting stuck. The sealing surface of a globe valve must be closed under forced force in order to achieve sealing; under the same diameter, operating pressure, and driving mechanism, the driving torque required for a globe valve is 2.5 to 3.5 times that of a gate valve. This point should be taken into account when adjusting the torque control mechanism of electric valves. The sealing surfaces of a globe valve come into contact with each other only when it is fully closed; the relative sliding distance between the valve stem, which is forced to close, and the sealing surfaces is very small, resulting in minimal wear of these sealing surfaces. The wear of the sealing surface on a globe valve is mostly caused by debris between the valve stem and the sealing surface, or by inadequate sealing in the closed position, which leads to high-speed erosion by the medium. 3. The flow resistance is different. When a gate valve is fully open, the entire flow path is unobstructed, resulting in the lowest pressure loss for the fluid as it flows. Compared to globe valves, its main advantage lies in the low resistance to fluid flow; the flow resistance coefficient of a typical gate valve is around 0.08–0.12, whereas that of a typical globe valve is around 3.5–4.5. The force required to turn it on and off is low. Gate valves are typically suitable for applications where frequent opening and closing are not required, and where the gate plate needs to remain either fully open or fully closed; they are not appropriate for use in regulating flow or throttling. The flow resistance of a globe valve remains high throughout its entire stroke, and due to the large unbalanced forces, the driving force or torque required for it is also significantly higher. But it is very suitable for regulating and throttling fluids. 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. 4. The flow directions are different. When installing a stop valve, the medium can enter either from below the valve core or from above. The advantage of allowing the medium to enter from below the valve core is that the packing is not under pressure when the valve is closed, which extends its service life; moreover, it is possible to replace the packing even when there is pressure in the pipeline ahead of the valve. The disadvantage of the medium entering from below the valve core is that the driving torque of the valve is higher, at about 1.05~1.08 times that of entry from above; the axial force on the valve stem is large, causing the stem to bend easily. For this reason, the method of allowing the medium to enter from below is generally only suitable for small-diameter globe valves (DN50 and below); for globe valves with a diameter of DN200 or more, the method of allowing the medium to flow in from above is used. Electric globe valves generally allow the medium to enter from above. The disadvantages of the medium entering from above are exactly the opposite of those of entering from below. For gate valves, the flow direction works the same whether it enters from either side. Compared to gate valves, globe valves have the advantages of a simple structure, good sealing performance, and ease of manufacturing and maintenance ； The downside is high fluid resistance and high force required to open and close it. 5. The itineraries are different. The stroke of a gate valve is greater than that of a globe valve. 6. The maintenance processes are different. The repair of gate valves is not suitable to be carried out on the pipelines in place, whereas the seat and disc of most globe valves can be replaced online without having to remove the entire valve from the pipeline. This is very appropriate in cases where the valve is welded to the pipeline. Of course, the differences between gate valves and globe valves go beyond these; when selecting and using them, it is important to clearly understand their similarities and differences in order to avoid mistakes. The application scope of globe valves and gate valves is determined by their characteristics. In smaller channels, where good shut-off sealing is required, globe valves are commonly used ； In steam pipes and large-diameter water supply pipes, gate valves are used because lower fluid resistance is generally required.