The difference between knife gate valve and globe valve

Their main differences are:

1. The structure is different. The structure of the knife gate valve is more complicated than that of the globe valve, and the height dimension is larger. From the appearance, the knife gate valve is shorter and taller than the globe valve. Attention.

2. The sealing surfaces are different. When the knife gate valve is opened and closed, the valve core and the sealing surface of the valve seat are always in contact and rub against each other, so the sealing surface is easy to wear, especially when the valve is close to the closed state, the pressure difference between the front and rear of the valve core is large, and the sealing surface wears even more Serious; once the disc of the globe valve is in the open state, there will be no contact between its valve seat and the sealing surface of the valve disc, so the mechanical wear of its sealing surface is small, but if the medium contains solid particles, it is easy to damage the seal noodle. The sealing surface of the knife gate valve has a certain self-sealing ability, and its valve core is tightly contacted with the sealing surface of the valve seat by the medium pressure to achieve tightness. The spool slope of the wedge-shaped knife gate valve is generally 3 to 6 degrees. When the spool is forced to close excessively or the temperature changes greatly, it is easy to get stuck. Therefore, the high temperature and high pressure wedge knife gate valve has adopted certain measures to prevent the valve core from being stuck in the structure. The sealing surface of the globe valve must be forced to close to achieve sealing. Under the same caliber, working pressure and the same driving device, the driving torque of the globe valve is 2.5~3.5 times that of the knife gate valve. This point should be paid attention to when adjusting the torque control mechanism of the electric valve. The sealing surface of the stop valve only contacts each other when it is completely closed. The relative slip between the forced closed valve core and the sealing surface is very small, so the wear of the sealing surface is also very small. The wear of the sealing surface of the globe valve is mostly due to the debris in front of the valve core and the sealing surface, or the high-speed erosion of the medium due to the loose closing state.

3. The flow resistance is different. When the knife gate valve is fully open, the entire flow channel is straight through. At this time, the pressure loss of the medium is the smallest. Compared with the globe valve, its main advantage is that the fluid flow resistance is small. The flow resistance coefficient of the ordinary knife gate valve is about 0.08~0.12. The resistance coefficient of ordinary globe valve is about 3.5~4.5. The opening and closing force is small. Knife gate valves are usually suitable for the working conditions that do not need to be opened and closed frequently, and keep the gate fully open or fully closed, and are not suitable for adjustment and throttling. However, the flow resistance of the stop valve is very large in the whole stroke, the unbalanced force is large, and the required driving force or torque is correspondingly much larger. But it is very suitable for regulating and throttling fluid. For high-speed flowing medium, when the gate is partially opened, it can cause the valve to vibrate, and the vibration may damage the sealing surface of the gate and the valve seat, and throttling will cause the gate to be eroded by the medium.

4. The flow direction is different. When the globe valve is installed, the medium can enter from the bottom of the valve core and from the top. The advantage of the medium entering from the bottom of the valve core is that the packing is not under pressure when the valve is closed, which can prolong the service life of the packing and replace the packing when the pipeline in front of the valve is under pressure. The disadvantage of the medium entering from the bottom of the valve core is that the driving torque of the valve is relatively large, which is about 1.05~1.08 times that of entering from the top, and the axial force on the valve stem is large, so the valve stem is easy to bend. For this reason, the method of medium entering from the bottom is generally only suitable for small-diameter stop valves (below DN50), and the way of medium flowing in from above is used for stop valves above DN200. The electric globe valve generally adopts the way that the medium enters from above. The disadvantage of the medium entering from above is just the opposite of that entering from below. The flow direction of the knife gate valve has the same effect from both sides. Compared with the knife gate valve, the globe valve has the advantages of simple structure, good sealing performance, and convenient manufacture and maintenance; the disadvantage is that the liquid resistance is large, and the opening and closing force is large.

5. The itinerary is different. The stroke of the knife gate valve is larger than that of the globe valve.

6. The maintenance process is different. The maintenance of the knife gate valve is not suitable for on-site pipelines, and the valve seat and disc of most globe valves can be replaced online without removing the entire valve from the pipeline. , is very suitable. Of course, there are more than these differences between knife gate valves and globe valves. In the selection and use, we must distinguish their similarities and differences well to avoid mistakes. The application range of globe valve and knife gate valve is determined according to their characteristics. In smaller passages, when better shut-off sealing is required, globe valves are often used; in steam pipes and large-diameter water supply pipes, knife gate valves are used because the fluid resistance is generally required to be small.