The Main Difference And Use Of Knife Gate Valve And Globe Va
- 2020-06-18 11:12-
Knife gate valves and globe valves are the two most common shut-off valves.
The main differences are:
1. The flow resistance is different. When the knife gate valve is fully open, the entire flow passage is straight through. At this time, the pressure loss of the medium operation is the smallest. Compared with the globe valve, its main advantage is that the fluid flow resistance is small, and the flow resistance coefficient of the common knife gate valve is about 0.08~0.12. The resistance coefficient of the ordinary globe valve is about 3.5~4.5. The opening and closing force is small. Knife gate valves are generally suitable for use, do not need to open and close frequently, and keep the ram fully open or fully closed, not suitable for adjustment and throttling. The flow resistance of the shut-off valve is large throughout the stroke, the unbalanced force is large, and the required driving force or torque is correspondingly much larger. However, it is well suited for use as a conditioning and throttling fluid. For high-speed flowing media, the ram can cause vibration of the valve under partial opening conditions, and vibration may damage the sealing surface of the ram and the valve seat, and throttling will cause the ram to be eroded by the medium.
2. The flow is different. When the shut-off valve is installed, the medium can enter from the bottom of the spool and enter from above. The advantage of the medium entering from below the valve plug is that the packing is not under pressure when the valve is closed, the service life of the packing can be extended, and the packing can be replaced under pressure in front of the valve. The disadvantage of the medium entering from the lower side of the valve core is that the driving torque of the valve is relatively large, about 1.05~1.08 times of the upper entry, the axial force of the valve stem is large, and the valve stem is easy to bend. To this end, the medium enters the mode from below, generally only for small-diameter shut-off valves (below DN50), and the shut-off valves above DN200 use the medium to flow from above. Electric shut-off valves generally use a medium to enter from above. The disadvantage of the way the medium enters from above is exactly the opposite of the way it enters below. The flow direction of the knife gate valve is the same from both sides. Compared with the knife gate valve, the cut-off valve has the advantages of simple structure, good sealing performance and convenient manufacturing and maintenance; the disadvantage is that the liquid resistance is large, and the opening and closing forces are large.
3. The itinerary is different. The stroke of the knife gate valve is larger than that of the shutoff valve.
4. The maintenance process is different. The maintenance of the knife gate valve is not suitable for the pipeline on the site, and the valve seat and the valve flap of most of the globe valves can be replaced online, without removing the entire valve from the pipeline. This is where the valve and pipeline are welded together. , is very suitable. Of course, the difference between the knife gate valve and the globe valve is more than these. In the selection and use, we must distinguish their similarities and differences in order to avoid mistakes. The application range of the shut-off valve and the knife gate valve is determined according to its characteristics. In smaller passages, shut-off valves are often used when better shut-off sealing is required. In steam pipes and large-diameter water supply pipes, knife gate valves are used because fluid resistance is generally required to be small.
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