Nov.07.2024
The Globe Valve, also known as a sluice valve, belongs to the category of forced-sealed valves and is a type of shut-off valve. Connection Methods: Flanged Connection, Threaded Connection, Welded Connection.
Part 1 Principle of Operation for Globe Valve
The principle of a Globe Valve is to use the torque from the valve stem to apply pressure downward to the sealing surface. Then, relying on the pressure of the valve stem, the sealing surfaces of the valve disc and the valve seat are tightly fitted together to prevent the flow of the medium or to regulate the flow rate of the medium.
Part 2 Advantages of Low Inlet and High Outlet for Globe Valve
Generally, the installation direction of the Globe Valve requires a low inlet and high outlet. It should be installed according to the flow direction markings, and installation in the reverse direction should be avoided. Otherwise, when the Globe Valve is closed, pressure may remain in the valve chamber, causing the sealing on the valve cover to be under pressure and leading to external leakage of the valve. The main advantages include:
1) The design of the Globe Valve with a low inlet and high outlet aims to minimize flow resistance, making it easier to open the valve.
2) When the valve is closed, the gasket between the valve body and the bonnet, as well as the packing around the valve stem, are not under stress. This reduces the risk of long-term exposure to medium pressure and temperature, extends the lifespan, and reduces the chance of leakage.
3) It is possible to replace or add packing while the valve is closed, making maintenance easier.
Part 3 High Inlet and Low Outlet Situation for Globe Valve
The drawback of the medium entering from below the valve core is that the driving torque of the valve is larger, approximately 1.05~1.08 times that of the top-entry method. The axial force on the valve stem is greater, making it prone to bending. Therefore, the bottom-entry method is generally only suitable for small-diameter Globe Valves (DN50 and below), while Globe Valves with a diameter larger than DN200 typically have the medium enter from above.
Electric Globe Valves usually have the medium entering from above. The drawbacks of this top-entry method are opposite to those of the bottom-entry method.
In general design requirements, Globe Valves with a diameter (DN) of ≤200mm and a pressure rating (PN) of ≤4.0MPa use a low inlet and high outlet design. When the diameter is greater than 200mm, a high inlet and low outlet design is used. The valve disc of the Globe Valve is of a double-disc structure. For diameters larger than 200mm, due to the increased flow rate and pressure per unit area, a large counterforce is required to ensure sealing when using the low inlet and high outlet method. This necessitates a larger valve stem and the use of an impact handwheel or a high-torque worm gear device, increasing the size and cost of the valve, and the performance is not ideal.
High inlet and low outlet aid in sealing but make it more difficult to open due to overcoming the medium pressure. This method benefits sealing as the medium pressure makes the valve seal more tightly, improving the force conditions on the valve stem.
In conclusion, for valves with marked flow directions, they must be installed according to the indicated flow direction.
