manual globe valve
Principle of globe valve
Simply put, the principle of the globe valve is to use the valve stem torque to exert downward pressure on the sealing surface, and rely on the valve stem pressure to make the valve disc sealing surface and the valve seat sealing surface closely fit to prevent the inflow of the medium or to adjust the flow rate of the medium. The opening and closing part of the globe valve is a cylindrical valve disc, the sealing surface is flat or conical, and the valve disc moves linearly along the center line of the fluid. The movement modes of the valve stem include the lifting rod type (the valve stem rises and falls, the handwheel does not rise and fall), and the lifting and rotating rod type (the handwheel and the valve stem rotate and rise together, and the nut is set on the valve body). The globe valve is a forced sealing valve, so when the valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak.
The working principle of the globe valve
We assume that there is a pipe with a cover. Water flows in from the bottom of the pipe and flows out toward the pipe mouth. The cover of the outlet pipe is equivalent to the closing member of the stop valve. If you lift the pipe cover upward by hand, the water will flow out. Covering the pipe will stop the flow of water, which is equivalent to the working principle of a globe valve.
The globe valve rotates the handwheel to raise and lower the valve stem, driving the valve disc to move linearly parallel to the flow direction of the medium to achieve the purpose of opening and closing. The handwheel rotates clockwise, and the working medium enters through the channel below the valve disc. At this time, the applied sealing force must be equal to or greater than the sum of the necessary specific pressure generated on the sealing surface and the upward force of the medium.
When the globe valve is opened, when the opening height of the valve disc is 25% to 30% of the nominal diameter, the flow rate has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the globe valve should be determined by the stroke of the valve disc.
Note:
1. The stop valve only allows the medium to flow in one direction, and there is a directionality during installation.
2. The function of the globe valve is either 0 or 1, either open or closed. In other words, the stop valve is only suitable for fully opening and fully closing, and adjustment and throttling are not recommended.
Structural principle
The centers of the inlet and outlet of the globe valve are located on the same straight line, and the fluid flows like an S-shaped sphere, so it is also called a spherical globe valve.
When the valve stem's seat moves downward toward the bottom sealing surface and presses it, the medium stops flowing; when the valve stem rises, the medium passes through the flow channel from below to the upper flow channel.
There are generally directional requirements when installing globe valves. The flow direction of the medium in the pipeline generally flows from bottom to top through the valve seat port, which is what we often call "low in, high". The purpose of this is to reduce fluid resistance and save effort when opening. And in the closed state, the valve stem and packing culvert are not in contact with the medium, ensuring that the valve stem and packing culvert are not damaged or leaked.
Advantages
Once the electric globe valve is in the open state, there is no contact between its valve seat and the valve disc sealing surface, so the mechanical wear of its sealing surface is small, because the valve seat and valve disc of most electric globe valves are relatively easy to repair. Or when replacing the sealing element, there is no need to remove the entire valve from the pipeline, which is very suitable for occasions where the valve and pipeline are welded together. The most obvious advantage is that during the opening and closing process, because the friction between the valve disc and the sealing surface of the valve body is smaller than that of the gate valve, it is wear-resistant. The opening height is generally only 1/4 of the valve seat channel diameter, so it is much smaller than a gate valve. Usually there is only one sealing surface on the valve body and valve disc, so the manufacturing process is relatively good and it is easy to maintain. The flow direction of the medium changes when passing through this type of valve, so the flow resistance of the electric globe valve is higher than that of other valves.
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