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Knowledge of globe valves

The overview of globe valves
The globe valve is the valve whose valve discs (valve clacks) are driven by valve stems, moving linearly along the axis of the valve seat (sealing surfaces) up and down. The globe valve is generally composed of the drive member (the handwheel), valve stem, valve body, valve bonnet, valve clack (the closing member) and packing device. The hand wheel is connected with the valve stem and the valve stem is used to drive the valve clack so that the valve clack can move along the direction of the axis of the valve seat up and down. In that way, the pipeline can be turned on or off.

The globe valve is widely used and is mainly used in high pressure and small diameter occasions. Generally, the biggest diameter of the globe valve is DN400 (NPS16). The globe valve with a larger diameter is only applied to special pipelines. For example, a large oxygen pipeline uses stainless steel globe valves with large diameters, because other valves are easily on fire caused by friction.

The working principle of globe valves
Generally, the valve stem of the globe valve rotates and moves up and down. The hand wheel is fixed on the top of the stem. When the handwheel is rotated clockwise, the stem thread rotates downwards. The sealing surface of the valve clack is in close contact with the sealing surface of the valve seat, and the glove valve will be closed. When the handwheel is rotated counterclockwise, the stem thread rotates upward. The sealing surface of the valve clack and the sealing surface of the valve seat will be separated from each other. The globe valve will be opened.

Advantages and disadvantages of globe valves
Advantages of globe valves
a. Compared with the gate valve, the globe valve has a simple structure. Usually, the globe valve only has one sealing surface on the valve body and valve clack. The globe valve has small sealing area and can save precious materials, resulting in low costs. Therefore, the manufacturing process of the globe valve is relatively good and the maintenance is easy.
b. The sealing surface of the globe valve is worn and scratched lightly, and the globe valve has good sealing performance. When the valve is opened or closed, there is no relative sliding between the valve clack and the sealing surface of the valve body (except for the conical sealing surface). Therefore, wear and scratches of the globe valve are not serious, which makes the globe valve have good sealing surface and long service life.
c. The opening height of the globe valve is small, and it is generally only 1/4 of the diameter of the valve seat channel. The globe valve has compact structure, which saves installation space.

Disadvantages of globe valves
a. The globe valve has longer structure.
b. The globe valve has large opening and closing torque. When the globe valve is closed, the force of the medium must be overcome, because the direction of movement of the valve clack is opposite to the direction of the medium pressure.
c. The globe valve has large flow resistance. The medium channel in the valve body is relatively tortuous, resulting in large flow resistance and power consumption. The pressure loss of the globe valve is particularly obvious, especially in the hydraulic device. The flow resistance of the globe valve is the largest among the various types of cut-off valves.
d. The direction of media flow is limited.
When the medium flows through the globe valve, it can only flow from bottom to top or from top to bottom at the seat channel. Therefore, the medium can only flow in a single direction and the flow direction can not be changed.
e. When the globe valve is closed, solid particles in the fluid medium may be trapped between the sealing surfaces.
f. The globe valve is not easily installed.
 
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