Many valves are now essential control components in all kinds of piping systems, such as globe valves,
gate valves, butterfly valves, check valves and ball valves. Each valve is different in appearance, construction and even function and usage.
However, globe valves and gate valves have some similarities in appearance. At the same time, they have the function of doing truncation in the pipeline. Many people who are not familiar with the valves will be confused. In fact, if you look closely, globe valves and gate valves are quite different.
The differences between globe valves and gate valves are as follows.
1. The structure
The selection should be paid attention to when the installation space is limited. The gate valve can rely on the medium pressure and sealing surface to close tightly so as to achieve the effect of leakage. When opening and closing, the sealing surface of the valve core and seat always contact and rub against each other. Therefore, the sealing surface is easy to wear. When the gate valve is close to closing, the pressure difference between front and rear of the pipeline is large, which makes the sealing surface wear more serious.
The structure of gate valves will be more complex than that of the globe valve. From the appearance of the same caliber, the gate valve is higher than the globe valve. The globe valve is longer than the gate valve. In addition, the gate valve has an open rod and dark rod points. The globe valve does not have rods.
2. The working principle
When the globe valve opens and closes, it is the rise of the stem. The hand wheel will follow the stem to do rotation and up and down motion. The gate valve is to turn the handwheel, so that the valve stem to do lifting movement. The handwheel position is unchanged. Gate valves require to fully open or fully close, while the globe valves do not need to do that. The globe valve has provisions of the import and export direction. The gate valve has no inlet and outlet direction requirements.
In addition, the gate valve can only be fully open or fully closed in two states. The gate opening and closing stroke is very large. The plate motion stroke of the globe valve is much smaller. The plate of the globe valve can be stopped in a certain place when it moves to do flow regulation. The gate valve can only be used for truncation without other functions.
Perfomance
The globe valve can be used for both truncation and flow regulation. The fluid resistance of the globe valve is relatively large. It is more laborious to open and close because the valve plate is short from the sealing surface. The opening and closing stroke is short.
Because the gate valve can only be fully open and fully closed. When it is fully opened, the medium flow resistance in the valve body channel is almost 0. Therefore, the opening and closing of the gate valve will be very labor-saving. However, the gate is far from the sealing surface. The opening and closing time is long.
3. Installation and flow direction
The flow direction effect of gate valves is the same in both directions. The installation has no import and export direction requirements. The media can be two-way flow. Globe valves need to be installed strictly in accordance with the direction indicated by the arrow of the valve body. There is also a clear provision on the inlet and outlet direction of globe valves.
The globe valve is low into high. It is obvious the pipeline is not a phase level line from the outside. The runner of gate valves is in a horizontal line. The travel of gate valves is larger than that of globe valves.
From the point of view of flow resistance, when we fully open gate valves, the flow resistance is small and the load flow resistance of check valves is large. The flow resistance coefficient of ordinary gate valves is about 0.08~0.12. The opening and closing force is small, and the medium can flow in two directions. The flow resistance of ordinary globe valves is three to five times more than that of gate valves. The valve core of the globe valve only touches the sealing surface when it is completely closed, so the wear of the sealing surface is very small. There are two ways to install the globe valve. One is that the medium can enter from below the school. The advantage is that when the valve is closed, the disc is not under pressure, which can prolong the service life of the disc and can be replaced in the case of pressure in the pipe before the valve. The disadvantage is that the driving torque of the valve is larger, which is about one time the flow into the top. The axial force of the valve stem is large, and the valve stem is easy to bend. Therefore, this method is generally only applicable to small-caliber globe valves (DN50 or below) and the globe valve of DN200 or the way of medium flowing in from the top is chosen. (The electric globe valve is generally used from the top of the medium into the way.) The disadvantage of the medium coming in from above is the opposite of the medium coming in from below.
4. The seal
The cut-off valve sealing surface of valve cores is a small trapezoidal profile (see the shape of the valve core). If the valve core falls off, the valve is nearly closed (if the pressure difference is big, the check inverse effect is good). The gate valve is on the side of the heart gate to seal. The sealing effect is better than that of cut-off valves. The loss of valve cores is not like that, which is like the closed globe valves.
