The difference between gate valve and globe valve

1. Structurally
When the installation space is limited, attention should be paid to the selection of models. The gate valve can be tightly closed with the sealing surface by the pressure of the medium, so as to achieve the effect of no leakage. When opening and closing, the valve core and the sealing surface of the valve seat are always in contact with each other and rub against each other, so the sealing surface is easy to wear. When the gate valve is close to closing, the pressure difference between the front and rear of the pipeline is very large, which makes the sealing surface wear more serious.
The structure of the gate valve is more complicated than that of the globe valve. From the appearance point of view, under the same caliber, the gate valve is taller than the globe valve, and the globe valve is longer than the gate valve. In addition, gate valves are also divided into bright rods and dark rods. Globe valve no.
2. Working principle
When the globe valve is opened and closed, it is of the rising stem type, that is to say, when the handwheel is turned, the handwheel will rotate and lift along with the valve stem. The gate valve is to turn the handwheel to make the valve stem move up and down, and the position of the handwheel itself remains unchanged. Flow rates vary, gate valves are required to be fully open or fully closed, while globe valves are not. Globe valves have specified inlet and outlet directions; gate valves have no requirements for inlet and outlet directions.
In addition, the gate valve has only two states of fully open or fully closed, the opening and closing stroke of the gate plate is large, and the opening and closing time is long. The movement stroke of the valve plate of the globe valve is much smaller, and the valve plate of the globe valve can stop at a certain place during the movement for flow adjustment. The gate valve can only be used as a cut-off, and has no other functions.
3. Performance difference
The globe valve can be used both for cut-off and flow regulation. The fluid resistance of the stop valve is relatively large, and it is laborious to open and close, but because the distance between the valve plate and the sealing surface is short, the opening and closing stroke is short.
Because the gate valve can only be fully opened and fully closed, when it is fully opened, the medium flow resistance in the valve body channel is almost zero, so the opening and closing of the gate valve will be very labor-saving, but the distance between the gate and the sealing surface is long, and the opening and closing time is long .
4. Installation and flow direction
The effect of gate valve flow in both directions is the same, there is no requirement for the direction of inlet and outlet for installation, and the medium can flow in both directions. The globe valve needs to be installed strictly in accordance with the direction marked by the arrow on the valve body. There is also a clear regulation on the direction of the inlet and outlet of the globe valve. The flow direction of the globe valve in my country is stipulated by the "three modernizations" to be from top to bottom.
The cut-off valve is low in and high out, and it is obvious from the appearance that the pipeline is not on the first phase level. The flow channel of the gate valve is on a horizontal line. The stroke of the gate valve is larger than that of the globe valve.
From the perspective of flow resistance, the flow resistance of the gate valve is small when fully open, and the flow resistance of the load stop valve is large. The flow resistance coefficient of ordinary gate valve 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 3-5 times that of gate valves. When opening and closing, it needs to be closed by force to achieve sealing. The spool of the stop valve only contacts the sealing surface when it is completely closed, so the wear of the sealing surface is very small. Due to the large flow force, the stop valve that needs to be equipped with an actuator should pay attention to the torque control mechanism. Adjustment.
There are two ways to install the globe valve. One is that the medium can enter from the bottom of the valve core. The advantage is that when the valve is closed, the packing will not be under pressure, which can prolong the service life of the packing and allow the pipeline in front of the valve to bear pressure. Under the circumstances, the work of replacing the packing is carried out; the disadvantage is that the driving torque of the valve is relatively large, which is about 1 times that of the upper inflow, the axial force on the valve stem is large, and the valve stem is easy to bend.
Therefore, this method is generally only applicable to small-diameter globe valves (below DN50), and globe valves above DN200 all use the method of medium flowing in from above. (Electric globe valves generally adopt the method of medium entering from above.) The disadvantage of medium entering from above is just the opposite of that entering from below.
5. Seal
The sealing surface of the stop valve is a small trapezoidal side of the valve core (see the shape of the valve core for details). Once the valve core falls off, it is equivalent to the valve closing (if the pressure difference is large, of course it cannot be closed tightly, but the anti-return effect is not bad). The gate valve is sealed by the side of the gate plate of the valve core, the sealing effect is not as good as that of the globe valve, and the falling of the valve core will not be equivalent to the valve closing like the globe valve.