Globe valves, gate valves, butterfly valves, check valves, ball valves, etc. are all indispensable control components in various pipeline systems. Each valve is different in appearance, structure and even functional use. However, the globe valve and the gate valve have some similarities in appearance, and both have the function of cutting off in the pipeline, so many friends who have little contact with valves will confuse the two. In fact, if you observe carefully, the difference between the globe valve and the gate valve is quite large.

1 Structural

When the installation space is limited, you should pay attention to the selection. The gate valve can be tightly closed with the sealing surface by the medium pressure, so as to achieve the effect of no leakage. When opening and closing, the valve core and the valve seat sealing surface are always in contact 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 back of the pipeline is very large, which makes the sealing surface wear more seriously. The structure of the gate valve will be more complicated than the globe valve. From the appearance point of view, under the same caliber, the gate valve is higher than the globe valve, and the globe valve is longer than the gate valve. In addition, the gate valve is also divided into a rising stem and a concealed stem. The globe valve does not have.

2  Working principle

When the stop valve is opened and closed, it is a rising valve stem type, that is, when the handwheel is turned, the handwheel will rotate and rise and fall with the valve stem. The gate valve turns the handwheel to make the valve stem rise and fall, and the position of the handwheel itself remains unchanged. The flow rate is different. The gate valve requires full opening or full closing, while the stop valve does not. The stop valve has specified inlet and outlet directions; the gate valve has no inlet and outlet direction requirements.In addition, the gate valve has only two states: full opening or full closing. The gate opening and closing stroke is large and the opening and closing time is long. The valve plate movement stroke of the stop valve is much smaller, and the valve plate of the stop valve can stop at a certain place during the movement for flow regulation. The gate valve can only be used for cutting off and has no other functions.

3 Performance difference

The stop valve can be used for both cutting off and flow regulation. The fluid resistance of the stop valve is relatively large, and it is more laborious to open and close, but 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 opened and fully closed, when it is fully opened, the medium flow resistance in the valve body channel is almost 0, so the gate valve will be very labor-saving to open and close, but the gate is far away from the sealing surface, and the opening and closing time is long.

4 Installation and flow direction

The gate valve has the same effect in both directions, and there is no requirement for the inlet and outlet directions during installation, and the medium can flow in both directions. The stop valve needs to be installed strictly in the direction of the arrow mark on the valve body. There is also a clear regulation on the inlet and outlet directions of the stop valve. my country’s valve “three-in-one” stipulates that the flow direction of the stop valve is always from top to bottom.

The stop valve is low inlet and high outlet, and from the outside it is obvious that the pipeline is not on the same horizontal line. The gate valve flow channel is on the same horizontal line. The stroke of the gate valve is larger than that of the stop valve.

From the perspective of flow resistance, the gate valve has a small flow resistance when fully opened, and the check valve has a large flow resistance. The flow resistance coefficient of an 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 stop valves is 3-5 times that of gate valves. When opening and closing, forced closure is required to achieve sealing. The valve core of the stop valve contacts the sealing surface only when it is completely closed, so the wear of the sealing surface is very small. Since the main flow force is large, the stop valve that needs an actuator should pay attention to the adjustment of the torque control mechanism.

There are two ways to install the stop valve. One is that the medium can enter from the bottom of the valve core. The advantage is that the packing is not under pressure when the valve is closed, which can extend the service life of the packing, and the packing can be replaced when the pipeline in front of the valve is under pressure; the disadvantage is that the driving torque of the valve is large, which is about 1 times that of the flow from the top, and the axial force on the valve stem is large, and the valve stem is easy to bend. Therefore, this method is generally only suitable for small-diameter stop valves (below DN50), and stop valves above DN200 use the method of medium flowing in from the top. (Electric stop valves generally use the method of medium entering from the top.) The disadvantage of the method of medium entering from the top is exactly the opposite of the method of entering from the bottom.