Stop valves, gate valves, butterfly valves, check valves and ball valves are now indispensable control components in various pipeline systems. Each valve is different in appearance, structure and even function. However, stop valves and gate valves have some similarities in appearance, and both have the function of cutting off in the pipeline. Therefore, many friends who have little contact with valves will confuse the two. In fact, if you observe carefully, the difference between stop valve and gate valve is quite big.

Structurally

When the installation space is limited, attention should be paid to the following when selecting the type:

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 sealing surface of the valve seat are always in contact and friction with 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 large, making the wear of the sealing surface more serious.

The structure of the gate valve will be more complex than the stop valve. From the appearance, under the same diameter, the gate valve is higher than the stop valve, and the stop valve is longer than the gate valve. In addition, the gate valve can be divided into open and closed rods. There is no stop valve.

working principle

When the stop valve is opened and closed, it is a rising stem type, that is to say, when the hand wheel is turned, the hand wheel will rotate and rise and fall along with the valve stem. The gate valve rotates the hand wheel to make the valve stem move up and down, and the position of the hand wheel itself remains unchanged.

The flow varies. The gate valve is required to be fully open or closed, while the stop valve is not required. Stop valves have specified inlet and outlet directions, and gate valves have no requirements for inlet and outlet directions.

In addition, the gate valve has only two states: fully open or fully closed. The opening and closing stroke of the ram is large and the opening and closing time is long. The movement stroke of the valve plate 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 without other functions.

Performance differences

The stop valve can be used for both cut-off and flow regulation. The fluid resistance of the stop valve is relatively large, and it is difficult 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 0, so the opening and closing of the gate valve is very labor-saving, but the distance between the gate valve and the sealing surface is far, and the opening and closing time is long.

Installation and flow direction

The effect of the gate valve is the same in both directions. There is no requirement for the direction of inlet and outlet in the installation, and the medium can flow in both directions. The stop valve needs to be installed in strict accordance with the direction marked by the arrow of the valve body. There is also a written regulation on the inlet and outlet direction of the stop valve. The "three modernizations" of valves in China stipulates that the flow direction of the stop valve is from top to bottom.

The stop valve is low in and high out. From the appearance, it is obvious that the pipeline is not on the same phase horizontal line. The flow passage of the gate valve is on a horizontal line. The stroke of gate valve is larger than that of stop valve.

From the perspective of flow resistance, the flow resistance of gate valve is small and that of load check valve is large when it is fully opened. 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 stop valve is 3-5 times that of gate valve. When opening and closing, it needs to be closed forcibly 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. Due to the large flow main force, the stop valve with actuator should pay attention to the adjustment of 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 prolong the service life of the packing, and can replace the packing when the pipe in front of the valve is under pressure; The disadvantage is that the driving torque of the valve is large, which is about twice the upper flow. The axial force on the valve rod is large, and the valve rod is easy to bend.

Therefore, this method is generally only applicable to small-diameter stop valves (below DN50), and stop valves above DN200 use the method of medium flowing from above. (the electric stop valve usually adopts the way that the medium enters from above.) The disadvantage of media entering from above is just the opposite to that from below.