These valves, such as globe valves, gate valves, butterfly valves, check valves and ball valves are indispensable control components in various piping systems. Each valve differs in appearance, structure and even functional use. However, the shut-off valve and the gate valve have some similarities in shape, and at the same time have the function of cutting off in the pipeline, so there will be many friends who do not have much contact with the valve to confuse the two. In fact, if you look closely, the difference between the globe valve and the gate valve is quite large.
If the installation space is limited, you should pay attention to the selection. The gate valve can be tightly closed by the medium pressure and tightly closed to achieve a non-leakage effect. When opening and closing, the sealing surface of the valve core and the valve seat always contact and rub against each other, so the sealing surface is easy to wear, and when the gate valve is close to close, the pressure difference between the front and the rear of the pipeline is large, and the sealing surface wear is more serious. The effect of the gate valve flowing in both directions is the same. There is no requirement for the direction of the inlet and outlet, and the medium can flow in both directions. The shut-off valve needs to be installed in strict accordance with the direction marked by the arrow of the valve body. There is also a clear provision for the direction of the inlet and outlet of the shut-off valve. The flow direction of the shut-off valve specified by the “three-way” of the valve in China is always from top to bottom.
The shut-off valve is low in and out, and there are obvious pipes from the outside that are not on a horizontal line. The gate valve flow path is on a horizontal line. The stroke of the gate valve is larger than that of the shut-off valve.
From the point of view of flow resistance, the flow resistance of the gate valve is small at full opening, and the flow resistance of the carrier valve is large. The flow resistance coefficient of the 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 normal stop valve flow resistance is 3-5 times that of the gate valve (public number: pump housekeeper). When opening and closing, it is necessary to close the seal to achieve the seal. The spool of the shut-off valve only touches the sealing surface when it is completely closed, so the wear of the sealing surface is very small. Due to the large flow main force, the shut-off valve of the actuator should be paid attention to the adjustment of torque control mechanism.
There are two ways to install the shut-off 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, the life of the packing can be extended, and the pipe can be pressurized in front of the valve. In the case of the replacement of the packing; the disadvantage is that the driving torque of the valve is large, about 1 time the upper flow, 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-diameter globe valves (below DN50), and the shut-off valves above DN200 use the medium to flow in from above. (The electric shut-off valve is generally a medium that enters from above.) The disadvantage of the medium entering the way from the top is exactly the opposite of the way of entering below.
The structure of the gate valve is more complicated than the shut-off valve. From the aspect of the shape, the gate valve is higher than the shut-off valve in the same caliber, and the shut-off valve is longer than the gate valve. In addition, the gate valve has the distinction between a bright rod and a dark rod. The shutoff valve does not.
When the shut-off valve is opened and closed, it is lifted stem type, that is to say, the hand wheel is rotated, and the hand wheel rotates and lifts together with the valve stem. The gate valve is a rotating hand wheel, so that the valve stem can be lifted and moved, and the position of the hand wheel itself is unchanged. Flow rates vary; gate valves require full or full shutoff, while shut-off valves are not required. The shut-off valve has the specified inlet and outlet directions; the gate valve has no import and export direction requirements.
In addition, the gate valve has only two states of full opening or full closing, the stroke of the shutter opening and closing is large, and the opening and closing time is long. The valve plate movement stroke of the shut-off valve is much smaller, and the valve plate of the shut-off valve can be stopped at a certain position during the movement for flow regulation. The gate valve can only be used for truncation and has no other functions. The shut-off valve can be used for both cut-off and flow regulation. The fluid resistance of the shut-off valve is relatively large, and it is laborious to open and close. However, since 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 open and fully closed, when it is fully open, the medium flow resistance in the valve body passage is almost zero, so the opening and closing of the gate valve will be very labor-saving, but the gate is far away from the sealing surface, and the opening and closing time is long. .
The shut-off valve can be used for both cut-off and flow regulation. The fluid resistance of the shut-off valve is relatively large, and it is laborious to open and close. However, since 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 open and fully closed, when it is fully open, the medium flow resistance in the valve body passage is almost zero, so the opening and closing of the gate valve will be very labor-saving, but the gate is far away from the sealing surface, and the opening and closing time is long.
The sealing surface of the shut-off valve is a small trapezoidal side of the valve core (specifically, the shape of the valve core). Once the valve core is detached, it is equivalent to the valve closing (if the pressure difference is large, of course, the sealing is not strict, but the anti-reverse effect is not bad), The gate valve is sealed by the side of the valve core, and the sealing effect is not as good as that of the shut-off valve. The valve core does not fall off like the shut-off valve.