When the installation space is limited on the structure, attention should be paid 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 valve seat sealing surfaces 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 rear of the pipeline is large, which makes the sealing surface wear more seriously. The structure of the gate valve will be more complicated than that of the globe valve. From the perspective of appearance, the gate valve is taller than the globe valve and the globe valve is longer than the gate valve under the same diameter. In addition, gate valves are divided into open rods and dark rods. The shut-off valve does not. Working principle When the globe valve is opened and closed, it is of a rising valve stem type, that is to say, when the handwheel is turned, the handwheel will rotate and lift together with the valve stem. The gate valve is to rotate 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 require fully open or fully closed, and globe valves do not. Globe valves have specified inlet and outlet directions, while gate valves do not have requirements for inlet and outlet directions. In addition, the gate valve has only two states: fully open or fully closed, the gate opening and closing stroke 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 regulation. The gate valve can only be used for truncation and has no other functions. Performance difference The globe valve can be used for both cut-off and flow regulation. The fluid resistance of the globe valve is relatively large, and it is more 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 0, 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 installation and flow direction of the gate valve have the same effect in both directions. The installation does not require the direction of the inlet and outlet, and the medium can flow in both directions. The globe valve needs to be installed in strict 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 'three chemical processes' of valves in my country stipulate that the flow direction of the globe valve shall be from top to bottom. The globe valve is low in and high out, and it is obvious from the outside that the pipeline is not on the horizontal line of one phase. The gate valve flow channel is on a horizontal line. The stroke of the gate valve is larger than that of the globe valve. From the point of view of flow resistance, the flow resistance of the gate valve is small when it is fully opened, and the flow resistance of the load check valve
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 3-5 times that of gate valves. When opening and closing, it needs to be forced to close to achieve sealing. The valve core of the globe 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 of the main force, the globe valve that needs 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 the packing is not under pressure when the valve is closed, which can prolong the service life of the packing and can bear the pressure in the pipeline before the valve. Under the circumstance, the replacement of the packing is carried out; the disadvantage is that the driving torque of the valve is large, which is about 1 times that of the upper flow, 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 globe valves (below DN50), and the globe valves above DN200 use the method that the medium flows in from above. (The electric globe valve generally adopts the way of entering the medium from above.) The disadvantage of entering the medium from the top is just the opposite of the way of entering from the bottom. The sealing surface of the closed globe valve is a small trapezoidal side of the valve core (specifically depends on the shape of the valve core). Once the valve core falls off, it is equivalent to closing the valve (if the pressure difference is large, of course, it is not tightly closed, but the anti-reverse effect is not bad. ), the gate valve is sealed by the side of the valve core gate, the sealing effect is not as good as that of the globe valve, and the valve core falling off will not be equivalent to the valve closing like the globe valve.
Collectively, the effect of valve application on industrial society has been to eliminate types of industrial valves and drastically reduce the time long associated with types of industrial valves.
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