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April 08, 2020

Difference between globe valve and gate valve

The difference between the stop valve and the Gate Valve is that the working principle is different. The stop valve is of the rising stem type. The handwheel rotates and rises with the stem. Gate valve is a handwheel rotation, stem to do a rising motion. The flow rate is different. The gate valve is required to be fully open. The stop valve is not. The gate valve has no requirements for the direction of inlet and outlet, and the stop valve has specified inlet and outlet! Gate valve and stop valve are shut-off valves, which are the most common two kinds of valves. From the appearance, gate valve is shorter and higher than stop valve, especially rising stem valve needs higher height space. The sealing surface of gate valve has certain self sealing ability. Its valve core tightly contacts with the sealing surface of valve seat by the medium pressure, so that it is tight without leakage. The inclination of wedge gate valve is generally 3 ~ 6 degrees. When the valve core is forced to close excessively or the temperature changes greatly, it is easy to get stuck. Therefore, high temperature and high pressure wedge gate valves have taken certain measures to prevent the valve core from sticking in the structure. When the gate valve is opened and closed, the valve core and the sealing surface of the valve seat always contact and rub with each other, so the sealing surface is easy to wear. Especially when the valve is close to the closed state, the pressure difference between the front and back of the valve core is large, and the wearing of the sealing surface is more serious.

Features of stop valve and gate valve:

Compared with the stop valve, the main advantage of the gate valve is that the flow resistance is small. The flow resistance coefficient of the common gate valve is about 0.08 ~ 0.12, while the resistance coefficient of the common stop valve is about 3.5 ~ 4.5. The opening and closing force is small, and the medium can flow in two directions. The disadvantage is that the structure is complex, the height and size are large, and the sealing surface is easy to wear. The sealing surface of the stop valve must be closed by force to achieve sealing. Under the same caliber, working pressure and the same driving device, the driving torque of the stop valve is 2.5-3.5 times of that of the gate valve. This should be paid attention to when adjusting the torque control mechanism of Electric Valve. The sealing surface of the stop valve contacts each other only when it is completely closed. The relative slip between the valve core and the sealing surface is very small, so the wear of the sealing surface is very small. However, the wear of the sealing surface of the stop valve is mostly caused by the sundries in front of the valve core and the sealing surface, or the high-speed scouring of the medium caused by the untight closing state.

Installation features of stop valve and gate valve:

When the stop valve is installed, the medium can enter from the lower part of the valve core and from the upper part. The advantage of medium entering from the bottom of the valve core is that the packing is not under pressure when the valve is closed, which can extend the service life of the packing, and can replace the packing when the pipeline in front of the valve is under pressure. The disadvantage of medium entering from the lower part of the valve core is that the driving torque of the valve is larger, about 1.05-1.08 times of that of the upper part. The valve rod is subject to large axial force, and the valve rod is easy to bend. Therefore, the medium entry mode from below is generally only applicable to small caliber manual stop valve, with the force of medium acting on the valve core not more than 350kg when the valve is closed. The electric stop valve generally adopts the way of medium entering from above. The disadvantage of media entry from the top is just the opposite of that from the bottom. Compared with the gate valve, the stop valve has the advantages of simple structure, good sealing performance and convenient manufacturing and maintenance; the disadvantage is large liquid resistance and large opening and closing force. Gate valve and stop valve belong to the full open and full close type valve, which are used for cutting off or connecting medium and not suitable for regulating valve. The application range of stop valve and gate valve is determined by their characteristics. In the smaller channel, when it is required to have better shut-off sealing, the stop valve is often used; in the steam pipeline and large-diameter water supply pipeline, because the fluid resistance is generally small, the gate valve is used.

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