Gate valve refers to a valve whose closing member (gate plate) moves in the vertical direction along the center line of the passage. Gate valves are mainly used for cutting off in pipelines.
The opening and closing part of the stop valve is a plug-shaped valve disc, the sealing surface is flat or conical, and the valve disc moves linearly along the center line of the fluid.
Is it different from a globe valve?
The answer is yes, what's the difference?
Imported gate valves and imported stop valves are commonly used products for imported valves, especially their caliber, pressure, temperature, and material range. The caliber can be DN10-1000, the temperature can be from -196 to 600°C, and the materials include cast iron, cast steel, and stainless steel. , duplex steel, low-temperature steel, alloy steel, etc., with a very wide range of uses. For example, VTON's different types of imported gate valves and imported stop valves can be used for almost all media including water, steam, gas, oil, etc.; However, there are still certain differences in the structural characteristics and selection of imported gate valves and imported globe valves. Let’s analyze the differences and uses of the two.
1. Structural differences
The length of the gate valve is shorter than that of the globe valve, and the height is higher than that of the globe valve. Pay attention to the height when installing the rising stem gate valve. This should be paid attention to when selecting when the installation space is limited. Where the installation space is limited, the imported stop valve is suitable; the gate valve can rely on the medium pressure to tightly seal with the sealing surface to achieve the effect of no leakage. When opening and closing, the sealing surfaces of the valve core and the valve seat are always in contact and grind 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, making the sealing surface wear more serious.
2. Differences in principle
The difference in principle between the stop valve and the gate valve is that the stop valve has a rising valve stem, and the handwheel rotates and rises along with the valve stem. The gate valve rotates with the handwheel and the valve stem moves upward. Therefore, the manual opening and closing time of imported gate valves is longer than that of imported stop valves. For example, VTON's DN300 gate valve needs to be turned several hundred times and takes several minutes to open manually. The flow rate is different, and the gate valve needs to be fully open or fully closed. The stop valve is not required. Globe valves have specified inlet and outlet directions; gate valves have no inlet and outlet direction requirements.
Explanation: The fluid-passing part of the gate valve is the same as the straight pipe, but there is a gate plate in the pipe. If the gate plate is lifted up, the door will be fully opened, while the fluid in the stop valve rotates in the valve. 180-degree bend, usually the fluid enters from one side of the valve and turns a 90-degree angle to flow upward after entering the valve. After flowing to the upper part of the valve body, it turns a 90-degree angle and flows out. When the fluid flows in the valve, it turns 90 degrees and flows out. A cover is added to the outlet of the upstream. When the cover is put on, the door closes. When the cover is opened, the valve opens. From flow upward:
The stop valve has a low inlet and a high outlet. From the outside, it is obvious that the pipeline is not on the same phase level. The gate valve flow path is on a horizontal line. The stroke of the gate valve is larger than that of the globe valve.
Explanation: From the perspective of flow resistance, the flow resistance of the gate valve is small when fully open, while 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 both directions. The flow resistance of ordinary stop valves is 3-5 times that of gate valves. When opening and closing, forced closing is required to achieve sealing. The valve core of the stop 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 main flow force, the stop valve that requires an actuator should pay attention to the torque control mechanism. Adjustment.
3. Differences in installation methods
1. The flow direction of the gate valve has the same effect from both sides.
2. 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 can be installed in the pipeline in front of the valve. Under pressure, replace the packing; the disadvantage is that the driving torque of the valve is large, about 1 times that of the flow from above, 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 (under DN50). Stop valves above DN200 all use the method of medium flowing in from above. (Electric stop valves generally use the method of medium entering from above.) The disadvantages of the method of medium entering from above are exactly opposite to the method of entering from below.
3. Differences in sealing surfaces
The sealing surface of the stop valve is a small trapezoidal side of the valve core (depending on the shape of the valve core). Once the valve core falls off, it is equivalent to the valve closing (if the pressure difference is large, of course it will not close tightly, but the anti-return effect is not bad). The gate valve is sealed by the side of the gate plate of the valve core. The sealing effect is not as good as that of the globe valve. The falling of the valve core will not be equivalent to the valve closing like the globe valve.
Temperature and pressure, soft and hard seal gate valve selection are mainly based on the process medium. Individual media contain solid particles or are abrasive or the temperature is higher than 200 degrees. It is best to choose a hard-sealed valve with a diameter larger than 50. If the pressure difference is large, the closing torque of the valve should also be considered. When the torque is large, a fixed hard-sealed gate valve should be selected.