Structurally:
The length of the gate valve is shorter than the globe valve, and the height is higher than the stop valve. Pay attention to the height when installing the rising stem gate valve. This should be paid attention to when the installation space is limited. The gate valve can be tightly closed with the sealing surface depending on the medium pressure, so as to achieve the effect of no leakage. When the valve core and the sealing surface of the valve seat are always in contact and rub with each other when opening and closing, 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, which makes the sealing surface wear more seriously.
In principle:
The difference between the globe valve and the gate valve in principle is that the stop valve is of the rising stem type, and the handwheel rotates and rises together with the stem. Gate valve is a handwheel rotation, stem to do the rising movement. The flow rate is different. The gate valve is required to be fully open or fully closed, while the stop valve is not required. The stop valve has specified inlet and outlet directions; the gate valve has no requirements for inlet and outlet directions.
Explanation: the flow passage part of the gate valve is the same as that of the straight pipe, but a ram is set in the pipe. If the ram is lifted, the door will be fully opened, and the stop valve fluid will turn 180 degrees in the valve. Generally, the fluid enters from one side of the valve and turns 90 degrees upward after entering the valve, and then turns 90 degrees out after flowing to the upper part of the valve body, just like the fluid Add a cover at the outlet of the upward flow of the valve, and the door of the cover will be closed. Open the cover and the valve will be opened.
From flow direction:
The cut-off valve is low inlet and high outlet. From the appearance, it is obvious that the pipeline is not on the same phase horizontal line. The gate valve flow path is on a horizontal line. The stroke of gate valve is larger than that of stop valve.
Explanation: from the perspective of flow resistance, when fully open, the flow resistance of gate valve is small and that of load check valve is large. 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 common stop valve is 3-5 times that of gate valve. When the valve is opened and closed, it needs to be forced to close to achieve the sealing. The valve element of the stop valve contacts the sealing surface only when it is completely closed, so the wear of the sealing surface is very small. Because the main flow force is large, the stop valve with actuator should pay attention to the adjustment of the torque control mechanism.
From the installation:
- The flow direction of gate valve is the same from both sides.
- 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 the packing can be replaced when the pipeline in front of the valve is under pressure. The disadvantage is that the driving torque of the valve is large, which is about 1 times of the upper flow. The axial force of the valve stem is large, and the valve is subject to large axial force The rod bends easily. Therefore, this method is generally only applicable to small caliber stop valves (below DN50), and stop valves above DN200 adopt the way of medium flowing in from above. (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.
From the sealing surface:
The sealing surface of the stop valve is a small trapezoid side of the valve core (see the shape of the valve core specifically). Once the valve core falls off, it is equivalent to the valve closing (if the pressure difference is large, of course, it is not tight, but the check effect is good). The gate valve is sealed by the side of the valve core ram. If the sealing effect is not as good as the stop valve, the valve core falling off will not be equivalent to the valve closing as the stop valve.