Stop valve, gate valve, butterfly valve, check valve and ball valve are indispensable control components in various pipeline systems. Each valve is different in appearance, structure and even functional use. However, the globe valve and gate valve have some similarities in appearance, and both have the function of cutting off in the pipeline. Therefore, many friends who have little contact with the valve will confuse the two. In fact, if you observe carefully, the difference between stop valve and gate valve is quite big.
Valve structure:
When the installation space is limited, attention should be paid to the selection. The gate valve can be tightly closed with the sealing surface by medium pressure, so as to achieve the effect of no leakage. 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. When the gate valve is close to closing, the pressure difference between the front and rear of the pipeline is large, making the wear of the sealing surface more serious.
The structure of the gate valve will be more complex than the stop valve. From the appearance, in the case of the same diameter, the gate valve is higher than the stop valve, and the stop valve is longer than the gate valve. In addition, the gate valve can be divided into exposed rod and concealed rod. The stop valve is not.
working principle:
When the stop valve is opened and closed, it is a rising stem type, that is, rotate the handwheel, and the handwheel will rotate and rise and fall with the valve stem. The gate valve rotates the hand wheel to make the valve stem rise and fall, and the position of the hand wheel itself remains unchanged. The flow 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 inlet and outlet direction requirements. In addition, the gate valve is only fully open or fully closed. The opening and closing stroke of the gate valve is large and the opening and closing time is long. The movement stroke of the valve plate of the stop valve is much smaller, and the valve plate of the stop valve can stop at a certain place during movement for flow regulation. The gate valve can only be used for cut-off without other functions.
Performance differences:
The stop valve can be used for both cut-off and flow regulation. The fluid resistance of the stop valve is relatively large and the opening and closing is laborious, but the opening and closing stroke is short because the distance between the valve plate and the sealing surface 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 is very labor-saving, but the gate is far from the sealing surface and the opening and closing time is long.
Installation and flow direction:
The effect of gate valve flow direction is the same in both directions. There is no requirement for inlet and outlet direction during installation, and the medium can flow in both directions. The stop valve needs to be installed in strict accordance with the direction marked by the arrow of the valve body. There is also a written provision on the inlet and outlet direction of the stop valve. The "three modernizations" of valves in China stipulates that the flow direction of the stop valve shall be from top to bottom.
The stop valve is low in and high out. 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 the gate valve is larger than that of the stop valve.
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 the common cut-off valve is 3-5 times that of the gate valve (official account: Pump housekeeper). When opening and closing, the valve core of the stop valve contacts the sealing surface only 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 with actuator should pay attention to the adjustment of torque control mechanism. There are two ways to install the stop valve. One is that the medium can enter from below 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 replace the packing 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 twice the flow from above. The axial force on the valve rod is large, and the valve rod is easy to bend. Therefore, this method is generally only applicable to small-diameter stop valves (below DN50). Stop valves above DN200 use the method of medium flowing from above. (the electric stop valve usually adopts the way that the medium enters from above.) The disadvantage of media entering from above is just the opposite to that from below.
Sealing method:
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 closing the valve (if the pressure difference is large, it can not be closed tightly, but the check effect is good). The gate valve is sealed by the side of the valve core gate. The sealing effect is not as good as that of the stop valve, and the valve core falling off will not be equivalent to closing the valve as the stop valve.
