Globe valve, gate valve, butterfly valve, check valve and ball valve are all indispensable control parts in various pipeline systems. Each kind of valve is different in appearance, structure and even function. But globe valve and gate valve are similar in appearance, and both of them have the function of cutting off in the pipeline. So there will be many friends who have little contact with the valve may confuse globe valve with gate valve. In fact, if you carefully observe it, there is a big between the globe valve and the gate valve. This article will introduce the difference between globe valve and gate valve.
Structural difference between gate valve and globe valve
In the case of limited installation space, attention shall be paid to the selection. 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. If the valve core is in contact with the sealing surface of the valve seat and there is the friction when opening and closing, the sealing surface is easy to wear. When the gate valve will be closed, the pressure difference between the front and back of the pipeline is large, which makes the sealing surface wear more seriously. The structure of gate valve will be more complex than globe valve. From the appearance, under the same caliber, gate valve is higher than globe valve, and globe valve is longer than gate valve. In addition, gate valves are divided into open stem and concealed stem. Globe valve cannot be divided.
When the globe valve is opened and closed, it is rising stem type, which means, turning the hand wheel will rotate and lift along with the stem. The gate valve rotates the hand wheel so that the stem move up and down, and the position of the hand wheel remains unchanged. The flow rate is different. The gate valve is required to be fully open or fully closed, while the globe valve is not required. The globe valve has specified inlet and outlet directions; the gate valve has no requirements for inlet and outlet directions. In addition, the gate valve only has two states: full open or full close. The stroke of gate opening and closing is very 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 be stopped at a certain place during the movement for flow regulation. The gate valve can only be used for truncation without other functions.
Performance difference between gate valve and globe valve
Globe valve can be used for cut-off and flow regulation. The flow resistance of the globe valve is relatively large, and it takes time to open and close. However, the distance between the valve plate and the sealing surface is short, so the opening and closing stroke is short.
Installation and flow direction difference between gate valve and globe valve
In terms of flow direction of gate valve, the effect is the same in both directions. There is no requirement for the direction of inlet and outlet for installation, and the medium can flow in two directions. The globe valve should be installed in strict accordance with the direction indicated by the arrow of the valve body. There is a clear regulation on the direction of the inlet and outlet of the globe valve. According to the "serialization, universalization and standardization" of China's valves, the flow direction of the globe valve should be from top to bottom.
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 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 globe valve. The flow resistance of common globe valve is 3-5 times that of gate valve. The valve element of the globe valve contacts the sealing surface only when it is completely closed, so the wear of the sealing surface is very small. The main flow force is large, the globe valve of actuator is needed, so the adjustment of torque control mechanism should be paid attention to.
There are two methods to install the globe valve: one method is that the medium can enter from the bottom of the valve core. The utility model has the advantages that the packing is not under pressure when the valve is closed, the service life of the packing can be prolonged, 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 on the valve rod is large, and the valve rod is easy to bend.
Therefore, this method is generally only applicable to small caliber globe valves (below DN50), and globe valves above DN200 adopt the way of medium flowing in from above. (electric globe valve generally adopts the way that medium enters from above.) The disadvantage of media entry from the top is opposite of that from the bottom.
The sealing surface of the globe valve is a small trapezoid side of the valve core (it depends on 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, it will not be closed 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 globe valve, the falling off of the valve core will not be equivalent to the valve closing as the globe valve.