The Features and Performance of Butterfly Valve
Jan 18,2023Read More
Globe valves, gate valves, butterfly valves, check valves and ball valves are all indispensable control components in various piping systems. Each valve has a different appearance, structure and functional purpose. However, there are some similarities in the appearance of stop valves and gate valves. At the same time, they all have the break-in function in the pipeline. Therefore, people who do not have much contact with valves will confuse the two types of valves. In fact, if you observe carefully, globe valves and gate valves are quite different.
(1) The selection should be paid attention to when the installation space is limited. Due to medium pressure, gate valves can be tightly closed with the sealing surface to make sure there is no leakage. When opening and closing, the valve core and the seat sealing surface are always in contact and rub against each other, which results in the sealing surface is easy to wear. When gate valves almost close, the pressure difference between the front and rear of the pipeline is very large, which will make more serious wear and tear on the sealing surface.
(2) Gate valves have more complicated structures than globe valves. In the case of the same caliber, gate valves are taller but shorter than globe valves. In addition, gate valves can be divided into rising stems and non-rising stems. However, globe valves do not have this classification.
(1) The stems will rise when opening and closing globe valves. When turning handwheels, they will rotate and lift together with valve stems. However, for gate valves, it is needed to rotate handwheels to make the valve stem move up and down, and the positions of handwheels remain unchanged.
(2) They have different flow rates. Gate valves have to be fully opened or fully closed while globe valves are not required. Globe valves have assigned inlet and outlet direction while gate valves have no direction requirements.
(3) Gate valves only have fully opened and fully closed states. The larger the opening and closing stroke of the gate, the longer the opening and closing time. The movement stroke of the valve plate of globe valves is much smaller, and it can be stopped at a certain place during the movement for flow adjustment. However, gate valves can only be used for cutting off, and it has no other functions.
(1) Globe valves can be used for cut-off and flow adjustment. The fluid resistance of globe valves is relatively large, and it is more difficult to open and close. However, the distance between the valve plate and the sealing surface is short, so the opening and closing strokes are short.
(2) Since gate valves can only be fully opened and fully closed, the flow resistance of the medium in the valve body channel is almost zero. Therefore, the opening and closing of gate valves will be very labor-saving. However, the gate is far away from the sealing surface, and the opening and closing time is long.
(1) The effect of gate valves in both directions is the same. There is no requirement for the direction of the inlet and outlet for installation, and the medium can flow in both directions. Globe valves need to be installed strictly under the direction indicated by the arrow on the valve.
(2) Globe valves are low in and high out, they have obvious pipes that are not on the same horizontal line. Flow paths of gate valves are on horizontal lines. Strokes of gate valves are larger than that of globe valves.
(3) In terms of flow resistances, when fully opened, gate valves have small flow resistances while globe valves have large flow resistances. The flow resistance coefficient of normal gate valves is about 0.08~0.12, and they have a small opening and closing force, and the medium can flow in two directions. The flow resistance of normal globe valves is 3-5 times that of gate valves. When opening and closing, it is necessary to force closing to achieve the sealing effect. Valve cores of globe valves only touch sealing surfaces when they are completely closed, so sealing surfaces have small wear and tear. Due to the large flow of the main force, it is needed to pay attention to the adjustment of the torque control mechanism of actuators of globe valves.
(3) There are two installation methods of globe valves. One of the methods 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. Also, the packing can be replaced when the pipe 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 that of the upper flow. The axial force on the valve stem is large, and the valve stem is easy to bend. Therefore, the method is generally only applicable to small-diameter globe valves (below DN50). For globe valves above DN200, the method that the medium enters from above should be chosen. The disadvantage of the method the medium enters from above is the opposite of the method the medium enters from below.
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