Gate valves are linear movable valves that use the valve disc to open and close or regulate flow in the pipeline. In general, the gate of valve gates can be divided into a wedge shape, parallel shape, V-shaped form, and so on. The wedge-shaped gate of gate valves generally has a wedge shape on both sides with high friction so it is not suitable for throttling. The parallel gate is smooth on both sides and has high friction so it cannot be throttled easily. The V-shaped gate of gate valves has smooth surfaces on both sides but does not reduce friction significantly when opening or closing the valve seat because there are still some contact points between the two surfaces that must be overcome before separating from each other. Gate valves are widely used in oil refining and chemical industry pipelines, especially suitable for high-temperature, high-pressure pipelines.
A complete gate valve consists of several parts such as a valve body, valve seat, valve stem, gate plate, valve cover, seal ring, etc. The specific gate valve structure diagram is as follows:
The working principle of the gate valve:
The gate valve can only be fully open or fully closed, and cannot be used as a valve to regulate the flow. Its working principle is the gate with the stem – up and down for linear motion, the stem has a trapezoidal thread, through the nut on the top of the valve and the guide groove on the valve body, to achieve the up and down movement of the stem, the stem drives the gate movement. The direction of movement of the gate is perpendicular to the direction of the pipeline fluid medium.
Gate valve opening: The fully opened state of the gate valve is not viewable when it is in operation, especially for the concealed stem gate valve. The open state of the open stem gate valve can be observed to determine the exposed stem position, and the concealed stem gate valve – is generally open until it is not moving as a sign of full open. However, considering the possibility of locking due to temperature changes, the gate valve is generally opened to the head.
Gate valve closing: gate valve can have two forms of self-sealing and forced sealing after closing, self-sealing means that the sealing surface can only rely on the medium pressure to seal. But most the gate valve or the use of forced sealing, that is, the gate valve gate closed, rely on external force to force the gate to the seat. Usually, the sealing performance of the gate valve is better than the butterfly valve.
Gate valves have the following advantages.
① Fluid resistance is small. The Gate valve body’s internal media channel is straight, the media flow through the gate valve does not change its flow direction, and therefore the fluid resistance is small.
②The length of the structure (the distance between the two ends connected to the pipe) is small. As the gate is disc-shaped, is placed vertically in the valve body, while the globe valve flap (also disc-shaped) is placed parallel to the valve body, and thus compared with the globe valve, its structure length is smaller. Such as PN16, DN150 globe valve, its structure length is 480mm, while the same parameters of the gate valve structure length are only 350mm.
③Opening and closing more labor-saving. When opening and closing the gate movement direction is perpendicular to the direction of media flow, and the direction of movement of the globe valve flap is usually closed with the seat in the opposite direction of media flow, and therefore must overcome the force of the medium. Therefore, compared with the shut-off valve, the gate valve opening and closing is more labor-saving.
④Media flow direction is not restricted. The medium can flow through the gate valve in any direction from both sides of the gate valve and can achieve the purpose of connection or cut off.
⑤Easy Installation. Gate valves can be installed quickly and easily because they do not require special tools or heavy lifting equipment for installation or maintenance purposes.⑥The structure shape is relatively simple, and the manufacturing process is good.
At the same time, the gate valve also has some disadvantages as follows.
①The sealing surface is prone to abrasion. When opening and closing the gate plate and the valve seat contact between the two sealing surfaces has relative sliding, under the action of the medium thrust easy to produce abrasion to destroy the sealing performance of the gate valve.
②More parts, more complex structure, manufacturing, and maintenance are more difficult, compared with the cost of the shut-off valve are higher.
③The shape size and opening height are larger, and the space required for installation is also larger.
④Gate valves do not provide positive shut-off, which can lead to overpressurization of downstream piping if there is a sudden loss of power to the actuating motor.
⑤ Gate valves are more likely to leak than other types of valves because they do not seal well when closed. This means that if you use this type of valve often, you will need to perform more maintenance on your system.
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