Views:13 Author:Site Editor Publish Time: 2020-08-17 Origin:Site
All valves are designed to stop, allow or throttle the flow of process fluid. Gate valve-an original valve structure-is very suitable for switching, mainly liquid, applications. The working principle of the gate valve is to lift a rectangular or circular gate plate from the fluid channel. When the valve is fully open, the inner diameter of the gate valve is full, which means that nothing obstructs the flow, because the gate valve and the pipe diameter have the same opening. This inner diameter also determines the valve diameter. One advantage of this full hole design is that the friction loss is very low, saving energy and reducing the total cost of ownership.This article is about how the gate value works.
Four primary design for gate value
The stem and bonnet of gate value
The working principle of gate value
(1) The flat gate valve is composed of a single gate valve unit, which moves up and down between the two valve seat rings, and is mainly used to transport crude oil.
(2) The expansion gate valve includes two units-the gate and the segment gate, and the flat gate has only one unit. When the valve is fully opened or completely closed, the gate valve and the valve segment unit will close to each other during operation, thereby affecting the mechanical seal.
(3) The wedge gate valve uses a metal-to-metal sealed conical gate valve. Compared with the flat gate valve or expansion gate valve, the wedge gate valve is not removable, because when the valve is opened, the bottom of the valve body will leave a gap. These valves themselves have no through holes; on the contrary, when the valve is opened, the gate is retracted into the valve body, saving a high space.
(4) The knife gate valves are used to cut very thick fluids and dry solids. The design of this valve makes it inherently self-cleaning, because when the knife passes through the seat ring and skirt, each stroke will remove the abrasive. Compared with other gate valve types, the gate plate of this type of gate valve is relatively thin, and is guided into place by the water-type valve body sandwiching the gate plate.
The gate valve may adopt a rising stem structure or a non-rising stem structure. The rising stem is directly connected to the gate valve, providing a visual indicator of the valve position. The non-rising valve stem is usually screwed into the upper part of the gate, and a pointer is screwed into the top of the gate to indicate the position. The non-rising valve stem design is ideal for applications with limited vertical space, such as in wells that do not require scraping or pigging.
Gate valves generally have four types of bonnets that provide a closing function to prevent fluid leakage from the valve. The screw-in bonnet is a simple and durable sealing device that uses pressure sealing. For applications requiring frequent maintenance or inspection, the union bonnet can be easily connected to the valve body. Bolted bonnets are usually used for valves with higher pressure.
The valve stem trapezoidal thread of the rising valve stem gate valve is located outside the valve body and on the upper part of the valve stem. The valve stem rotates the valve stem nut to synchronously raise and lower the valve plate to realize the opening and closing of the valve. Therefore, it is easy to identify the open and closed state of the valve to avoid misoperation. Stem nuts are widely used because they are externally lubricated and open and close visually. However, in harsh environments, the exposed threads in the valve stem are easily damaged and corroded, which may even affect operation. The disadvantage is that the valve has a large height after opening, and usually a stroke is performed on the basis of the original valve height, so a large operating space is required.
That’s all about the working principle of gate valves, do you get it?