The valve is used as a starting and closing member and moves along the axis of the valve seat to realize the opening and closing action of the valve. The shut-off valve is mainly used to cut off the fluid, and can also be used to regulate the flow in the case where the regulation performance is not high. The shutoff valve is a type of valve commonly used on pipes. Common stop valve body flow channels are available in straight-through, direct-flow and right-angled versions (Figure 1). The straight-through stop valve (Fig. 2) has a large fluid resistance, and is called a spherical valve because the shape of the valve body is similar to a sphere. In order to reduce the fluid resistance, a DC type (Y type) shut-off valve and a right angle cut-off valve appear later. The direct current type is mostly used for fluids containing solid particles or high viscosity. Right angle type right angle pipe for high and medium pressure.
The sealing surface of the shut-off valve is mainly composed of a flat surface and a tapered surface. The width of the contact surface of the cone seal is smaller than that of the plane seal, the required sealing force is small, the sealing property is easy to ensure, and the opening and closing force is also much lower, and it is mostly used in high pressure applications. In order to reduce the opening and closing force, a high pressure balanced shut-off valve has been developed. It uses a pressure balanced valve flap. Fluid enters the upper part of the valve flap from the lower part of the valve flap through a small hole, which counteracts most of the axial force exerted by the fluid on the valve flap.
The main advantage of the stop valve is that the opening height is small (usually 1/4 of the diameter of the valve seat through hole), so the switch is relatively quick; during the opening and closing process, there is generally no relative sliding between the sealing surfaces, so it is not easy to wear and scratch; the valve flap and The valve seat is easy to maintain. The disadvantage is that the opening and closing force and the fluid resistance are large, so it cannot be made too much. Generally, the nominal diameter of the medium and low pressure shut-off valves is not more than 250 mm, and the high-pressure shut-off valve is not more than 150 mm.
The main disadvantages of the shut-off valve are: large fluid resistance, large force required to open and close; not suitable for media with particles, high viscosity, easy to coke; poor regulation performance.
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