Principle and use of check valve

Check Valve refers to the valve that automatically opens and closes the valve flap by relying on the flow of the medium itself to prevent the backflow of the medium, also known as check valve, one-way valve, reverse flow valve, and back pressure valve. The check valve is an automatic valve whose main function is to prevent the backflow of the medium, the reverse rotation of the pump and the driving motor, and the discharge of the container medium. 1. In order to prevent the backflow of the medium, check valves should be installed on the equipment, devices and pipelines; 2. The check valve is generally suitable for clean media, and should not be used for media containing solid particles and high viscosity; 3. Generally in the nominal Horizontal lift check valves should be used on horizontal pipes with a diameter of 50mm; 4. Straight lift check valves can only be installed on horizontal pipes; On the vertical pipeline at the pump inlet, and the medium flows from bottom to top; 6. The lifting type has better sealing performance and larger fluid resistance than the swing type. The horizontal type should be installed on the horizontal pipeline, and the vertical type should be installed on the vertical pipeline; 7. . The installation position of the swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines. If it is installed on a vertical pipeline, the flow direction of the medium should be from bottom to top; 8. Swing check valve It is not suitable to be made into a small-diameter valve, and it can be made into a very high working pressure. The nominal pressure can reach 42MPa, and the nominal diameter can also be large, and the maximum can reach more than 2000mm. It can be applied to any working medium and any working temperature range according to the different materials of the housing and seals. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196--800 ℃; 9. The swing check valve is suitable for low pressure and large diameter, and the installation occasion is limited; 10. The installation position of the butterfly check valve is not limited, and it can be Installed on horizontal pipelines, and can also be installed on vertical or inclined pipelines; Structural principle of check valve Swing check valve is almost unimpeded by fluid pressure when fully opened, so the pressure drop through the valve is relatively small. little. The disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the valve disc can rise and fall freely, the rest of the valve is like a globe valve. The fluid pressure lifts the valve disc from the sealing surface of the valve seat, and the backflow of the medium causes the valve disc to fall back to the valve seat and cut off the flow. According to the conditions of use, the disc can be of all-metal structure, or it can be in the form of rubber pads or rubber rings embedded on the disc holder. Like the globe valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow of the swing check valve is limited rare. 1. Swing check valve: The disc of the swing check valve is disc-shaped and rotates around the shaft of the valve seat channel. Because the channel in the valve is streamlined, the flow resistance is smaller than that of the lift check valve. It is suitable for large-diameter occasions with low flow rate and infrequent changes in flow, but it is not suitable for pulsating flow, and its sealing performance is not as good as that of lifting type. The swing check valve is divided into three types: single-lobe type, double-lobe type and multi-half type. These three types are mainly divided according to the diameter of the valve. 2. Lifting check valve: a check valve whose disc slides along the vertical centerline of the valve body. Lifting check valves can only be installed on horizontal pipelines. For high-pressure small-diameter check valves, the disc can be made of balls. . The valve body shape of the lift check valve is the same as that of the globe valve (it can be used in common with the globe valve), so its fluid resistance coefficient is larger. Its structure is similar to the globe valve, and the valve body and disc are the same as the globe valve. The upper part of the valve disc and the lower part of the valve cover are machined with guide sleeves. The valve disc guide can be freely lifted and lowered in the valve guide. When the medium flows downstream, the valve disc is opened by the thrust of the medium. It falls vertically on the valve seat to prevent the reverse flow of the medium. The direction of the medium inlet and outlet channels of the straight-through lift check valve is perpendicular to the direction of the valve seat channel; the vertical lift check valve has the same direction of the medium inlet and outlet channels as the valve seat channel, and its flow resistance is smaller than that of the straight-through type. 3. Disc check valve: a check valve in which the disc rotates around the pin in the valve seat. The disc check valve has a simple structure and can only be installed on the horizontal pipeline, and the sealing performance is poor. 4. Pipeline check valve: a valve in which the disc slides along the centerline of the valve body. Pipeline check valve is a new valve. It is small in size, light in weight and good in processing technology. It is one of the development directions of check valve. However, the fluid resistance coefficient is slightly larger than that of the swing check valve. 5. Compression check valve: This kind of valve is used as a valve for boiler feed water and steam cut-off. It has the comprehensive function of lift check valve and globe valve or angle valve. In addition, there are some check valves that are not suitable for pump outlet installation, such as bottom valve, spring type, Y type, etc.
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