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Check valve is also known as reverse flow valve, check valve, back pressure valve and one-way valve. This type of valve belongs to an automatic valve and is automatically opened and closed by the force generated by the flow of the medium itself in the pipeline. The industrial check valves are used in the pipeline system, and their main function is to prevent the backflow of the medium, prevent the random reversal of the pump and its drive motor, and discharge the medium in the container. The check valve can also be used on the line supplying the auxiliary system.
The check valve is installed on the pipeline and becomes one of the fluid components of the complete pipeline. The opening and closing process of the valve flap is affected by the transient flow state of the system in which it is located. In turn, the closing characteristics of the valve flap have an effect on the fluid flow state. The working characteristics of the check valve are that the load changes greatly, and the opening and closing frequency is small. Once it enters the closed or open state, the service cycle is very long, and it does not require the movement of moving parts. Since the check valve is qualitatively determined for fast closing in most practical use, and the medium flows in a direction at the moment when the check valve is closed. With the closing of the valve disc, the medium backflow speed rapidly drops to zero, and the pressure rises rapidly, which produces a "water hammer" phenomenon that may damage the pipeline system. For a high-pressure pipeline system where multiple pumps are used in parallel, the water hammer problem of the check valve is more prominent. Over the years, people have adopted some new structures and new materials in the design of the check valve to minimize the impact force of the water hammer while ensuring the performance of the check valve.
The purpose of using an industrial check valve is to prevent the backflow of the medium. Generally, a check valve should be installed at the outlet of the pump. In addition, a check valve should also be installed at the outlet of the compressor. In short, a check valve should be installed on the equipment, device or pipeline in order to prevent the reverse flow of the medium. Generally, vertical lift check valves produced by professional vertical check valve manufacturers are used on horizontal pipelines with a nominal diameter of 50mm. Straight-through lift check valve can be installed on both horizontal and vertical pipelines. The bottom valve is generally only installed on the vertical pipeline of the pump inlet, and the medium flows from bottom to top.
(1) Swing type check valve
Swing type check valve can withstand high working pressures. It can be applied to any working medium and any working temperature range according to the different materials of the shell and seal. The installation position of the swing type check valve is not limited, it is usually installed on the horizontal pipeline, but it can also be installed on the vertical pipeline or the inclined pipeline.
(2) Butterfly type check valve
Butterfly check valve is suitable for low pressure and large diameter, and the installation situation is limited. The working pressure of the butterfly check valve cannot be very high, so the butterfly check valve can be made into a wafer type, which is generally installed between the two flanges of the pipeline and adopts the form of wafer connection. The installation position of butterfly check valve is not limited, it can be installed on horizontal pipeline, vertical pipeline or inclined pipeline.
(3) Diaphragm type check valve
Diaphragm type check valve is suitable for pipelines that are prone to water hammer. The diaphragm can well eliminate the water hammer caused by the reverse flow of the medium. They are generally used in low-pressure and normal-temperature pipelines, and are especially suitable for tap water pipelines since the working temperature and operating pressure of diaphragm check valves are limited by the diaphragm material. Diaphragm type check valve has been widely used in recent years due to its excellent waterproof performance, relatively simple structure and low manufacturing cost.
(4) Ball type check valve
The ball type check valve has good sealing performance, reliable operation and good water hammer resistance because the seal is a sphere covered with rubber. It can be made into a large diameter because the seal can be a single ball, and can be made into multiple balls. However, its seal is a hollow sphere covered with rubber, which is not suitable for high-pressure pipelines, but only for medium and low-pressure pipelines. It can also be used in pipelines with general corrosive media since the shell material of the ball check valve can be made of stainless steel, and the hollow sphere of the seal can be covered with PTFE engineering plastic.
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