Check valve, also known as one-way valve or check valve, belongs to the automatic valve category, and its function is to prevent the backflow of the medium in the pipeline. The bottom valve used for pump suction is also a type of check valve. The disc of the check valve is opened under the action of fluid pressure, and the fluid flows from the inlet to the outlet. When the inlet pressure is lower than the outlet, the valve flap is automatically closed under the action of fluid pressure difference, gravity and other factors to prevent the fluid from flowing back.
The classification of check valves can be divided into different types according to material, function and structure. The following will introduce the types of check valves from these three aspects.
1. Classification by material
1) Cast iron check valve
2) Brass check valve
3) Stainless steel check valve
2. Classification by function
1) Silent check valve
Ball check valve is also called sewage check valve. The valve body adopts a full channel structure, which has the advantages of large flow and low resistance. The ball is used as the valve disc, which is suitable for industrial and domestic sewage pipe networks with high viscosity and suspended solids.
3. Classification by structure
3) Butterfly check valve
The structure of the lift check valve is generally similar to that of the globe valve. The valve disc moves up and down along the line in the channel, and the action is reliable, but the fluid resistance is large, and it is suitable for occasions with small diameters. Lift check valve is divided into two types: horizontal type and vertical type. Straight-through lift check valves can generally only be installed on horizontal pipelines, while vertical check valves and bottom valves are generally installed on vertical pipelines, and the medium flows from bottom to top.
The disc of the swing check valve rotates around the axis of rotation. Its fluid resistance is generally smaller than that of the lift check valve, and it is suitable for occasions with larger diameters. According to the number of discs, swing check valve can be divided into three types: single disc swing type, double disc swing type and multi disc swing type. Single flap swing check valve is generally suitable for medium diameter occasions. If a single flap swing check valve is used for large-diameter pipelines, in order to reduce the water hammer pressure, it is best to use a slow-closing check valve that can reduce the water hammer pressure. Double flap swing check valve is suitable for large and medium diameter pipelines. Wafer double flap swing check valve is small in structure and light in weight, and is a kind of check valve with rapid development. Multi-lobe swing check valve is suitable for large diameter pipelines.
The installation position of the swing 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 dump pipeline.
The structure of the butterfly check valve is similar to that of a butterfly valve. Its structure is simple, the flow resistance is small, and the water hammer pressure is also small.
The connection methods of check valve include clip connection, flange connection, threaded connection, butt welding/socket welding connection, etc. The applicable temperature range is -196℃~540℃. Valve body materials are WCB, CF8 (304), CF3 (304L), CF8M (316), CF3M (316L). Choose different materials for different media. Check valve can be applied to water, steam, oil, nitric acid, acetic acid, oxidizing medium, urea and other media.
When installing the check valve, special attention should be paid to the flow direction of the medium, and the normal flow direction of the medium should be consistent with the direction of the arrow indicated on the valve body, otherwise the normal flow of the medium will be cut off. The bottom valve should be installed at the bottom end of the suction line of the pump.
When the check valve is closed, water hammer pressure will be generated in the pipeline, which will cause damage to the valve, pipeline or equipment in severe cases, especially for large-mouth pipelines or high-pressure pipelines, please pay close attention.
Original Source: https://www.dongshengvalve.com/news/types-of-check-valves/
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