Check valve related introduction

In fluid delivery systems, check valves play a key role in ensuring system stability and safety. As a valve that can automatically prevent the reverse flow of fluid, it can effectively prevent the damage caused by the reverse flow of fluid to equipment and systems, and is widely used in many fields. An in-depth understanding of the working principle, type, application scenario, industry status and development trend of check valves is of important practical significance for relevant practitioners and users.
1.The working principle
The check valve relies on the fluid's own power to automatically open and close to prevent the reverse flow of the fluid. When the fluid flows along the forward direction, the pressure of the fluid will overcome the valve disc gravity and spring force and other resistance, push the valve disc open, so that the fluid passes smoothly; When the fluid tries to flow in reverse, the valve disc will tightly fit the seat under the combined action of its own gravity and reverse fluid pressure, cutting off the reverse channel of the fluid.
The swing check valve, for example, has a hinged mechanism, and the disc, like a door, rests freely on the surface of the tilted seat. Under the action of positive fluid pressure, the valve disc rotates around the hinge to open; When the fluid flows in reverse, the disc rotates around the hinge to close by its own gravity and reverse fluid pressure. The valve disc of the lift check valve is located on the seat sealing surface of the valve body, and the positive fluid pressure makes the valve disc lift from the seat sealing surface to realize fluid flow; When the medium backflows, the disc falls back to the seat under the action of gravity and reverse fluid pressure, preventing the fluid backflow.
2.The types are diverse, each has its own advantages
Classification by structure
Lift check valve: The disc slides along the vertical center line of the body. This type of check valve has high fluid resistance and is usually suitable for small diameter pipes. It can be subdivided into vertical and horizontal two. Vertical lift check valve, the medium inlet and outlet channel direction is the same as the seat channel direction, the flow resistance is relatively small; In the straight-through type lift check valve, the direction of the medium inlet and outlet channel is perpendicular to the direction of the seat channel.
Swing check valve: The disc rotates around the rotating shaft to open and close the valve. According to the different caliber of the valve, it can be divided into single valve, double valve and multi-valve. It has less resistance to fluid and is suitable for large diameter pipelines. In the low-pressure large-diameter pipeline, in order to reduce the hydraulic impact generated when the medium stops flowing or backflows, multiple valves are often arranged on the channel partition of the valve to form a multi-disc structure.
Butterfly check valve: The disc is disc shaped and rotates around the rotating shaft of the valve seat channel. Butterfly check valve structure is simple, the resistance to the fluid is small, but the tightness is relatively poor, generally used for the need for slow closing function of the occasion, such as the fire pump outlet, can avoid the water hammer and pump reversal.
Pipe type check valve: the valve disc slides along the center line of the valve body, small size, light weight, good processing ability, is one of the future development directions of the check valve, but its fluid resistance coefficient is slightly larger than the swing type check valve.
Pressure type check valve: The valve has the combined function of lifting type check valve and globe valve or Angle valve, often used as boiler feed water and steam cut-off valve.
Classification by material
Check valve materials are rich and varied, common cast iron, brass, stainless steel, carbon steel, forged steel and so on. Check valves of different materials are suitable for different working environments and media requirements. For example, cast iron check valves have low cost and are suitable for some occasions with low corrosion resistance requirements; The stainless steel check valve has good corrosion resistance and is suitable for pipelines conveying corrosive media.
Classification by function
In addition to the above common types, there are some check valves with special functions. The silent check valve can reduce the noise generated during the valve opening and closing process, the rubber flap check valve has a good sealing performance, and the double flap check valve further enhances the sealing effect to meet the special needs of the check valve in specific scenarios.
3.Widely used, indispensable
Industrial field
Chemical industry: In the chemical production process, many fluids have corrosive or high viscosity characteristics. The check valve prevents these fluids from backflowing, protecting the equipment and avoiding problems such as uncontrolled chemical reactions caused by fluid backflow.
Oil and gas industry: The medium transported in this industry usually has high temperature and high pressure characteristics. Check valves are used to prevent the flow of fluid in the pipeline system to ensure the safety and stability of the transport process.
Power industry: In the boiler feed water system, the check valve can prevent the phenomenon of water shock, ensure the stable operation of the system, and avoid damage to the equipment caused by water shock.
Water treatment system
Water supply system: Check valves prevent water hammering and protect pumps and pipes. When the pump stops running, the water backflow is prevented to avoid damage to the pump and ensure the normal operation of the water supply system.
Sewage treatment plant: prevent sewage backflow, avoid the spread of pollution, ensure the smooth progress of the sewage treatment process, and prevent the treated sewage from being polluted again.
Civil domain
Home water system: installed in the home water pipeline to prevent water backflow, protect household water safety, and avoid water quality pollution caused by water backflow.
Fire protection system: Ensure one-way flow of fire protection water to improve system reliability. In the event of a fire, ensure that the fire water can be smoothly transported to the fire fighting site to provide guarantee for the fire fighting work.