Check valve refers to a valve whose opening and closing piece is a circular disc and ACTS by its own weight and pressure of medium to stop the backflow of medium. It is a kind of automatic valve, also known as reverse check valve, one-way valve, backflow valve or isolation valve. Disc movement is divided into lifting and swing. The lift-off check valve is similar to the globe valve and lacks only the stem to drive the disc. The medium flows in from the inlet (lower side) and out from the outlet (upper side). When the inlet pressure is greater than the combined weight of the disc and its flow resistance, the valve is opened. Conversely, the valve is closed when the medium is backflow. The swing check valve has an oblique disc that rotates about a shaft, and works in a similar way to a lift check. Check valves are often used as bottom valves in pumping units to prevent backflow of water. Stop valve and globe valve combined use, can play a safe isolation role. Disadvantages are high resistance and poor sealing when closed.

Installation method

Swing check valve: the disc of swing check valve is like a disc, rotating around the axis of seat passage, because the valve inner passage is streamline, flow resistance is smaller than the lift check valve, suitable for low flow rate and flow do not change the large aperture occasions, but should not be used for pulsating flow, its sealing performance is not as good as the lift. There are three types of swing check valves: single valve type, double valve type and half valve type. These three types are mainly divided according to the valve diameter. The purpose of these three types is to prevent the medium from stopping the flow or reversing the flow to weaken the hydraulic impact.

2. Lift-off check valve: the valve disc slides along the vertical center line of the valve body. The lift-off check valve can only be installed on the horizontal pipe. The valve body of the lift-check valve is the same as the globe valve (can be used with the globe valve), so it has a higher fluid resistance coefficient. Its structure is similar to the globe valve, the body and disc are the same as the globe valve. The upper part of the disc and the lower part of the cover are machined with guide sleeve. The disc can freely rise and fall within the valve pot guide. When the medium is flowing along, the disc is opened by medium thrust. Straight up and down check valve medium inlet and outlet channel direction perpendicular to seat channel direction; Vertical lifting check valve, its medium inlet and outlet channel direction and seat channel direction, its flow resistance is relatively small.

Disc check: disc check valve rotating around the pin in the seat. Disc check valve is simple in structure and can only be installed in horizontal pipe.

Pipeline check valves: valves that slide the disc along the center line of the body. Pipeline check valve is a new valve, small size, light weight, processing technology is good, is one of the development direction of check valve. But the fluid resistance coefficient is slightly larger than the swing check valve.

Compression check: this valve is used for boiler water supply and steam cut-off. It has the integrated function of lifting check valve and globe valve or Angle valve.

In addition, there are some non-applicable pump outlet check valves, such as bottom valve, spring, Y type, and so on.

Matters needing attention

1. Do not allow check valves to bear weight in the piping system. Large check valves should be independently supported to protect them from pressure generated by the piping system.
2. Note that the flow direction of medium should be consistent with the arrow direction of valve body.
3. The lift-down vertical disc check valve shall be installed on the vertical pipe.
4. The lift-down horizontal disc check valve shall be installed on the horizontal pipe.