Definition

Check valve refers to a valve that automatically opens and closes the valve flaps by relying on the flow of the medium itself to prevent backflow of the medium. It is also known as a check valve, check valve, reverse flow valve, and back pressure valve.

Check valve function

The check valve belongs to an automatic valve. Its main functions are to prevent backflow of the medium, prevent the pump and drive motor from reversing, and release the medium in the container. The check valve can also be used to replenish the auxiliary system where the pressure may rise above the system pressure.

Classification of check valves

Check valve can be divided according to its structure and installation method:

1. Swing check valve

The valve flap of the swing check valve is disc-shaped and rotates around the rotation axis 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 low flow rates and flow. Large-diameter occasions that change frequently, but are not suitable for pulsating flow, and its sealing performance is not as good as the lifting type. There are three types of swing check valves: single-petal, double-petal, and multi-half. These three types are mainly divided by the valve caliber. The purpose is to prevent the medium from flowing or backflow and weaken the hydraulic impact.

2. Lifting check valve

The check valve of the valve flap sliding along the vertical center line of the valve body, the lift check valve can only be installed on the horizontal pipeline, and the valve flap can be a ball on the high-pressure small-diameter check valve. The valve body shape of the lift check valve is the same as that of the cut-off valve (it can be used with the cut-off valve), so its fluid resistance coefficient is large. 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 flap and the lower part of the valve cover are processed with guide sleeves. The valve flap guide can be freely raised and lowered in the valve seat guide. When the medium flows downstream, the valve flap opens by the medium thrust. When the medium stops flowing, the valve flap depends on It lands on the valve seat and prevents the medium from flowing backwards. The direction of the media inlet and outlet channels of the straight-through lifting check valve is perpendicular to the direction of the valve seat channel; the vertical lifting check valve has the same medium inlet and outlet channel direction as the valve seat channel, and its flow resistance is smaller than that of the straight-through type.

3. Disc check valve

Check valve with flap rotating around a pin in the valve seat. The disc type check valve has a simple structure and can only be installed on horizontal pipelines with poor sealing.

4. Pipeline check valve

The valve slides along the centerline of the valve body. Pipeline check valve is a new type of valve. It has small volume, light weight and good processing technology. It is one of the development directions of check valve. But the fluid resistance coefficient is slightly larger than the swing check valve.

5. Compression check valve

This valve is used as a valve for boiler feed water and steam cut-off. It has a comprehensive function of a lift check valve and a globe valve or an angle valve.