The check valve refers to a valve that automatically opens and closes the valve flap by means of the flow of the medium itself, and is used to prevent the back flow of the medium, which is also called a check valve, a check valve, a reverse flow valve, and a back pressure valve. The check valve is an automatic valve whose main function is to prevent backflow of the medium, prevent the pump and drive motor from reversing, and discharge the container medium. The check valve can also be used to supply a line in which the pressure may rise to an auxiliary system that exceeds the system pressure. The check valve can be mainly divided into a swing type check valve (rotation according to the center of gravity) and a lift check valve (moving along the axis). Screw Air Compressor,Small Screw Air Compressor,Small Rotary Screw Air Compressor,Screw Type Air Compressor Hangzhou Zhongju air separation equipment manufacturing Co., Ltd , https://www.hzzjkfzz.com
The function of this type of valve is to only allow the medium to flow in one direction and prevent the direction from flowing. Usually, the valve is automatically operated, and the valve flap is opened by the fluid pressure flowing in one direction; when the fluid flows in the opposite direction, the fluid pressure and the self-reclosing valve flap of the valve disc act on the valve seat to cut off the flow.
Among them, the check valve belongs to this type of valve, which includes a swing check valve and a lift check valve. The swing check valve has a hinge mechanism and a door-like flap that rests freely against the inclined seat surface. In order to ensure that the valve flap can reach the proper position of the valve seat surface each time, the valve flap is designed in the hinge mechanism, so that the valve flap has enough swinging space and the valve flap is truly and comprehensively in contact with the valve seat. The discs can all be made of metal, or they can be inlaid with leather, rubber, or synthetic coverings depending on the performance requirements. In the fully open condition of the swing check valve, the fluid pressure is almost unimpeded, so the pressure drop across the valve is relatively small. The valve flap of the lift check valve is located on the valve seat sealing surface of the valve body. In addition to the valve flap being free to lift and lower, the valve is like a shut-off valve. The fluid pressure causes the valve flap to lift from the valve seat sealing surface. The return of the medium causes the valve flap to fall back to the valve seat and shut off the flow. Depending on the conditions of use, the flap may be of an all-metal construction or may be in the form of a rubber or rubber ring on the valve disc holder. Like the shut-off valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow rate of the swing check valve is limited. Very few.
The check valve can be divided according to its structure and installation method:
1. Swing-type check valve: The valve flap of the swing-type check valve is in the shape of a disk, and rotates around the rotating shaft of the valve seat passage. Because the valve passage is streamlined, the flow resistance is higher than that of the lift check valve. Small, suitable for large diameter applications where low flow rates and flow are not constantly changing, but not suitable for pulsating flow, and its sealing performance is not as good as lifting type. The swing-type check valve is divided into three types: single-valve, double-valve and multi-half. These three forms are mainly divided according to the valve diameter. The purpose is to prevent the hydraulic shock from being weakened when the medium stops flowing or reverses.
Second, the lift check valve: the check valve sliding along the vertical centerline of the valve body, the lift check valve can only be installed on the horizontal pipe, the valve can be used on the high pressure small diameter check valve . The shape of the lift check valve is the same as that of the shut-off valve (common to the shut-off valve), so its fluid resistance coefficient is large. Its structure is similar to the stop valve, the valve body and the valve flap are the same as the shut-off valve. The upper part of the valve flap and the lower part of the valve cover are machined with a guide sleeve, and the valve guide can be easily lifted and lowered in the valve guide guide. When the medium is downstream, the valve flap is opened by the medium thrust. When the medium stops flowing, the valve flap is self-retained. The drooping falls on the valve seat to prevent the medium from flowing back. The direction of the inlet and outlet passages of the straight-type lifting check valve is perpendicular to the direction of the valve seat passage; the vertical lift check valve has the same direction of the medium inlet and outlet passages as the valve seat passage, and its flow resistance is smaller than that of the straight-through type.
Third, the disc type check valve: a check valve that rotates around the pin shaft in the valve seat. The disc type check valve has a simple structure and can only be installed on a horizontal pipe, and the sealing property is poor.
4. Pipeline check valve: A valve whose valve slides along the center line of the valve body. Pipeline check valve is a new type of valve. It is small in size, light in weight and good in processability. It is one of the development directions of check valves. However, the fluid resistance coefficient is slightly larger than the swing check valve.
V. Press-type check valve: This valve is used as a boiler feed water and steam shut-off valve. It has a comprehensive function of a lift check valve and a shut-off valve or an angle valve.
In addition, there are some check valves that are not suitable for pump outlet installation, such as bottom valves, spring type, Y type and other check valves.