1. What is an axial flow check valve?
- The axial flow check valve is similar to the lift check valve in structure. The valve core moves along the axis of the valve body to realize the opening and closing action of the valve. However, the streamlined design of the inner cavity of the valve body and the guide cover makes the fluid present a laminar flow state on the flow surface, avoiding the occurrence of turbulence. It not only reduces energy loss, but also ensures the stability of the fluid flow state, thereby avoiding cavitation and noise.
- The axial flow check valve is mainly composed of valve body, valve seat, valve disc, spring, guide rod, guide sleeve and guide cover. The inlet medium pressure pushes the valve disc to open, and the surface of the inlet side of the valve disc is arc-shaped. After opening, it is combined with the guide cover to form a spindle, which reduces the flow resistance. After the pump is stopped, the inlet pressure gradually decreases. Under the action of the spring, the valve disc closes to prevent backflow. After the outlet pressure gradually increases, the valve disc is pressed tightly to ensure the sealing of the check valve. The valve disc is stable, shock-absorbing, silencing, and water hammer reduction when closing.
- The structural forms include disc type, ring disc type, and sleeve type. The disc type is a more commonly used structural form. When the diameter is larger, it is better to use a double-sided guide rod. The minimum opening pressure of the axial flow check valve (when in a horizontal state) should not be greater than 2kPa (0.002MPa)
2. What is a swing check valve
- The valve disc of the swing check valve rotates around the pin shaft outside the valve seat, so that the valve disc can be opened and closed flexibly. The back of the valve disc is fixedly installed on one end of the rocker by connecting the screw and nut, and the other end of the rocker is hingedly installed on the inner wall bracket of the valve body, ensuring the stability and reliability of the valve disc.
- When the inlet medium pressure acts on the valve disc, it will rotate open, allowing the medium to pass smoothly. After the pump is stopped, the outlet medium pressure and the valve disc's own weight will cause the valve disc to close to prevent the medium from flowing back. After the valve disc is opened, there is no resistance from other parts in the valve, which is equivalent to a pipeline, so the flow resistance is small.
- According to the different disc structures, swing check valves are divided into single-disc swing check valves, double-disc swing check valves and multi-disc swing check valves.
3. What is the difference between a swing check valve and an axial flow check valve:
- The valve structure is different. The valve core of the axial flow check valve is a lifting structure, the inner cavity of the valve body adopts a Venturi structure, the valve core and the guide cover are combined into a spindle, and the fluid flows through in a laminar state, avoiding the pressure loss caused by turbulence. The opening and closing of the swing check valve is achieved by the rotation of the valve disc.
- Different flow resistance. There is a reset spring on the valve core of the axial flow check valve, and the valve core and the guide cover are located in the middle of the valve body. The flow resistance is larger. After the swing check valve disc is opened, there are no other parts in the flow channel, and the flow resistance is smaller.
- Different applicable working conditions. The pressure of axial check valve can reach PN16-PN250, and the diameter is DN25-DN2000. The medium is water, oil, natural gas, etc., and the temperature is ≤100℃. The pressure of swing check valve is PN16-ON420, DN15-DN600, and the operating temperature is ≤538℃. The medium is water, oil, chemical industry, natural gas, etc. Swing check valve is more widely used. But the diameter of axial check valve can be made larger.
- The closing speed of the valve core is different. The closing speed of the axial check valve is faster, and the valve core is spring-loaded. When the inlet medium pressure is lower than the spring thrust, the valve core can be closed, and the switching noise is small. The swing check valve relies on the weight of the valve disc and the backflow of the medium to push the valve disc to reset, and closes slowly.
- The slow closing structure is different. The slow closing structure of the axial check valve is inside the valve body. The slow closing process is achieved by adding a piston and a slow closing cylinder to the guide rod. The swing check valve has a slow closing structure inside and outside the valve body. The slow closing function is achieved by adding a slow closing cylinder to the outside of the valve plate pin or by having a slow closing cylinder inside.
