What is a check valve?
Definition of check valve：
The check valve is the opening and closing member (valve flap) with the force of the medium, automatically stopping the backflow of the medium valve.
Check valve, once called “check valve” or “check valve”, is mainly used for the one-way flow of media on the pipeline to prevent the backflow of media in the pipeline. Check valve belongs to the automatic valve category, its opening and closing action is dependent on the medium itself to drive the energy.
The basic function of the check valve is to protect machinery and equipment in the piping system by preventing the backflow of the medium. This is particularly important for pumps and compressors. Because backflow can cause damage to the internal components of the equipment, causing unnecessary stops, and in serious cases, even the entire plant stops operation.
Generally speaking, the check valve does not require manual operation, it is automatically operated by the media backflow. But in some special conditions, its one-way flow characteristics had to be changed. To achieve the above purpose, the check valve can be equipped with a device that locks the closing member in the open state, or the method of removing the closing member can be used.
The latter method requires that the check valve be disassembled, the shut-off piece removed, and the valve reinstalled.
This media pattern is necessary to prevent backflow, maintain system pressure after a pump stop, allow reciprocating pumps and compressors to operate properly, and prevent rotor pumps and compressors from driving equipment in reverse.
Check valves can also be used on lines that provide make-up for auxiliary systems where the pressure may rise above the main system pressure.
How Check Valves Work？
Check valves allow fluid to flow in a specific direction and prevent it from flowing back or in the opposite direction. The ideal check valve should begin to close when the pressure in the line drops and the kinetic energy of the fluid slows. When the direction of fluid flow is reversed, the check valve should close completely.
Operating characteristics of check valves：
Check valves are characterized by large load changes, small opening and closing frequency, once in the closed or open state, the use cycle will be long, and does not require the rotation of moving parts. However, once there is a switching requirement, the action must be flexible, this requirement is more demanding than the common mechanical movement. As the check valve in most practical use, qualitatively identified for rapid closure, and in the moment of closing the check valve, the medium is reverse flow, with the closure of the valve flap, the medium from the maximum backflow speed quickly to zero, while the pressure is rapidly rising, that is, may have a destructive effect on the pipeline system, “water hammer” phenomenon.
For multiple pumps in parallel with the use of a high-pressure piping system, the check valve water hammer problem is more prominent. Water hammer is a pressure wave of transient flow in the pressure pipeline, it is due to changes in fluid flow rate in the pressure pipeline caused by the pressure rise or fall of the hydraulic shock phenomenon. The physical principle of its generation is the incompressibility of the liquid, fluid motion inertia, and pipe elasticity of the combined results. In order to prevent the hidden danger of water hammer in the pipeline, over the years, people in the design of check valves, the use some new structures, in order to ensure the use of check valve performance at the same time, the impact of water hammer to minimize the progress made.