What is a check valve - explain the use and structural characteristics

Check valves, which can be misunderstood, play a vital role in piping systems. They are designed to flow in one direction and automatically prevent backflow when the fluid is reversed, ensuring stable operation of the piping system. Unlike other Valves, check valves open and close automatically without the need for external assistance, allowing them to continue to function even when the plant facility loses power or is manually operated.

Not only are these valves varied, but they are also used in a wide range of applications. They can be found in everything from sump Pump discharge lines in homes to desalination, chemicals, food and beverages in the industrial sector. They are capable of handling a wide range of media, including liquids, air, steam, and in some cases, even liquids containing particles or slurries. It can be used in a wide range of applications, from pump and compressor discharge pipes to loading racks and nitrogen purge lines.

However, despite the integral role that check valves play in piping systems, they are also often misunderstood. Many people think they don't work and may even avoid using them because of misconceptions. The purpose of this article is to help readers fully understand this important valve by in-depth discussion of the basics, working principles, type selection, installation and maintenance of check valves, so as to avoid unnecessary misunderstandings and losses.

Check valves are extremely sensitive to flow changes, and their opening and closing are primarily dependent on the pressure and flow rate in the line. As the fluid flows forward, the disc is pushed to open the valve; As the flow decreases or flows in the opposite direction, the disc begins to close the valve, a process that behaves differently depending on the design. The core function of a check valve is to prevent the fluid from backflowing. Its structure is relatively simple, usually containing only a few main components: valve body, valve seat, valve disc and valve cover. Depending on the design, components such as stems, hinge pins, disc arms, springs, balls, elastomers, and bearings may also be included.

It is important to note that the internal sealing of a check valve relies primarily on "reverse" line pressure rather than mechanical force. As a result, the allowable seat leakage rate is generally higher than that of valves used for on/off control. However, manufacturers perform rigorous seat and housing closure tests on check valves to ensure performance and quality through standards such as MSS SP-61 "Pressure Test for Steel Valves".

There are a number of factors that can affect seat leakage in check valves, including reverse pressure, media characteristics, and seat material. For example, metal and PTFE seat surfaces may allow for some leakage, while elastomers such as Buna-N and Viton provide a near-perfect bubble seal closure (zero leakage). Therefore, when selecting a check valve, it is necessary to fully consider the type of media and the operating conditions to ensure that the appropriate elastomer material is selected.