How Does the Check Valve Work?

Jun. 10, 2020 

Check valves are probably the most misunderstood valves in history. If you mention check valves to most factory personnel, the typical response is "they don't work." In fact, these people are likely to have removed internal components or reinstalled system piping to avoid check valves.

The check valve allows one-way flow and automatically prevents back flow (reverse flow) when the fluid in the pipeline reverses flow. They are one of the few automatic valves that do not require auxiliary opening and closing. Unlike other valves, even if the power plant facility loses air, electricity, or someone who may manually circulate the valve, the valve can continue to work.

Check valves are everywhere, including at home. If you have a sewage pump in the basement, there may be a check valve on the pump discharge line. Outside the home, they can be found in almost every industry where pumps are located.

Like other valves, check valves can also be used for various media: liquids, air, other gases, steam, condensate, and in some cases, liquids with fine particles or mud. Applications include pump and compressor discharge, headers, vacuum circuit breakers, steam lines, condensation lines, chemical feed pumps, cooling towers, loading racks, nitrogen purge lines, boilers, HVAC systems, utilities, pressure pumps, sewage Pumps, flushing stations, and spray lines.

How they operate

Check valves are sensitive to flow and rely on pipeline fluid to open and close. The internal flap allows fluid to flow forward, thereby opening the valve. The disc starts to close the valve because the forward flow decreases or reverses, depending on the design. The structure is usually very simple, with only a few parts, such as the valve body, valve seat, valve flap, and valve cover. Depending on the design, there may be other items such as valve stems, hinge pins, clapper arms, springs, balls, elastomers, and bearings.

The internal sealing of the check valve disc and valve seat depends on the fluid back pressure, not the mechanical force used to open and close the valve. Therefore, the allowable valve seat leakage rate of the check valve is greater than that of the on-off valve. Metal sealing surfaces usually allow some leakage, while elastomers, such as nitrile rubber and fluoroelastomer, provide airtight closure (zero leakage). Therefore, elastomers should be considered for chemically compatible air/gas media and low-pressure seals.

The above information is provided by the check valve supplier.