The Misunderstood of Check Valves Among The Industrial Valves

Check valves are probably the most misunderstood industrial valves ever invented. Generally, misunderstood in their function and importance, when you mention check valves, the responses range from “they just don't work”to “never use them.”

Like other industrial valves, check valves are used with a variety of media: liquids, air, other gases, steam, condensate, and in some cases liquids with particulate or slurries. Applications include pump and compressor discharge, header lines, vacuum breakers, non-code pressure relief, steam lines, condensate lines, chemical feed pumps, cooling towers, loading racks, nitrogen purge lines, boilers, HVAC systems, utilities, pressure pumps, sump pumps, wash-down stations and injection lines.

Check valves are flow sensitive and rely on the line pressure and flow to open and close. The internal disc allows flow to pass forward, which opens the valve. The disc begins closing the valve as forward flow decreases or is reversed, depending on the design. The function or purpose of a check valve is to prevent reverse flow. Construction is normally simple with only a few components such as the body, seat, disc and cover. Depending on the design, there may be other items such as a stem, hinge pin, disc arm, spring, ball, elastomers and bearings.

Internal sealing of the check valve disc and seat relies on “reverse” line pressure as opposed to the mechanical force used for on/off control valves. Because of this, allowable seat leakage rates are greater for check valves than with on/off control valves. MSS SP-61 “Pressure Testing of Steel Valves,” published by the Manufacturers Standardization Society, is one standard used by manufacturers to perform seat and shell closure tests for check valves (as well as other valves). Factors affecting check valve seat leakage include reverse pressure, media, and what the seat material is made of (such as metal or an elastomer). Metal and PTFE seating surfaces generally will allow some leakage while elastomers such as Buna-N and Viton provide bubble-tight shutoff (zero leakage).

Because of this, elastomers should be considered for air/gas media and low-pressure sealing. Important considerations when using elastomers for such valves are service temperature and compatibility of the elastomer with the media.

Various types of check valves are available. The popular types are Swing Check,Piston/Poppet Check, Flange Insert Check,Center Guided Check,Center guided check,Ball Checks. All these can be used for clean media. As with other types of valves, specialty check valves can be found for unique applications. While no one type of valve is good for all applications, each has its advantages.

Industrial Valves can be bought at affordable price rates from the valve manufacturers.