Valve Standards

For consistency amongst manufacturers, valves are designed to meet established standards. These standards are set for valve performance, design, materials, and functionality. This article aims to cover the organizations responsible for establishing standards in valve manufacturing, along with common valve ratings and testing procedures.

Valve Standards Organizations

Valve standards are created by private entities that develop best practices in the use of valves and piping systems. Some of the The four organizations that are most referred to when discussing valve standards are the American Petroleum Institute (API), Manufacturers Standardization Society (MSS), International Organization for Standardization (ISO), and American Society of Mechanical Engineers (ASME), and The American Society for Testing and Materials (ASTM).

American Petroleum Institute (API)

The American Petroleum Institute is a the only national trade association that represents all aspects of America’s oil and natural gas industry. The API began around the first World War when the US government and the Oil & Gas industry worked together for the war effort. API is the go-to organization for valve testing for industrial valves in North America.

Manufacturers Standardization Society (MSS)

The Manufacturers Standardization Society is a non-profit technical association. MSS of the Valve and Fittings standards Iindustry developed international codes and standards for valves, valve actuators, and pipe fittings, pipe hangers, pipe supports flanges, and associated seals. along with many other components in piping systems.

MSS is approved accredited by the ANSI (American National Standards Institute), which subjects MSS standards to review.


The International Organization for Standardization is a the largest developer of voluntary international standards. The ISO is tied to 165 166 national standards entities worldwide. International standards are important because they are critical for international trade by as they ensureing consistency. This comes in the form of instituting product quality, safety, and efficiency to protect consumers.


The American Society of Mechanical Engineers was founded in 1880 the late 19th century as a society for engineers to hold discussions to improve upon their concerns in rising technology and industrialization. This standards organization has been improving the safety of equipments used in manufacturing and construction, particularly boilers and pressure vessels for r years. Regarding piping and valves, ASME has two series that cover the topics. Those two series are the B16.X and the B31.X series.

B.16 is a series of standards that provides dimensional standards and pressure/temperature ratings for pipe fittings and valves.

B31 series establishes best practices and allowable materials standards for a variety of piping systems.


The American Society for Testing and Materials was founded near the beginning of the 20th century. Today the ASTM sets voluntaryis as one of the largest standards organizations in the world, with 30,000 members. ASTM’s scope ranges from nanotechnology to skiing. There are six sets of standards: testing, specifications, classification, standard practice, guides, and terminology.

ASTM primarily sets classification, practice, and testing standards for valves. These standards can relate to valves, the materials that are used, or even the applications.

Allowable Operating Pressure

Allowable operating pressure refers to the safe operating pressure and temperature of a valve in a system either using ASME Class rating system, WOG or WSP ratings. MSS SP25 established a marking system to identify valves allowable operating pressure ratings quickly. There are three ratings for allowable operating pressure – , ASME class ratings, WOG ratings, and WSP ratings. This blog will cover ASME and WOG ratings more in depth. WSP stands for Working Steam Pressure. WSP ratings set standards for allowable working pressure at 100% saturated steam.

ASME Ratings

ASME ratings use definitions of classes to determine ratings. The term “class” can easily be mistaken for the term “pound,” an old term from WOG and WSP rating systems. The distinction between class and pound is crucial because these are two separate rating systems. ASME Classes are detailed in ASME B16.34.

For example, a 150 Pound WOG rating is designed for a maximum operating pressure of 150 PSI at 100° Fahrenheit. Compared to an ASME Class 150 in Group 2.1 (Stainless steels) materials the rating would be 275 PSI would be designed for a maximum operating pressure of 275 PSI at 100° Fahrenheit.

Common ASME class ratings for steel valves are 150, 300, 600, 900, 1500, 2500, and 4500. Ratings are based on Material Group. See example below for Group 1.1 (Carbon Steels).

[table] “WORKING PRESSURE by classes, psig”
[Footnote] ASME Class ratings chart

WOG Ratings

WOG stands for Wwater, Ooil and Ggas. WOG ratings define the maximum allowable operating pressure at +100° Fahrenheit. Valves that do not meet ASME class rating requirements will provide a chart of WOG ratings. These charts will show the allowable operating temperature and pressure for the valve. The valve materials ultimately influence the valve’s maximum operating temperature.

WOG ratings are typical for Ball Valves, Resilient-Seat Butterfly Valves, Diaphragm Valves, Polymer-Lined Valves, PVC Valves, and other soft-seated valves.

WOG ratings are shown on stamped metal tags that are fixed to the valve. These tags will display the valve manufacturer, the model number, and the pressure rating.

Control Valve Standards

Fluid Control Institute (FCI) is an association that assist buyers in understanding the fluid (liquid or gas) control and conditioning equipment. FCI currently comprisescovers control valves, instruments, pipeline strainers, regulators, secondary pressure drainers, solenoid valves, and steam traps. Surprisingly, the industry uses the allowable leakage rates of FCI 70.2 for the isolation valves, even though it is a standard for “Allowable Leakage Rates for Control Valves”.


Valve standards have developed over the last century, thanks to organizations that care about safety and product quality. Through this blog, we learned the big four about the organizations that set standards that dictate valves and the rating systems that are commonly used. Next time you look at a valve, try to recognize the rating markings!