Types of Shutoff ClassificationsĪNSI Class I – The ANSI Class I shutoff is an open classification that does not require a test, while allowing for a specified agreement between the user and the valve manufacturer as for the required leakage. The following briefly describes each shutoff classification and maximum leakage rates for each. Shutoff classifications range from ANSI Class I, where the valve does not require tight shutoff, to ANSI Class VI, where shutoff must be completely or nearly bubble tight.

Shutoff classifications are determined by a percentage of a test fluid (usually water or air) that passes through the valve, as part of valves rated capacity. Specifically, ANSI Standard 70-2 provides the outline for six shutoff classifications. Industry standards have been established for the control valve’s regarding the amount of permissible leakage of the process fluid through the valve’s seat. Although closed, there is an “allowable leakage rate” as part of each control valve’s specification.

Often when commissioning or troubleshooting automatic control valves, there’s a discovery that the control valve, even though fully closed, doesn’t fully shut off the flow of process fluid through the plug and seat.

Valve steam controller manual shutoff