Generally the term RANGEABILITY is used to describe the capability of a CONTROL valve (i.e. the ratio of the MAXIMUM Cv of the valve to the minimum Cv at which it can control) whereas the term turndown is generally used to describe the requirement of an application (i.e. ratio of Cv at maximum conditions to Cv at minimum condition).

Note that the rangeability of a valve must be greater than the ratio of the Cv of the valve when fully OPEN to the CALCULATED Cv for the minimum conditions of the application.

• Turndown applies to the application and is the ratio of the calculated Cv at maximum conditions to the calculated Cv at minimum
• Rangeability applies to the valve and is the ratio of the Cv of the valve fully open to the minimum Cv at which it can control
• The rangeability of the selected valve must exceed the turndown requirements of the application.

Generally the term rangeability is used to describe the capability of a control valve (i.e. the ratio of the maximum Cv of the valve to the minimum Cv at which it can control) whereas the term turndown is generally used to describe the requirement of an application (i.e. ratio of Cv at maximum conditions to Cv at minimum condition).

Note that the rangeability of a valve must be greater than the ratio of the Cv of the valve when fully open to the calculated Cv for the minimum conditions of the application.