Functions And Basic Features Of 3pc Flanged Ball Valve

3PC Flanged Ball Valve Function and Feature Terminology
Spring Setting Range: 3PC Flanged Ball Valve (Control Valve) The range of actuator spring adjustment to balance actual process forces. Flow Capacity: The rated flow through the valve under specified conditions.
Clearance Flow: The flow rate below the minimum controllable flow rate when the shutoff element is unseated.
Diaphragm Pressure Range: The difference between the upper and lower diaphragm pressure ranges. This may be considered an inherent or installed characteristic.
Double-Acting Actuator: An actuator capable of providing power in either direction.
Dynamic Unbalanced Force: The net force exerted on the valve plug at any specified opening due to process fluid pressure.
Useful Area: In a diaphragm actuator, the useful area is the portion of the diaphragm area that effectively produces the output force. The diaphragm's useful area may change as it moves, typically being greatest at the beginning of its stroke and smallest at the end. Molded diaphragms have less variation in useful area than flat diaphragms and are therefore recommended. Equal Percentage Flow Characteristic: (See "Process Control Terminology": "Equal Percentage Flow Characteristic.")

Failure-Closed: A condition in which the valve closure element moves to the closed position when the actuating power fails.

Failure-Open: A condition in which the valve closure element moves to the open position when the actuating power fails.

Failure-Safe: A characteristic of a valve and its actuator that, upon loss of actuating power, causes the valve closure element to move to fully closed, fully open, or remain in its previous position, whichever position is deemed necessary to protect the process. Fail-safe mechanisms may require the use of auxiliary controls connected to the actuator.

Flow Characteristic: The relationship between flow through a valve and percentage of rated travel as the percentage of rated travel changes from 0 to 100%. This term should always be referred to as inherent flow characteristic or installed flow characteristic.

Flow Coefficient (CV): A constant (CV value) related to valve geometry for a given travel that can be used to measure flow capacity. It is the number of U.S. gallons of water at 60°F that will flow through the valve per minute at a pressure drop of 1 pound per square inch.