The most common features are shown in the figure above.The percentage of flow through the valve corresponds to the stem position.These curves are based on a constant pressure drop across the valve and are known as the inherent flow characteristics.
- Equal percentage – flow capacity increases exponentially with valve trim travel. Equal increments of valve travel produce equal percentage changes in the existing Cv.
- Linear – flow capacity increases linearly with valve travel.
Linear Characteristics:
• Used in liquid level or flow loops.
• Used in systems where the pressure drop across the valve is expected to remain fairly constant.
• Used when the pressure drop across the valve is a large proportion of the total pressure drop.
Equal Percentage Characteristics:
• Used in processes where large changes in pressure drop are expected.
• Used in processes where a small percentage of the total pressure drop is permitted by the valve.
• Used in temperature and pressure control loops.
