Control Valve Flow Characteristics

Control Valve Flow Characteristic

  The flow Characteristic of the control valve is the relationship between the flow of the in-compressible fluid that passes through the control valve and the opening of the control valve when the differential pressure at the two ends of the valve is invariable. This flow characteristic is called inherent flow characteristic.

The typical inherent characteristics include linear characteristic and equal percentage characteristic. Actually, when the control valve controls the process medium, the differential pressure on the valve will change according to the change of the opening. In this case, the characteristic curve between the opening of the control valve and the flow will deviates from the inherent flow characteristic curve. We call this kind of low characteristic as actual flow characteristic.

1. Linear Flow Characteristic

  It indicates that the flow and opening of the control valve are in the linear relationship. It is usually used for applications with small change of differential pressure, which is almost invariable. When the pressure drop on the valve becomes the main pressure drop in the system, the linear flow characteristic is often used.

 2. Equal Percentage Flow Characteristic

  It indicates the flow change rate caused due to the change of travel is in direct proportion to the original flow at the point. It is usually used in applications that require relatively wide adjusting range, or when the system pressure loss is much higher than that of the valve, or when the opening change and differential pressure change on the valve is relatively high.

 3. Quick Open

  It is mainly used for on-off control system. It is required that the flow should be high when the opening is small, and with the increase of the opening, the flow will reach the highest value very soon. After that, if the opening increases again, the change of flow is very little.