The flow characteristics of regulating valves mainly include four flow characteristics: straight line, equal percentage, quick opening, and parabolic. When installed in the actual control process, the valve differential pressure will vary with the change of flow rate. When the flow rate is low, the pressure loss in the piping section is small, and the valve differential pressure will increase, while when the flow rate is high, the valve differential pressure will decrease. This valve characteristic that differs from its inherent characteristics is called effective flow characteristic. The internal valve with quick start feature is disc-shaped and mainly used for opening/closing actions.
The flow control characteristics of the valve are determined by the flow characteristics of the valve and the combination of process piping, pumps, etc. The selection is based on the proportion of valve pressure loss in each control object and system, as shown in the table below.
The proportion of valve pressure loss in the control object system and the flow characteristics of valves
Flow control or liquid level control below 40% equal percentage flow control or liquid level control above 40% linear pressure control or temperature control below 50% equal percentage pressure control or temperature control above 50% linear