Various characteristics of control valves

Control valves are used to regulate the flow, pressure and level of the medium. According to the signal of the adjustment part, the opening of the valve is automatically controlled, so as to achieve the adjustment of medium flow, pressure and liquid level. Control valves are divided into electric control valves, pneumatic control valves and hydraulic control valves. There are two commonly used types of control valves: electric control valves and pneumatic control valves.

The control valve is composed of two parts: electric actuator or pneumatic actuator and control valve. The latter has the characteristics of large flow capacity, small unbalance and stable operation, so it is usually especially suitable for occasions with large flow, high pressure drop and less leakage.

Flow-through capacity Cv is one of the main parameters for selecting the control valve, and the definition of the flow capacity of the control valve is as follows: when the control valve is fully open, the pressure difference between the two ends of the valve is 0.1MPa, and the fluid density is 1g/cm3, the flow rate of the flow diameter control valve per hour is called the flow capacity, also known as the flow coefficient, which is expressed in Cv and the unit is t/h.

According to the Cv value of the flow capacity, the nominal diameter DN of the control valve can be determined.

The flow characteristics of the regulating width are the relationship between the relative flow rate of the medium flowing through the regulating valve and its opening under the condition that the pressure difference between the two ends of the valve remains constant. There are three types of flow characteristics of control valves: linear, equal percentage and parabolic, and the significance of the three flux characteristics is as follows:

(1) Equipercentariness (logarithmic)

The equal percentage of relative stroke and relative flow are not in a straight line, and the change in flow rate caused by the change of unit stroke at each point of the stroke is proportional to the flow rate at that point.