The control valve regulates the flow, pressure and level of the medium. According to the signal of the regulation site, the opening degree of the valve is automatically controlled so as to adjust the flow, pressure and liquid level of the medium. Regulating valve points electric control valve, pneumatic control valve and hydraulic control valve.
The regulating valve consists of an electric actuator or a pneumatic actuator and a regulating valve. Adjusted and usually divided into straight single-seat type and straight two-seat type two, the latter has a large capacity of circulation, unbalanced small and stable operation, so it is generally suitable for large flow, high pressure drop and leakage less occasions.
The circulation capacity Cv is one of the main parameters for selecting the regulating valve. The regulating capacity of the regulating valve is defined as: when the regulating valve is fully opened, the differential pressure across the valve is 0.1 MPa, and the fluid flow rate per hour is 1 g/cm3. The flow rate of the regulating valve, called the flow capacity, also called the flow coefficient, is expressed in Cv and the unit is t/h. The Cv value of the liquid is calculated as follows.
According to the size of the circulation capacity Cv check table, the nominal diameter DN of the regulating valve can be determined.
The flow characteristic of the regulating valve is the relationship between the relative flow of the medium flowing through the regulating valve and its opening degree under the condition that the pressure difference at both ends of the valve is kept constant. The flow characteristics of the control valve have linear characteristics, equal percentage characteristics and parabolic characteristics. The significance of the three fluence properties is as follows:
(1) equal percentage characteristics (logarithms)
The relative stroke and relative flow of equal percentage characteristics are not in a straight line. The change in the flow rate caused by the change in the unit stroke at each point of the stroke is proportional to the flow at this point, and the percentage of flow change is equal. Therefore, its advantage is that when the flow rate is small, the flow rate changes little, and when the flow rate is large, the flow rate changes greatly, that is, at different opening degrees, the same adjustment accuracy is achieved.
(2) Linear characteristics (linear)
Linear characteristics of the relative stroke and relative flow in a straight line. The change in flow caused by the change in unit travel is constant. When the flow rate is large, the relative value of the flow rate changes little. When the flow rate is small, the relative value of the flow rate changes greatly.
(3) The characteristic flow of the parabola varies in proportion to the two sides of the stroke, and generally has an intermediate characteristic of linearity and equal percentage characteristics.
From the analysis of the above three characteristics, it can be seen that, in terms of its adjustment performance, the equal percentage characteristic is optimal, its regulation is stable, and the adjustment performance is good. The parabolic characteristic is better than the linear characteristic adjustment performance. According to the requirements of the application occasions, any one of the flow characteristics can be selected.
The regulating valve consists of an electric actuator or a pneumatic actuator and a regulating valve. Adjusted and usually divided into straight single-seat type and straight two-seat type two, the latter has a large capacity of circulation, unbalanced small and stable operation, so it is generally suitable for large flow, high pressure drop and leakage less occasions.
The circulation capacity Cv is one of the main parameters for selecting the regulating valve. The regulating capacity of the regulating valve is defined as: when the regulating valve is fully opened, the differential pressure across the valve is 0.1 MPa, and the fluid flow rate per hour is 1 g/cm3. The flow rate of the regulating valve, called the flow capacity, also called the flow coefficient, is expressed in Cv and the unit is t/h. The Cv value of the liquid is calculated as follows.
According to the size of the circulation capacity Cv check table, the nominal diameter DN of the regulating valve can be determined.
The flow characteristic of the regulating valve is the relationship between the relative flow of the medium flowing through the regulating valve and its opening degree under the condition that the pressure difference at both ends of the valve is kept constant. The flow characteristics of the control valve have linear characteristics, equal percentage characteristics and parabolic characteristics. The significance of the three fluence properties is as follows:
(1) equal percentage characteristics (logarithms)
The relative stroke and relative flow of equal percentage characteristics are not in a straight line. The change in the flow rate caused by the change in the unit stroke at each point of the stroke is proportional to the flow at this point, and the percentage of flow change is equal. Therefore, its advantage is that when the flow rate is small, the flow rate changes little, and when the flow rate is large, the flow rate changes greatly, that is, at different opening degrees, the same adjustment accuracy is achieved.
(2) Linear characteristics (linear)
Linear characteristics of the relative stroke and relative flow in a straight line. The change in flow caused by the change in unit travel is constant. When the flow rate is large, the relative value of the flow rate changes little. When the flow rate is small, the relative value of the flow rate changes greatly.
(3) The characteristic flow of the parabola varies in proportion to the two sides of the stroke, and generally has an intermediate characteristic of linearity and equal percentage characteristics.
From the analysis of the above three characteristics, it can be seen that, in terms of its adjustment performance, the equal percentage characteristic is optimal, its regulation is stable, and the adjustment performance is good. The parabolic characteristic is better than the linear characteristic adjustment performance. According to the requirements of the application occasions, any one of the flow characteristics can be selected.
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