Regulators are used to regulate the flow, pressure and level of the media. According to the adjustment part signal, the opening of the valve is automatically controlled to achieve the adjustment of the medium flow, pressure and liquid level. The regulating valve is divided into an electric regulating valve, a pneumatic regulating valve and a hydraulic regulating valve. Commonly used are electric control valves and pneumatic control valves.
The regulating valve is composed of an electric actuator or a pneumatic actuator and a regulating valve. Regulating valves are generally divided into two types: straight-through single-seat control valves and straight-through two-seat control valves. The latter are characterized by large flow capacity, unbalanced operation and stable operation, so they are usually suitable for high flow, high pressure drop and leakage. Less occasions.
The flow capacity Cv is one of the main parameters for selecting the regulating valve. The flow capacity of the regulating valve is defined as: when the regulating valve is fully open, the pressure difference between the two ends of the valve is 0.1 MPa, and when the fluid density is 1 g/cm3, the flow path per hour The flow rate of the regulating valve is called the flow capacity, also called the flow coefficient, expressed in Cv, and the unit is t/h.
According to the flow capacity Cv value 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 rate of the medium flowing through the regulating valve and its opening degree under the condition that the pressure difference across the valve is kept constant. The flow characteristics of the regulating valve are linear, equal percentage and parabolic. The significance of the three fluence characteristics is as follows:
(1) equal percentage (logarithm)
The equal percentage of relative stroke and relative flow are not linear. The change in flow caused by the change in unit stroke at each point of the stroke is proportional to the flow at this point, and the percentage change in flow is equal. Therefore, its advantage is that the flow rate is small, the flow change is small, and when the flow rate is large, the flow rate changes greatly, that is, the same adjustment precision is obtained at different opening degrees.
(2) Linear characteristics (linear)
The relative travel of the linear characteristics is linear with respect to the relative flow. The change in flow caused by changes in unit stroke is constant. When the flow rate is large, the relative value of the flow changes little, and when the flow rate is small, the relative value of the flow changes greatly.
(3) Parabolic characteristics
The flow rate varies proportionally to the two sides of the stroke and generally has an intermediate characteristic of linearity and equal percentage.
It can be seen from the analysis of the above three characteristics that, in terms of its regulation performance, the equal percentage is superior, the regulation is stable, and the adjustment performance is good. Parabolic characteristics are better than linear characteristics, and any of these flow characteristics can be selected depending on the requirements of the application.
