Control valveUsed to adjust the flow, pressure and liquid level of the medium.According to the signal of the adjustment part, the opening of the valve is automatically controlled to achieve the adjustment of the medium flow, pressure and liquid level.Control valves are divided into electric control valves, pneumatic control valves and hydraulic control valves.Commonly used are electric control valve and pneumatic control valve.
The regulating valve is composed of two parts: electric actuator or pneumatic actuator and regulating valve.Regulating valves are usually divided intoStraight-through single-seat control valveThere are two types of straight-through double-seat control valves. The latter has the characteristics of large flow capacity, small imbalance and stable operation, so it is usually especially suitable for occasions with large flow, high pressure drop and less leakage.
The flow capacity Cv is one of the main parameters for selecting the control valve. The flow capacity of the control valve is defined as: when the control valve is fully opened, the pressure difference between the two ends of the valve is 0.1MPa, and the fluid density is 1g/cm3When, the flow rate of the flow diameter regulating valve per hour 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, the nominal diameter DN of the regulating valve can be determined by looking up the table.
Flow characteristics of regulating valve, Is the relationship between the relative flow 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.The flow characteristics of the regulating valve include linear characteristics, equal percentage characteristics and parabolic characteristics.The meanings of the three fluence characteristics are as follows:
The relative stroke and relative flow of equal percentage characteristics are not in a straight line relationship. The change in flow caused by the change of 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 small, and when the flow rate is large, the flow rate changes greatly, that is, it has the same adjustment accuracy at different opening degrees.
The relative stroke of the linear characteristic and the relative flow are in a linear relationship.The flow change caused by the change of unit stroke is constant.When the flow is large, the relative value of the flow changes little, and when the flow is small, the relative value of the flow changes greatly.
The flow rate changes in proportion to the two sides of the stroke, and generally has an intermediate characteristic between linear 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 the best, its adjustment is stable and the adjustment performance is good.The parabolic characteristic is better than the linear characteristic. Any one of the flow characteristics can be selected according to the requirements of the use occasion.