The selection and design of electric control valve is very important, the correct choice will affect the effect of system regulation. In addition, in order to ensure the working pressure drop and regulation performance of the electronic control valve, the manual control valve or differential pressure control valve can be connected in series.
1、 Technical parameters of electric control valve
(1) Circulation capacity
The flow of the electric control valve reflects the flow of the valve, which is defined as the flow through the valve when the pressure difference between the two ends of the valve is 1 bar. KV = q / P is usually used to indicate the flow through the control valve, i.e. m3 / h; P is the pressure difference between the front and rear of the control valve, i.e., bar. When the valve is fully opened, the flow rate is the strongest, and the value of kV is the maximum, which is called kVs; when the valve is closed, the flow rate is 0.
（2） Flow characteristic curve
The flow characteristic curve of the electric control valve reflects the relationship between the flow through the valve and the percentage rated stroke when the rated stroke changes from 0% to 100%, and also reflects the relationship between the relative flow and the relative opening of the control valve. When the pressure drop of the valve is constant, the flow characteristic through the valve is called the ideal flow characteristic; when the pressure drop of the valve changes, the flow characteristic through the valve is called the working flow characteristic.
（3） Valve weight
The valve weight of the electric control valve refers to the ratio of the pressure drop at both ends when the control valve is fully open and the pressure drop at both ends of the regulating system when the control valve is fully closed. The valve weight of electric control valve is related to the regulation ability of the system. The smaller the valve weight, the worse the regulation ability of the system; otherwise, the better.
（4） Adjustable ratio and closing differential pressure
The adjustable ratio of the electric control valve is the ratio of the maximum flow rate and the minimum flow rate that can be controlled by the regulation. During operation, the flow change should be within the controllable range of the control valve. The closing pressure difference is the maximum pressure difference at both ends of the valve when the control valve is fully closed. If the closing pressure difference of the control valve exceeds the allowable range, immediate measures (such as series differential pressure control valve) shall be taken to restore it to the normal range.
2、 Design and selection of electric control valve
（1） Selection and design parameters
The parameters that need to be considered in the design and selection of electric control valve are flow rate, pressure before valve, pressure difference, pressure and temperature after valve. Firstly, the heating load of the heating station is determined by the heating area within the heating range of the heating station, the insulation performance of the building, the type of radiator, and the heating temperature of the room; secondly, the primary side flow of the heat station can be determined by the supply and return water temperature of the primary network, and then the flow of the regulating valve can be determined; Finally, the pressure in front of the regulating valve, the pressure difference or the pressure behind the valve can be obtained from the water pressure diagram of the primary network of the heating system and the resistance loss of the heating station, which should be determined according to the actual situation of the heating system.
（2） Design selection principle
The best principle of heat supply system regulation is that the change of valve opening is linear with the change of heat exchange of heat exchanger. The heat transfer characteristic of water water heat exchanger in thermal power station is an up throw curve, so equal percentage of flow characteristic control valve should be selected. In addition, in order to ensure the regulation performance in practice, the valve weight of the control valve should not be less than 0.25 ~ 0.3. The valve body diameter of the electric control valve should be selected according to the kVs of the flow capacity, and the selection of the actuator should meet the requirements of the maximum closing pressure difference.
（3） Design selection calculation
According to the heating load of the heating station and the temperature of the primary side supply and return water, the flow rate of the electric control valve is calculated; the pressure drop of the electric control valve is determined according to the water pressure diagram of the primary network, the resistance of the thermal station and the valve weight; the required Kv value is calculated; the type selection sample of the electric control valve is searched, and the kVs value larger than the Kv value and in the same gear is selected, and the diameter of the regulating valve is selected; Calculate the pressure drop when the control valve is actually fully opened, and then calculate the actual valve weight, which should not be less than 0.25 ~ 0.3; check the allowable pressure difference and allowable temperature in the selection sample and select the valve type; select the actuator matching with the valve body according to the selection sample, and meet the requirements of closing differential pressure, and determine the type of control signal.