Self-pressure valve design and selection based on the following points: 1, calculate the flow of water through the valve. According to the data provided by the sample, and with reference to the size of the interface device, check whether the flow of the valve meets the requirements. 2, choose the appropriate pressure range. Calculate the water system resistance, draw the valve needs to absorb the pressure difference, to determine the pressure range of the valve. 3, According to the calculated flow, pressure range and technical requirements to determine the appropriate valve series, model. The pressure drop of the self-operated pressure differential valve is equal to the minimum pressure drop value of the working pressure difference range. Note: Pump head = pressure drop of self-operated pressure drop + other pressure drop of the system.