Valve is installed in the pipeline, the valve is working together with the entire pipeline system, the valve opening changes in the impact on traffic flow must be determined through the hydraulic system of the entire system. In fact, when the water flow through the valve has a partial resistance role, set the valve local resistance coefficient ζ, the pipeline of the water area F, water density Ï, when the valve fluid pressure p1, valve fluid pressure p2, p1, p2 The flow rate through the valve is Q = (F / √ζ) √ [2 (P1-P2) / Ï] The valve coefficient of local resistance ζ changes with the valve opening, so the flow rate is Opening changes, this change can only be obtained experimentally. If the flow is Qmax at full open (100% opening) and the flow at open X% Q = f (X%) * Qmax, where the function is experimentally determined and given as a curve for future reference . In the simplest case, f (X%) is a straight line, that is, the flow is proportional to the opening. In this case, the flow Q = f (X%) * Qmax = 0.25Qmax at 25% of the valve opening.