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When using an operating rule to gradually close a valve element (FCV,TCV, etc) in HAMMER V8 XM, why does my time history plot of flow/headstay constant and only suddenly drop at the time corresponding to 100%closure?Why do I not see a gradual change in head/flow during a transient, whena valve operating rule is configured as such?Problem Number 31635
Make sure that your valve has a minor loss/headloss coefficientspecified. For example, if the operating rule is placed on a flow control valve (FCV) and it's calculated status is inactive during the initial conditions timestep used by the transient run, then itwill be using the minor loss coefficient to determine headloss duringvalve closure. If this is the case and the minor loss coefficient iszero, there will be no headloss during the closure, until it's fullyclosed.Background information:When an FCV is active, it is producing a head loss to reduce the amountof flow. We can take the amount of head loss needed to make the flowreduction and use it to compute a discharge coefficient. The dischargecoefficient is necessary to define the relationship between head lossand discharge as the valve closes.If the valve setting is inactive, or if the calculated setting isinactive, the headloss-discharge relationship is determined by the minorloss coefficient. The program converts the minor loss coefficient to adischarge coefficient for use in the transient analysis.The loss coefficient represents the losses when the valve is fully open.A discharge coefficient will be computed based on this and the relativearea (defined in your user defined valve characteristics table.)Basically the coefficient stays the same for all closure percentages,but since the area is decreasing, the velocity increases, which is usedin the headloss calculation. So, you get a varying amount of headloss,which should be reflected in the transient results viewer.