Applies To Product(s): Bentley HAMMER Version(s): 08.11.xx.xx Environment: N\A Area: Modeling Subarea: N\A Original Author: Nancy Mahmoud, Bentley Technical Support Group Problem How to resolve the following user notification: "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect". Solution Because of HAMMER's assumption of pressurized pipes, the occurance of sub-vapor pressure in the initial conditions means that you would actually have a vapor pocket at that location, before the transient event even starts. Basically it means the model is not in a true steady state and the model needs to be fixed so that the pressures are correct. The solution to this is different for every model, as there are a number of factors that effect the pressure at a node. Trace the HGL from that node to the upstream boundary condition to get a better idea of why the pressure is that low. In some cases, these negative pressures could occur at a high point where an air valve would actually exist. In such a case, you can set the air valve property "Treat as junction?" to False. and the program will know to have the upstream pump add enough head to overcome the high point. You may still end up with negative pressure downstream of the high point though, which means that the pipe will not be flowing full past the local high point at that flow rate. (It may flow full at other flow rates.) If the pipe is flowing partially full, then you may need to reevaluate your downstream boundary condition. The equations in HAMMER are based on full pipes. Once you get to partly full pipes, you need to change the approach. The dowstream end of the HAMMER model should be the last pipe that is flowing full (crest of the last high point). You could end the system at a reservoir, demand or discharge to atmosphere element.
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