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Pressures below the lowest physically possible pressure in system at one or more time steps

For the attached model, the start pump elevation is 75m, and the other end elevation of this model is 51M. And even compute the initial condition, there will be the message "Pressures below the lowest physically possible pressure in the system at one or more time steps".

If Start the Transient Solver, there will be the message  "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect." for nearly all of the pipes.

Have placed some Air valves in the model. So, what should we do to next to modify the model? Could you help to review the attached model and provide some suggestions on it?

Thanks a lot

Jinlong

Parents
  • This can be an issue when you are pumping downhill with an intermediate high point. When the pump turns off, the downhill section of the pipe will drain by gravity. In some cases with a steep slope the downhill section may never flow full.

    You should first study the system and calibrate the model with WaterGEMS. Both WaterGEMS and HAMMER are based on full pipe flow. If the steady solution shows the HGL well below the pipe, you may not have full pipe flow. In that case a model like SewerGEMS which can model the draining and filling of the pipe may be more appropriate.

    Is this drinking water, raw water or sewage? If it is drinking water, having negative pressure will violate most regulations. You may need to consider something like a pressure sustaining valve or place a storage tank at the high point..

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  • This can be an issue when you are pumping downhill with an intermediate high point. When the pump turns off, the downhill section of the pipe will drain by gravity. In some cases with a steep slope the downhill section may never flow full.

    You should first study the system and calibrate the model with WaterGEMS. Both WaterGEMS and HAMMER are based on full pipe flow. If the steady solution shows the HGL well below the pipe, you may not have full pipe flow. In that case a model like SewerGEMS which can model the draining and filling of the pipe may be more appropriate.

    Is this drinking water, raw water or sewage? If it is drinking water, having negative pressure will violate most regulations. You may need to consider something like a pressure sustaining valve or place a storage tank at the high point..

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