Notifications on Sewer Cad V8i

June,

This is a warning that the program has set the stop invert of the pressure pipe to the wet-well base elevation.  For example, the model you had attached to the forum on why the pumps are not working, you have a pressure pipe with a stop invert of 5.236 while the max elevation in the wet-well is 5.150, and the base elevation is 1.720, so the program would compute the model with the stop invert of the pressure pipe at 1.720.

As a workaround, you may want to have the pressure pipe connect to a manhole with the elevation needed.  You would then use a large pipe to connect to the wet well.

TLFOSTER56,

Thanks for your response.

I can't get why the model will calculate at elevation 1.72, instead of 5.236 since elevation 5.236 is the real or actual elevation of the stop invert? Will you please explain further?

I'm sorry, I missed to state that, the system was already existing/working, so I cannot put manhole like what you are proposing. My goal on this model is actually to check the system, if it is working good or there should be modification to be made on the system so that it will work as expected.

So, my question was, Is that notification is really a problem? The model is still calculating even having that error, Will I still get reliable results?

Thank you very much! I really appreciate your help.

Best Regards,

June

As Terry mentioned, the notification is there to warn you of a limitation in this situation. During calculations, the program will override your selection of the stop invert of the pressure pipe and set it equal to the bottom of the wetwell. It doesn't mean that there's a problem, but rather an assumption to be aware of so that you can decide how to proceed. The model does indeed still calculate, and the results will be reliable, assuming that you're OK with the assumption of the invert being set to the bottom.

The implications of this are the same as if you manually connected the pressure pipe to the bottom of the wetwell. This means that the upstream pump will need to add less head than it would have. Depending on the pump curve and system head curve, this may not make a significant difference. This is likely why this assumption is in place, as most systems like this would see a negligible difference.

If you feel that the operating point of the upstream pump and the information you ultimately need might be effected by this assumption, the manhole workaround can be considered. You mentioned that the manhole isn't there in the real system - this is true - the manhole suggestion is a workaround in order to allow the hydraulics to behave as they would with the invert connected at a higher elevation. If your goal is to make sure that the existing system is working OK, then this should not be a concern - if the pipe between the "fake" manhole and the wetwell is hydraulically insignificant (large and smooth), it will not effect the results, and the model should act just as it would in the field where the upstream pressure pipe is connected directly to the wetwell at an elevation higher than the bottom. From doing this, you could also compare the results to that with the pipe connected directly to the bottom of the wetwell, as a sensitivity analysis. If the end results you need are not noticeably different, then you might conclude that the manhole workaround is not necessary.

We can look into improving SewerCAD in the future to allow a pressure pipe to be connected directly to the upstream side of a wetwell at an elevation higher than the bottom (reference # 136510).