I am trying to put together a model with simple on-off controls in a wet well, but am having no luck. I can input a "pump on" elevation and a "pump off" elevation, and an initial condition, but I'm not convinced the model is cycling correctly. The diurnal curve for the system is a simple munical curve (high in the morning and evening for an hour or two), but I am getting 4 and 5 hour pump cycles. Does anyone have any advice on how to set up the wet well - pump settings to get it to cycle correctly? Someone recommended steady state, but if that's all I can do the model seems a waste of time since I can do simple modeling in a spreadsheet.
My intent is actually to model a system with 5 or 6 stations along a route, all with VFDs, and determine the drop in the peak flow (versus a simple summation of the individual peaks) as I move through the system. Any help would be greatly appreciated.
Hi,
Are you referring to SewerCAD or SewerGEMS? And which version are you running?
Regardless, my first tip would be to check the inflow into the wet well. My guess is that the pumps are working fine, but the inflow is not what you expect it to be (perhaps a unit conversion issue, or a pattern issue). You should graph the flow in the pipe entering the wet well and see if that looks correct.
Failing that, you might like to zip up the model file and attach it to this thread. Someone may be able to poke around and see an obvious issue. Bentley Technical Support are also good at troubleshooting modeling issues - support@bentley.com
Regards,
Mal Sharkey
Thanks Mal. A few quick answers - I am using the newest version of SewerCad, 8.11 I think it is. Flows are good and the wetwell is filling fine. The problem has now been narrowed down to an issue of getting the pumps to start. I've even had the pumps running as the initial condition, but when I run the model no flow leaves the wetwell. At this point I have simplified it to death and still can't get the pump to run. I have the controls down to a simple on-off at a single elevation, but the pump just won't run.
I'm sending the model ( one wetwell, one short piece of pipe, one pump, one discarge pipe, and one outfall) to Haested to see what they can find, but if you know any tricks to making the pumps work, that would be great. Thanks.
The last time I saw this sort of problem, the user had two unconnected nodes just outside the pump station sitting right on top of one another. So basically, the pump discharged into a dead end.
Does the model say that the pump is running and there is no flow, or does it say that the pump is not running?
If it is the first case, you may have some elevation problem such that your system head is above the shut off head.
If it is second case, you may be setting the pump to run on level, but the on'off values are HGL (or vice versa).
Thanks for the help Tom. It's the second case. We were using elevations in the control set up, and not the "depths", so our "pump on" level was set about 1000' too high. I can't say we have it all working now, but the system is cycling.