Hello,
Background: I am modeling a sanitary sewer system that consists of 20 lift stations using SewerCAD V8i (SELECTseries3). All of the lift stations pump into a primary force main. This force main has two discharges (one at each end of the FM). Typically there is an isolation valve that splits the primary FM into two distinct systems. Let's call them the north and south systems. Occasionally there is a large demand in the north system which in the past has caused a traffic jam for other lift stations pumping into this system. To combat this issue, the maintenance team opens the isolation valve and lets flow go to either the north or south system. This has be done for many years now and has prevented long pump run times and potential overflows.
My question -
When analyzing this scenario in the model, I get a large negative flow rate at the north system discharge pressure pipe (-200 gpm) as a base flow rate (at Time = 0 or when no stations are operating). This pressure pipe discharges into a gravity manhole and pipe to the outfall. The gravity pipe flow starts at 0 gpm as expected, there is no flow assigned to the manhole.
Furthermore, on the south system discharge pressure pipe the base flow is +200 gpm when there is nothing in operation. This pressure pipe discharges directly to an outfall and the outfall flow matches the pipe flow.
It is almost like there is a ghost flow of 200 gpm going from the north outfall to the south outfall.
When stations are operating, the each discharge location shows positive flow, so I know flow is travelling to each discharge location. how it is splitting between the two discharge locations, I don't know.
As for model set up, I am using the GVF-Convex solver and an running a EPS for 24 hours. The model is able to achieve convergence. I have input multiple design points for each pump and have created controls to operate the pumps. Also, when the north and south yard systems are isolated I am getting accurate model results compared to observed data. so I am confident that the data I have enter is an accurate representation of the actual system.
Any suggestions or feedback is very much appreciated.
Thanks,
Scott
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Regards,
Sushma Choure
Bentley Technical Suppport
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.