Operating Points of Multiple Lift Stations with Common Force Main

[MB2L]

I am working on a hydraulic analysis of an existing pump station that has two larger pumps with one slightly smaller pump that ties in downstream. Due to the system layout and small pipe size, there is the potential for significant differences in minor losses.

I am trying to verify model results at this point and get a better understanding of what is happening. I set up a spreadsheet to run system curves based on different ratios of flow going to the smaller pump (P3 in the attached drawing) and the two larger pumps (P1 & P2). I have separate system curves for Pipes C&D and Pipes A,B,&D. The attached graph shows my pump curves and system curves based on the ratio of flow calculated by the model (the operating conditions in the model are shown with the dotted lines).

My question lies in verifying the operating point and the corresponding ratio of flow in Pipe B and Pipe C. With 2 different system curves, it seems logical that the flow in Pipe D would be somewhere between the intersections of the system curves and the “3 Pumps On” curve, and the model results reflect this. The graph indicates that the headloss is calculated correctly at the flow QD calculated by the model. However, how do I verify the right proportion of the flow is going to each pipe? In addition, how do I check the accuracy of flow QD since there are two intersections of system curves and pump curve?

Thanks in advance.

 

[MB2L]

Here is the other link...

 

[bimr]

Don't believe that there is any method to accurately predict the flows with the scenario that you have. The best that you can do is to estimate the flows.

For a pump station of this capacity, you should have a flow meter. A flow meter will enable you to most accurately determine the flow data.

If you do not have a flow meter, you can rent one for testing.

 

[MB2L]

Thanks bimr. Flow data (and corresponding pressure data) is something that we have requested, so hopefully we are able to get that soon.

Originally I tried iterating by plotting a system curve for Pipe B based on an assumed flow QC. I then assumed a flow QB based on the point where the system curve crossed the "3 Pumps" curve. I then repeated the process for Pipe C using the new assumed QB with a goal of finding a single operating point on the "3 Pumps" curve. However, this assumes that headlosses are equal in Pipes A+B and Pipe C, which is not true.

Does anyone know of an iterative process to check that the right flows are being calculated by the model (based on the assumptions of C, etc. used during the input of data)?