Negative Flow

Question

Hello Everyone 
 I was testing if I put high demand in junction if will give me a negative flow but that nut happen note that I know that the tank can deliver this flow 
 for example, I put 1000(GPM) in a junction that connected to the tank I already know that he can't deliver this flow with only about 3 m high difference but when I open the pipe table I see that the pipe deliver 1000(GPM) 
 how can that happen?

Gary Adams · Accepted Answer

WaterCad will ALWAYS satisfy node demands, regardless of tank levels (as long as the system is not disconnected). 
 Even if you change the size of pipes (say for instance, P-1) to be 1" diameter, you will still get a flow of 1000 gpm at node J-2. 
 That's just how the program is set up to operate. It's up to you to apply commonsense engineering to designing your system.

Sushma Choure · Answer

Hello Mohamad, 
 It appears that there is enough storage in your tank to supply the required demand, as mentioned by Gary WaterGEMS is demand driven software. However you need to look at other results as well pressures at junctions, headloss at pipes etc. 
 For now there are only demands downstream so flow out = downstream demands, in a case where there are other boundary conditions (tank or reservoir), the reservoir / source outflow will be based on the energy balance - the flow requires for those boundary HGLs to be true, while also satisfying other demands, controls, etc. 
 See also: Calculation summary: Flow Supplied, Flow Demanded and Flow Stored 
 When you enter the demands at your nodes downstream, and the pressure and other results will be calculated based on that boundary HGL, headloss in the pipes from the demanded flow, and any other constraints placed on the model such as controls, valves and other boundary conditions.

Negative Flow

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