Error: Initial flow is zero, which would result in a discharge coefficient equal to 0, which is not allowed

Hello Gustavo, 

Do you mean that there are no demands at all in the model, please note that WaterGEMS is demand driven software. How are you modeling pump providing water from river to reservoir, is it like reservoir to reservoir element? 

Which software are you using here Hammer or WaterCAD / WaterGEMS? If you wish to perform transient analysis, then you should use Hammer for that. However model should be hydraulically stable and computing fine in WaterGEMS / WaterCAD before importing that into Hammer. 

For the PRVs issue, can you please upload model files for our review? If there is no flow in pipes, then there will not be any headloss. 

Sharing model files

Here is information about modeling pump shutdown, for your reference. 

Modeling a pump shut down transient event

Thank you Sushma for your answer.

Yes I am pumping from a revervoir to a reservoir elemet without demand in the irrigation net. 

I compute the initial conditions in stady state. and ithink it is hydraulically stable.

I am using Hammer and I dont have problem to model/program the shut down in the pumps. 

I upload the model files for you review.

Thank you for your help.

Gustavo, as the message indicates, HAMMER cannot compute a transient simulation for a PRV whose Status is Active, with zero initial flow. The reason is because HAMMER needs to represent the PRV initial position as a discharge coefficient (Cv), and when the valve status is active, it obtains that discharge coefficient from the calculated results from the initial conditions. In a case where the initial flow is zero, the discharge coefficient cannot be computed (see the "Discharge Coefficient Setting (Calculated) field in the Results section of the properties) and hence the error message.

To resolve this, you can set the initial status of the PRVs to Inactive, which will tell HAMMER to derive the discharge coefficient based on the fully open position, which is defined by way of the "Minor Loss Coefficient" (in your case, because "Valve Coefficient Type" is set to Minor Loss). 

See the following new article from our Wiki: "Initial flow is zero, which would result in a discharge coefficient equal to 0, which is not allowed."

Now, the the flow through all of the PRVs is zero in your model, because there are no demands in the system, and the only flow is in the trunk line between the pump station and the reservoir "BALSA". I am curious why you would have a case where the pumps are all running, but no water is leaving the irrigation system. If you intended to model the flow leaving the system via drippers/nozzles, you can enter fixed demands at the junction locations, or emitter coefficients to represent a pressure-dependent relationship. During the transient simulation, HAMMER will always treat demands as pressure dependent.

Thank you for you help.

I have tried turning PRVs to inactive but in this mode they don´t work during the transient. (Dont reduce pressure)

I have tried too an EPS simulation before the transient with demand in the begining and without demand just before the transient starts but it doesn´t work either.

The point is that some systems use the night to pump water from the river to the upper reservoir (cheaper energy and without water demand) and during the day fulfill the irrigation demand from the upper reservoir. this is the reason about that configuration.

I guess, I could solve the model adding a residual demand in each PRVs branch of the net.  

Thank you very much

Kinds Regards

Gustavo Montero said:

I have tried turning PRVs to inactive but in this mode they don´t work during the transient. (Dont reduce pressure)

Without flow, there can be no headloss, so the PRVs cannot reduce the pressure. 

Gustavo Montero said:

I have tried too an EPS simulation before the transient with demand in the begining and without demand just before the transient starts but it doesn´t work either.

When you say "doesn't work", do you mean that the PRVs are not automatically modulating to reduce pressure? First, set the status to Active if the flow is positive. Additionally, PRVs do not modulate automatically during a transient simulation unless you specify the rate of closure. See: Using Modulating PRVs

Gustavo Montero said:

The point is that some systems use the night to pump water from the river to the upper reservoir (cheaper energy and without water demand) and during the day fulfill the irrigation demand from the upper reservoir. this is the reason about that configuration.

Typically you would at least have some demand during the night hours, which would allow the PRVs to be in an initially active status (if the initial flow is positive).