FCV vavle

My first question is whether you have an FCV in the real system. If not and you are using the FCV to force some flow, don't do it.

What is the setting on the FCV? It looks as if it is zero. If it is 0 or some value lower than 2.7, then this is what you get. If the demand is less than the setting, you have equations that can't balance and you get results that reflect this. How can you expect the model to deliver 2.7 L/s if the flow will only allow 0 L/s through it.

What are you trying to accomplish with the FCV in the model?

Dear Tom Walski

Thanks for your help.

I do this in the real system (reservoir/pump/pipes/junctions). I think that, in the fact, pressure of junction must be zero when the valve is closed. However, when I formulate on the WaterGEMS, the software noted pipe not connect and junction is negative pressure (such as that above picture)

Would you show me what kind of valve I can set in this formulation? and how do I set it?

To do that, you should use Pressure Dependent Demand which will can adjust the demand as pressure changes.

However, you would be better off using a TCV (Throttling Control Valve) than an FCV.

But why is it important to model this trivial situation? You should know that when you close the valve, no water can get to the user at the end of the line. This really won't affect pipe sizing, pump selection, etc.

Here is a related article:

communities.bentley.com/.../10506.disconnected-demand-nodes-user-notification-when-computing-model

Thanks for your help.

Eventhough I set Valve closed and PDD for junction, pressure of junction do not drop zero.

Can you show to set up to have result zero pressure at jucntion?

In the case you haven't, please have a look at this wiki about setting up pressure dependent demands. 

http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/2671.setting-up-pressure-dependent-demand-tn 

In order to understand what is going on in the model when you close a valve, you need to understand what is happening with the equations that are being solved. A closed valve is represented as a very large (but not infinite) head loss coefficient and the demand through that pipe is still met. This is why you get unexpected results.

There are several correct ways to model a closed pipe.

1. Simply set any closed pipe and nodes downstream of it to "Inactive" for that scenario in the Active Topology alternative.

2. Set the demand equal to zero in the Demand alternative for any scenario where the node is shut off. If it is only shut off for a few time steps during a run, set the demand multiplier equal to zero during those time steps.

3. User pressure dependent demand to reduce demand when a valve is closed. Be sure to set "Use Pressure Dependent Demand" to True in the Calculation Options.

In order to understand what is going on in the model when you close a valve, you need to understand what is happening with the equations that are being solved. A closed valve is represented as a very large (but not infinite) head loss coefficient and the demand through that pipe is still met. This is why you get unexpected results.

There are several correct ways to model a closed pipe.

1. Simply set any closed pipe and nodes downstream of it to "Inactive" for that scenario in the Active Topology alternative.

2. Set the demand equal to zero in the Demand alternative for any scenario where the node is shut off. If it is only shut off for a few time steps during a run, set the demand multiplier equal to zero during those time steps.

3. User pressure dependent demand to reduce demand when a valve is closed. Be sure to set "Use Pressure Dependent Demand" to True in the Calculation Options.