Hi I'm vishal
How does the tank supply the demand when it is more than the capacity of the tank?

Question

I'm running steady state and demands are more than tanks capacity, I mean how the Demand is met if capacity of tank is less than demands?

Jesse Dringoli · Accepted Answer

Vishal, the model solves around the assumed boundary conditions and demands. The elevation of the junctions only allow the pressure to be calculated. For example if there is a local high point, the energy balance does not know that more head needs to be added to overcome that elevation, with potential part-full flow if an air valve is open. See more details on that here . 
 In your case water will flow out of the tank based on any assumed demands you have entered downstream, or assumed hydraulic grade you have defined at reservoirs or other tanks, and the model solves the energy balance around that. In your case you would see a negative pressure reported at the junction whose HGL is below the node physical elevation. More details on that can be found in this Wiki article: 
 Troubleshooting negative pressures at pumps, junctions, & other node elements 
 What this tells you is that the real system may not be able to operate and that you must change something in order to resolve the problem.

Tanay Kulkarni · Answer

Hello, 
 In a steady state simulation, Only the initial water level/ elevation in the tank is considered for hydraulic analysis of the network. No volumetric analysis is done/ considered in Steady State Simulation (No consideration for Tank's Diameter). Hence, a tank is considered as an unlimited source of water at a fixed initial HGL. Hope that answers how tanks with lesser volume/ capacity satisfies more/ higher demands in steady state without any errors/ notifications. 
 However, if you want to understand the volumetric fluctuations in the tank, it is advisable that you model it in extended period simulation mode. 
 P.S. In order to make sure that the tank capacity is appropriate, the user must perform mass balancing of tanks for a certain demand and then determine the diameter accordingly. For existing tanks in the network, you can modify the Zone Boundary for the existing tank so that the demands in the revised zone will satisfy the mass balancing criteria. As a thumb rule, a tank's capacity (Vol.) is typically 1/3rd of the total demand on to it. 
 Happy modelling, 
 Regards, 
 Tanay

Yashodhan Joshi · Answer

Hello, 
 In addition to Tanay's response you can find out more about extended period simulation and tank operating range from the following articles; 
 Run an Extended Period Simulation (EPS) 
 Understanding Tank Operating Range 
 Hope this helps.

Sushma Choure · Answer

Hello Vishal, 
 The notification means that tank becomes empty at 1 m as the water is drained out completely before it becomes full. You can add controls on pump -on& off, if you have in the model based on the tank levels. So that tank is continuously filled as per the levels. 
 Below technote explains how to setup controls in the model, please go through it. 
 Creating Controls - Conditions, Actions, and Control Sets (CONNECT Edition and V8i SELECTseries 6) 
 Since you are a new user, please go through the below learning resource of WaterGEMS/WaterCAD. 
 https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/11933/learning-resource-guide-for-new-users-of-bentley-watergems-and-watercad

Hi I'm vishal How does the tank supply the demand when it is more than the capacity of the tank?

I'm running steady state and demands are more than tanks capacity, I mean how the Demand is met if capacity of tank is less than demands?

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