The velocity profile shows the maximum (red line) and minimum (green line) velocity over the length of the profile. If you have the calculation option set to generate animation data, you can navigate through time and see the "current" HGL (black line) change. A large difference in these velocity lines on either side of an air valve indicates that the flow and/or the diameter is different. Assuming that all pipes are the same diameter, the difference you see is likely due to some assumptions behind the air valve element. After the transient conditions settle down after your pumps shut down, the hydraulic grade will likely remain lower than the air valve locations (the air valves will remain open). In reality, the pipes would drain our partially, settling the flow (and velocity) to a new steady value. However, by default, HAMMER cannot track the liquid/air interface along the length of the pipe and will instead assume that the pocket is concentrated at the air valve location. Therefore when the HGL drops to the air valve elevation and the air pocket starts forming, the hydraulic grade will remain roughly equal to the air valve elevation. So, with the pumps off, the hydraulic essentially act as if the air valves are reservoirs, so the flow between them is based on the flow necessary to induce a headloss equal to the difference in hydraulic grade. So, the bigger the difference in elevation, the bigger the flow (and velocity). So, the increase you highlighted on the left side (AV-1) is likely caused by the flow being zero (or near zero) on the left side of the air valve (flat HGL extending to the left of AV-1) and positive/higher flow on the right side of the air valve (the flow needed to bring the HGL from ~6.5 m (AV-1) to ~5.9 m (AV-2) I encourage you to enable the animation option ("generate animation data" in the calculation options) and animate both profiles to get a good visual of how this is happening. Here are some other references related to this: Modeling Reference: Air Valves http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/postive-flow-in-pipe-downstream-of-element-that-is-closed With that said, I have another concern with how the initial conditions are set up. You mentioned you used the "treat air valve as junction" setting for AV2; I assume you mean you set this to "false". As you noticed, this causes the upstream pump to "see" the air valve and add enough head to lift the HGL up to the air valve elevation. The small portion of the downstream pipe not running full is interpreted as part-full flow. In other words, the air valve is open during the initial conditions, with some air in the system and open channel flow in the downstream pipe for some distance. When the HGL goes back above the pipe elevation, this indicates pressure flow has resumed. This works well for a steady state/EPS run, but the transient solver in HAMMER can have issues with this. The reason is because HAMMER assumes that pipes are flowing full in the initial conditions. So, it interprets the drop in HGL as a headloss and thinks that the pipes are flowing full. You might see an "initial surge" (movement at the beginning of the transient simulation before the pumps shut down) from this, or an air pocket may immediately start forming. In this case, it may be best to end your transient model at AV2 (put the discharge to atmosphere there). For more on this, see the section called "What if my air valve is open during the Initial Conditions?" in the above air valve modeling reference technote. If this does not help, please include a copy of the model files (zipped) either in this public thread (use the advanced reply editor to attach) or confidentially using the below method: http://communities.bentley.com/p/bentleysecurefilesupload
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