There are some minor differences in network component data/representation between a steady-state (InfoWater Pro) model and a transient (InfoSurge) model and some care must be exercised to ensure proper surge model representation is ready for analysis.

Existing project data should be slightly modified to meet these requirements prior to performing a transient analysis when using InfoSurge. It is important to note that InfoSurge allows the user to run a steady state analysis and check the results. To do this, click on the Hydraulic Run Only option in the Surge Tab of the Run Manager dialog box as shown below.

This is always recommended to ensure that the system is operating properly under the steady state equilibrium. For example, if a system is initially experiencing negative pressures under steady state conditions you should fix these problems before running a surge analysis.  

When a surge analysis does not run correctly, you can use the Report toolbar button, next to the Run button, to open the report (SURGE.RPT) text file in Notepad. This will list the analysis report and outline any problems, errors or warnings. Generally, the first thing is to check the “Hydraulic Run Only” check box and re-run the surge analysis. This can give some idea if the error originates in the non-converged steady state simulation or if it originates in the surge analysis. In many cases, it is from a failure of the steady state run. You can go back to the Run Manager Standard tab to resolve the problems prior to starting the Surge analysis. For example, all of the check valves in the model will be ignored for all the pipes (pipes with an associated check valve) during the surge run and the user may have to make sure that all the pipes for the surge model have no check valves in the steady state analysis. Also, any surge options (e.g., check valve installation) for valves and pumps will be considered in the "Hydraulic Run Only" analysis but will be ignored in a standard steady state run. The table below summarizes the modeling restrictions and differences for the various network components:

Some additional information concerning these restrictions is discussed below.

Active Valves – An active valve is used to describe a variety of valves with potential changes in their stem positions during a transient analysis. These valves are modeled as a motorized throttle valve (Throttle Control Valve) in InfoWater Pro. The initial setting for valves in the steady state condition will be overwritten by the Stem Change Curve. As a result, normally closed valves will be open in the surge analysis if the initial condition of the Stem Change Curve is open or normally open valves will be closed in the surge analysis if the Stem Change Curve for that valve is set to closed.

Pipes – InfoSurge provides the option for InfoWater Pro to close a pipe; however, the closed option is the same as removing the pipe (actually, it will set the pipe diameter to zero to allow no flow through the pipe). As a result,  the surge response to the pipe would not be simulated correctly. Because of the importance of the location of closed valves for surge analysis, closing pipes must be done using a closed active valve. It should be noted that for surge analysis models, pipes cannot include a check valves although a check valve can be included for the steady-state model. For surge models, check valves are designated at nodes (such as pumps and active valves). If a check valve is closed during the steady state condition, then the element that incorporates the check valve will be initially closed. If conditions are appropriate, the element check valve will open during the transient analysis.

Pumps – The initially closed setting for pumps in the steady state condition will be overwritten by a Speed Change Curve so that the pumps will be open in the surge analysis if the initial condition of the Speed Change Curve is set to open. InfoSurge will automatically generate a three point (quadratic) head-flow characteristic curve for all pumps described by constant power input (horsepower or kilowatts) or by design point curve. For pumps described by a multiple point curve (more than three data points), only three data points will be utilized by InfoSurge (the data points will automatically include the steady-state operating head-flow data point). These pumps should be used for transient analysis only if they always operate in the normal zone of operation (positive head-positive flow). All pumps can include a check valve (to prevent reverse flow through the pump), a non-reopening check valve (a check valve that does not re-open once it is closed), and/or a bypass line (allows flow to bypass the pump when the suction head exceeds the discharge head). A Pump File (Number 1 through 9) should be employed if the pump will be operated abnormally during transient condition (flow reversal, turbining, etc.).