Factors to consider for surge analysis

Any referenced datasets can be downloaded from "Module downloads" in the module overview.

Step-by-step guide

When running a surge analysis in InfoSurge Pro, there are several important factors to consider that can all affect the accuracy of the analysis:

  • Assigning individual or global pipe wave speeds
  • Modelling pressure sensitive demand
  • Understanding the roles of different types of valves and pumps

Pipe Wave Speed:

It is important to define a pipe wave speed for each individual pipe in the network.

In the Pipe Surge Data dialog box, an example Wave Speed is entered.

A global wave speed can be assigned to all pipes, but doing so provides less accurate surge analysis results.

The Run Manager, Surge tab, with the Global Wave Speed setting highlighted in red.

Because pipe materials can vary, especially in larger networks, wave speeds should be assigned based on individual pipe materials.

Using the correct wave speed is essential for accurate calculation of the magnitude of pressure surges in the system.

Pressure Sensitive Demand:

Pressure drops can significantly impact demand within a network.

Taking this into account can increase accuracy of surge analysis.

In the Run Manager, can enable Pressure Sensitive Demand.

Set Intrusion Calculation Method, Exit Head, and Leakage Factor/Constant to more accurately calculate the role demand plays during a surge event.

The Run Manager, Surge tab, with the Pressure Sensitive Demand settings highlighted in red.

If not enabled, analysis is performed with assumption that demand should not be adjusted to compensate for pressure loss.

Response Time:

During surge analysis, important to factor in response time—time it takes for a surge wave to travel and return to origin.

Can be important in surge considerations, such as how long it may take for a valve to open and close.

The formula, Response Time equals 2L over C, where L is the length of pipe and C is wave speed; and a graphical representation of the distance between a valve and the end of a pipe, marked with a dotted line as “L”.

Non-Active Valves:

The role of non-active valves during surge analysis must be considered.

A non-active valve is one that remains in its initially set position during analysis.

Only a throttle control valve (TCV) can have its setting changed to produce a transient.

In the Model Explorer, a zoomed-in view of the Type drop-down for valves, with Throttle Control Valve highlighted in yellow.

All other valves are non-active, including:

  • Pressure reducing valves
  • Pressure sustaining valves
  • Pressure breaker valves
  • Flow control valves
  • General purpose valves
  • Float valves
  • Vacuum breaker valves

Should have only one pipe connected to each side

Must be assigned a Type, Elevation, Diameter, Setting, and Minor Loss coefficient

Active valves have the same connection requirements but require different data settings to function properly, such as being set to a TCV.

A graphical representation of a non-active valve with only one pipe connected to each side; and the Model Explorer valve settings, with values in the Type, Elevation, Diameter, Setting, and Minor Loss coefficient fields.

Regulating Valves:

Modeled as fixed resistance (headloss) devices, with resistance calculated using steady state conditions.

Pressure reducing valves (PRVs), pressure sustaining valves (PSVs), and flow control valves (FCVs) can act as regulating valves.

In two side-by-side images, the Active Valve Data dialog box with Regulator Data highlighted in red, and the Model Explorer, with pressure settings also highlighted in red.

Note that regulator settings for PRVs and FCVs can be assigned through the Active Valve Data dialog box—if not assigned, will likely behave differently than expected and more like an open pipe.

Active Surge Valves:

Steps to create an active surge valve (overview):

  • Set the valve type to TCV.
  • ID the valve Cv (flow coefficient) vs. stem position data.
  • Use the Curve Generator to create and save a curve, and to assign that curve to the TCV.
  • Review the curve data in the Curve dialog box.

In two images side-by-side, the Active Valve Characteristics Curve Generator dialog box and the Curve dialog box, with an example of data from a throttle control valve.

Note that an active surge TCV provides two additional capabilities for transient analysis—check valve and bypass.

The Active Valve Data dialog box, with Bypass Installed and Check Valve Installed options selected and highlighted in red.

Considerations for Pumps:

If a pump is going to be active during a surge event, first specify a check valve or pump file, as necessary.

InfoSurge Pro does not automatically model a check valve on discharge side of a pump—critical to assign if the pump does have a check valve.

InfoSurge Calculator dialog box allows for setting Pump Inertia and a Pump File, which is critical for the most accurate pump trip analyses.

In the InfoSurge Calculator dialog box, settings for the selected Pump Inertia/Pump File calculator.

Like valves, pumps have connection restrictions— only one pipe can be connected to each side.

Pumps can include check valve with or without non-reopening option, and/or bypass line.

  • Check valve prevents flow reversal through the pump.
  • Bypass line allows flow to bypass pump when suction head exceeds discharge head.