Factors to consider for surge analysis

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.

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

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.

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.

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.

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.

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.

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.

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

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.

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.