About using tanks as surge protection devices

When using InfoSurge to model a water distribution system, one of the ways to prevent hydraulic transients, or surge events, is by implementing tanks, one of several types of surge protection devices (SPDs).

The inclusion of a surge tank in a system can make a significant difference during a surge event.

Effect of a Surge Tank:

Consider what happens when a surge tank is added on the upstream side of a valve.

This example surge analysis shows that following a 2-second valve closure, water pressure can spike and drop rapidly, going low enough to reach cavitation levels.

A surge tank drastically smooths out these pressure changes, greatly reducing the potentially damaging effects of a surge event.

Input Data and Tank Performance:

It is important to understand how input data impacts tank performance.

For a valve to work properly, correct values must be assigned for factors such as:

• Inflow and outflow diameter
• Opening and closing time
• Inflow and outflow resistance
• Tank volume

Also important to understand the meaning of model output fields.

For more information on input and output data, visit the InfoSurge help pages on the Autodesk website.

Supported Tanks:

InfoSurge supports commonly used tanks as surge protection devices, including:

Open surge tanks:

Can be installed only in locations where normal static pressure heads are small.

Two purposes:

• To prevent high pressure due to upsurge by receiving liquid
• To prevent cavitation due to downsurge by providing liquid to an area of low pressure

One way (feed) surge tanks:

Open or closed tanks equipped with a check valve to allow flow only into pipe system.

Can be installed anywhere on the line and are used to avoid cavitation.

Water is discharged from feed tank into pipe system when low pressures develop.

Closed (compressor) surge tanks:

Surge vessels equipped with compressor to maintain desired initial water level—and air volume—under normal operating conditions.

Commonly used at pump stations.

Closed (bladder) surge tanks:

Surge vessels that have a pre-charged bladder with set pressure to maintain desired air column under normal operating conditions.

A compressor is not required.

Often located where no power is available.

Surge Analysis Considerations:

If the function of a specific tank is understood, a model SPD can be found to match that behavior.

Note that in a surge analysis, SPDs are placed on a junction.

IMPORTANT: A junction with an SPD must have only one pipe connected to each side, or InfoSurge displays the error message: “Invalid pipe connection at surge protection device”.