Understanding hydraulic transients and their causes

Using InfoSurge to model a water distribution system is an effective way to predict and prevent pressure surges, or water hammer, from causing problems in the system.

Hydraulic transients—another term for pressure surges.

Describes disturbances in fluid caused during change from one steady-state to another.

Main components of disturbances are pressure changes caused by propagation of pressure waves throughout distribution system.

Pressure waves continue to propagate with velocity of sound until they dissipate to level of new steady-state through some form of damping or friction.

Transients can happen in several situations, such as:

• Pump startup or shutdown
• Valve opening or closing (variation in flow area)
• Changes in boundary pressures—for example, a reservoir level or pressure tank
• Rapid changes in demand conditions, such as hydrant flushing
• Changes in transmission conditions, like a pipe break

Hydraulic systems must be designed to accommodate both normal and abnormal operations and safeguarded to handle adverse external events such as power failures and pipeline fractures.

Main design considerations generally used to mitigate transient conditions include:

• Alteration of pipeline characteristics, such as pipe diameter
• Improvement in valve and pump control procedures
• Design and installation of surge protection devices

If flow is regulated extremely slowly, then it is possible to achieve smooth transition from one steady-state to another without large fluctuations in pressure head or pipe velocity.

Can use InfoSurge to model devices that control pressure and flow transients, including:

• Open surge tanks
• Closed surge vessels
• Bladder tanks
• Hybrid tanks, vented to admit air
• Bypass lines
• Check valves
• Feed tanks, which provide inflow to prevent cavitation
• Air release/vacuum valves, such as two-stage and three-stage valves
• Pressure relief valves
• Surge anticipation valves

Recognizing and addressing potential issues through transient flow simulation and analysis is essential to avoiding serious problems for water utilities.