Ideally, a system is designed and operated to minimize the likelihood of damaging transient events. However, in reality, transients still occur; thus, methods for controlling transients are necessary. This section has two goals: (1) to make the hydraulic engineer aware of the system conditions that lead to the development of undesirable transients, such as pump and valve operations, and (2) to present the protection methods and devices that should be used during design and construction of particular systems and discuss their practical limitations.

There are two possible strategies for controlling transient pressures. The first is to focus on minimizing the possibility of transient conditions during project design by specifying appropriate flow-control operations and avoiding the occurrence of emergency and unusual system operations. The second is to install protection devices to control potential transients due to uncontrollable events, such as power and equipment failures.

Systems protected by adequately designed surge tanks are generally not adversely affected by emergency or unusual flow-control operations, because operational failure of surge tanks is unlikely. In systems protected by gas vessels, however, an air outflow or air-compressor failure can lead to damage from transients. Consequently, potential emergency situations and failures should be evaluated and avoided to the extent possible through the use of alarms that detect device failures and control systems that act to prevent them.

With most small, well-gridded water-distribution network piping, sufficient safety factors are built into the system, such as adequate pipe-wall thickness and sufficient reflections (tanks and dead ends) and withdrawals (water use). The effects of transients are most likely to result in pipe failures in long pipelines with long characteristic times (large values of 2 L/a), high velocities, and few branches. Filion and Karney (2002) found that water usage and leaks in a distribution system can result in a dramatic decay in the magnitude of transient pressure effects.