There are numerous techniques for controlling transients in water distribution systems, some involving design and operational considerations and others the consideration of surge protection devices. For example, Pressure Relief Valves, Surge Anticipation Valves, Surge Vessels, Surge Tanks, Pump Bypass Lines or any of their combination can be used to control maximum pressures. Minimum pressures can be controlled by increasing pump inertia or by adding Surge Vessels, Surge Tanks, Air Release/Vacuum Valves, Pump Bypass Lines or any of their combination. The objective is to reduce the rate at which changes to the flow occur. The strategies by which this is achieved may be classified as either direct action or diversionary tactics.
Direct action strategies attempt to influence the behavior of the primary causes of the flow changes, such as valve or pump operations. Such actions include prolonging valve opening and closing times (two stage valve closure or opening), coordinating valve closures (multiple valves), avoiding check valve slams, proper fire hydrant operation (slow closing of fire hydrants), increasing pump inertia (addition of a flywheel), and minimizing resonance hazards. Other direct, but more costly, actions include strengthening (increasing pressure rating) or re-routing pipelines or using larger diameter pipes (lower pipeline velocity).
Diversionary tactics make use of various surge protection devices by which fluid is drawn into, or expelled from the piping system in order to reduce the rate of flow changes. Examples of surge protection devices are discussed in the previous section. These devices would normally be installed at or near the point where the disturbance is initiated such as at the pump discharge or by the closing valve (with the exception of Air Relief/Vacuum Breaking Valves and Feed Tanks).
Figure 6 illustrates typical locations for the various surge protection devices in a water distribution system.
No two systems are hydraulically the same and hence there are no general rules or universally applicable guidelines for eliminating pressure transients in water distribution systems. Any surge protection devices and/or operating strategies must be chosen accordingly. The final choice will be based on the initial cause and location of the transient disturbances), the system itself, and the consequences if remedial action is not taken. A combination of devices may prove to be the most effective and most economical. Final checking of the adequacy and efficacy of the proposed solution should be conducted and validated using InfoSurge.
The flowchart shown in Figure 7 provides a useful guide to the selection of devices for the control and suppression of pressure transients in pipeline systems.