AWWA DSS62067

Negative pressures and transient pressures may affect water quality and structural integrity of distribution mains. A change in the flow rate in a full distribution main will cause a change in the pressure within that distribution main, either positive or negative. Positive transient pressures exceeding the structural strength of the distribution main will cause damage in the form of rupture or, as is more frequently the case, in the form of latent damage that results in failure at a later date. Negative pressures may cause damage in the form of structural collapse of flexible distribution main materials, and waterhammer, and may lead to the intrusion of contaminated groundwater into the water main. Advances in digital data processing systems have significantly improved our ability to continuously monitor and record negative pressures and even the very-short waterhammer event. These improvements have facilitated monitoring for transient pressures under a wide variety of circumstances. Early detection of damaging transient pressure events is now more practicable, thus permitting the reduction of damage to distribution mains resulting from these events. This paper briefly describes the causes of transient pressures and improvements in tools available to detect transient pressures. It concludes with suggestions to civil engineers and distribution main owners regarding what can be done to reduce damages from transient pressures. Includes 4 references, figures.