Pressure transient control: Part I — criteria for transient analysis and control

Pressure transient propagation is a wholly natural consequence of any change in operating conditions for a fluid carrying system. Rapid changes in flow conditions generate surge conditions that may result in system failure. The analysis of these phenomena has progressed over the past 100 years from empirical research aimed at the protection of large-scale pipeline and plant networks to the development of computing simulations to support system design. Pressure surge analysis is therefore a consideration in the design and operation of all fluid systems: the objective of such an analysis being the prediction, control and suppression of transients. This paper presents the background to the development of surge alleviation, from traditional pipeline protection to applications within building drainage and vent systems, thereby stressing that the system failure consequences of transient propagation are dependent on the particular system, independent of absolute surge pressure, and that system protection criteria may be developed that apply regardless of the system or the severity of the transient. Practical application: The control of air pressure transients in building drainage systems has been limited due to the need to attenuate positive pressure propagation via an open termination at roof level - a poor solution as the transient will have affected all system trap seals before reaching the relief vent. The Positive Air Pressure Attenuator - an expandable bag that controls the rate of change of entrained airflow within the system - reduces the possibility of trapseal loss due to positive transient propagation. Potentially this is a major contribution to vent system design that could revolutionize 150 years of design methodology.