Penstock air inlet design and potential deficiency investigation

Rapid dewatering of a penstock during the emergency closure of an intake operating gate or penstock inlet valve requires adequate air admission to prevent catastrophic failure. Traditionally, air inlets were designed based on rule-of-thumb or empirical equations based on limited data. Field measurements of actual performance were infrequent and full flow closure was assumed to be activated only in emergency or catastrophic operating conditions. However, for the purpose of ensuring functionality of safety critical mechanical gates and valves, full flow closure tests have become a more common exercise at hydro utilities in recent years. Recent measurements during full-flow closure tests at BC Hydro in Canada have revealed potential deficiencies in existing designs, prompting further investigation. An engineering investigation, including hydraulic model testing and a parametric study, was conducted to understand better the air admission process and to identify key considerations for improving future designs and assessing the adequacy of existing installations.