A system for providing a seal between a rotating part and a stationary part that comprises two seals in series separated by a cavity is disclosed. The cavity may be at low pressure and failure of either seal may be detected by a change in cavity pressure. An alarm may be triggered when cavity pressure rises above a threshold, or when it remains above a threshold for more than a predetermined period of time. In a system comprising multiple cavities, a cavity may be selectively isolated to determine if a seal associated with that cavity is experiencing a leak.