Abstract: A shaft seal system to prevent pressurized working substances contained within a rotary machine from escaping to surrounding areas of relatively lower pressure includes a first seal disposed between a high pressure region and a first region operating at a relatively lower substantially constant pressure. A second seal is disposed between the high pressure region and a second region operating at a relatively lower variable pressure. Sealing fluid is delivered to the high pressure region whereat the fluid flows axially in opposite directions along the shaft to the first and second regions. The flow of fluid toward the second region is restricted to a greater degree than the flow of fluid toward said first region. Changes in the flow of fluid through said first and second seals to the first and second regions resulting from changes in the operating pressure of the second region are monitored.