Abstract: An improved, piston-based, pressure-transforming barrier fluid support apparatus is disclosed that can support both the pressurized and unpressurized barrier fluid requirements of a shaft-driven machine from a single unit. The disclosed apparatus includes both a pressurized section that stores, cools, cleans, and pressure regulates pressurized barrier fluid, and an unpressurized section that stores, cools, and cleans unpressurized barrier fluid. The disclosed apparatus causes debris in the pressurized barrier fluid to gravitationally migrate away from the piston, so as to prevent piston fouling. If the piston rod becomes detached, it is expelled downward for enhanced safety. Removable covers and/or a removable cylinder can provide enhanced access for cleaning and maintenance. Embodiments include a common cover that is shared by the pressurized and unpressurized sections and serves as a common manifold for cost-efficient fluid connections thereto.