Embodiments of an ORC system can be configured to reduce ingress of contaminants from the ambient environment. In one embodiment, the ORC system can comprise a pressure equilibrating unit that comprises a variable volume device for holding a working fluid. The variable volume device can be fluidly coupled to a condenser so that working fluid can move amongst the condenser and the variable volume device. This movement can occur in response to changes in the pressure of the working fluid in the ORC system, and in one example the working fluid is allowed to move when the pressure deviates from atmospheric pressure.