A fluid energy machine having a rotor, with a casing that separates an interior from an exterior, having at least one shaft seal for sealing a gap between the rotor and casing. The shaft seal is a tandem dry gas seal, having an inner and outer seal. The outer seal has a first sealing gas feed, which opens into the gap axially between the outer and inner seal. The shaft seal has a primary discharge between the inner and outer seal, which extracts primary discharge fluid from the gap. The first sealing gas feed has a first control member for controlling the flow rate of the sealing gas. The primary discharge has a second control member for controlling the flow rate of a primary discharge fluid. The first and second control members are matched such that the first pressure is adjusted to a first pressure setpoint.