Abstract: The present invention discloses a rotary machine, such as a motor or a pump, which works with a fluid in the form of a gas or a liquid. The rotary machine comprises a housing, an annular passageway arranged in the housing, and at least two rotor-driven blades which run in the annular passageway and which are movable radially in the rotor. The passageway includes a fluid inlet, a fluid outlet and a constriction located therebetween in the passageway. The radial movement of the blades is guided forcibly past the constriction. Each blade is pivotally connected to a counterweight arranged on an arm. The arm is pivotally journalled on the rotor between the counterweight and the pivotal blade connection.