Abstract: A positive-displacement machine includes a hollow housing provided with two diametrically opposed bores each having a first end communicating with an interior of the housing and a second end closed by a cover. A rotor member is adjustably displaceable in the interior of the housing due to displacement of two pistons positioned in the bores. The pistons are connected to a high pressure chamber, to thereby create in the pistons pressure sufficient to move the latter, to thereby move the rotor member. The housing is provided with control devices to change the pressure in the bores and create a pressure differential in the bores sufficient to move the rotor member into a predetermined position.