The Katrix design is a simple and robust mechanism that uni-directionally drives a two lobe rotor in a circular-conchoidal motion, in an annular housing, where the apex seals of the rotor are in constant, positive contact with the housing. The volume of the space confined between the rotor and the housing varies as a simple sinusoidal function of the shaft angle. In addition the rotor performs in a double acting manner whereby as one side of the rotor is expelling or compressing fluid, the other side is taking in or expanding fluid. This action results in two power strokes per shaft revolution and contributes to the device’s inherently high torque and efficiency.