Abstract: A positive displacement gear pump or gear hydraulic motor having at least a first rotor with first rotor teeth and a second rotor with second rotor teeth, the first rotor teeth meshing with the second rotor teeth. First rotor chambers are defined between first rotor teeth and second rotor chambers are defined between the second rotor teeth. As the rotors mesh, the first rotor chambers, second rotor chambers or both become enclosed or substantially enclosed to form what are referred to here as secondary chambers. Pressure variations in a secondary chamber are relieved by internal flow channels in the first rotor, second rotor or both, creating a fluid connection between the first rotor chambers and the second rotor chambers. The first rotor may be an internal gear rotor or both rotors may be external gear rotors.