Rotary positive displacement device

A rotary positive displacement device, comprising:

• a housing having a low pressure port and a high pressure port;
• a first rotor having a frusto-spherical outer surface, an axial surface, a first rotor shaft and a first rotational axis passing through the first rotor shaft, wherein the axial surface comprises at least one teardrop surface and at least one involute surface, the at least one teardrop surface and at least one involute surface together defining at least one lobe and a corresponding valley;
• a second rotor having a frusto-spherical outer surface, an axial surface, a second rotor shaft and a second rotational axis passing through the second rotor shaft, the axial surface comprises at least one teardrop surface and at least one involute surface, the at least one teardrop surface and at least one involute surface together defining at least one lobe and a corresponding valley, the second rotational axis intersecting with the first rotational axis;
• a high pressure opening extending between the first and second rotors and the high pressure port of the housing;
• a low pressure opening extending between the first and second rotors and the low pressure port of the housing, wherein the low pressure opening is configured to selectively communicate with one or more chambers of at least two chambers;
• wherein the second rotor is configured to intermesh with the first rotor such that the at least two chambers are separated by the axial surfaces of the first and second rotors, each chamber of the at least two chambers having a variable volume as the first and second rotors rotate about their respective rotational axes;
• and
• wherein a lobe tip of each rotor is in contact with, so as to form a seal against, the corresponding teardrop surface of the other rotor;
• and
• wherein the involute surface of each rotor is in contact with, so as to form a seal against, the corresponding involute surface of the other rotor;
• and
• wherein the high pressure opening comprises a lower edge, the lower edge positioned along an outer diameter of the frusto-spherical outer surface of the second rotor, wherein the lower edge is positioned between the second rotor shaft and the at least one valley of the first rotor.