A liquefier assembly for use in an additive manufacturing system to print three-dimensional parts, the liquefier assembly comprising: a first drive mechanism configured to feed a consumable material; a liquefier tube configured to receive the consumable material fed from the first drive mechanism and to melt the received consumable material to produce a molten material in a pressurized state; and an extruder comprising a gear assembly characterized in that the gear assembly has a first gear (100, 104) and a motor that turns the first gear (100, 104), wherein rotation of the first gear (74, 76) regulates a flow of material out of the extruder, wherein the gear assembly further comprises: a casing assembly (64, 66, 68) having an inlet opening configured to operably receive the pressurized molten material from the liquefier tube and an interior cavity configured to receive the pressurized molten material from the inlet opening and an outlet opening wherein the gear (74, 76) is a pump member within the interior cavity of the casing assembly (64, 66, 68); and wherein the gear (74, 76) is a first gear disposed within the interior cavity, and configured to rotate under motorized power and further comprising a second gear engaged with the first gear wherein teeth (102, 106) of the first gear and second gear are enmeshed such that the second gear is configured to counter rotate with the rotation of the first gear, wherein the rotations of the first gear and the second gear regulate a flow of the pressurized molten material from the inlet opening around the gear assembly and to the outlet opening; a second drive mechanism configured to feed a second consumable material; a second liquefier tube configured to receive the second consumable material fed from the second drive mechanism, to melt the received second consumable material to produce a second molten material in a pressurized state; and wherein the inlet opening in the casing assembly (64, 66, 68) is also configured to operably receive the second pressurized molten material from the second liquefier. a first drive mechanism configured to feed a consumable material; a liquefier tube configured to receive the consumable material fed from the first drive mechanism and to melt the received consumable material to produce a molten material in a pressurized state; and an extruder comprising a gear assembly characterized in that the gear assembly has a first gear (100, 104) and a motor that turns the first gear (100, 104), wherein rotation of the first gear (74, 76) regulates a flow of material out of the extruder, wherein the gear assembly further comprises: a casing assembly (64, 66, 68) having an inlet opening configured to operably receive the pressurized molten material from the liquefier tube and an interior cavity configured to receive the pressurized molten material from the inlet opening and an outlet opening wherein the gear (74, 76) is a pump member within the interior cavity of the casing assembly (64, 66, 68); and wherein the gear (74, 76) is a first gear disposed within the interior cavity, and configured to rotate under motorized power and further comprising a second gear engaged with the first gear wherein teeth (102, 106) of the first gear and second gear are enmeshed such that the second gear is configured to counter rotate with the rotation of the first gear, wherein the rotations of the first gear and the second gear regulate a flow of the pressurized molten material from the inlet opening around the gear assembly and to the outlet opening; a casing assembly (64, 66, 68) having an inlet opening configured to operably receive the pressurized molten material from the liquefier tube and an interior cavity configured to receive the pressurized molten material from the inlet opening and an outlet opening wherein the gear (74, 76) is a pump member within the interior cavity of the casing assembly (64, 66, 68); and wherein the gear (74, 76) is a first gear disposed within the interior cavity, and configured to rotate under motorized power and further comprising a second gear engaged with the first gear wherein teeth (102, 106) of the first gear and second gear are enmeshed such that the second gear is configured to counter rotate with the rotation of the first gear, wherein the rotations of the first gear and the second gear regulate a flow of the pressurized molten material from the inlet opening around the gear assembly and to the outlet opening; a second drive mechanism configured to feed a second consumable material; a second liquefier tube configured to receive the second consumable material fed from the second drive mechanism, to melt the received second consumable material to produce a second molten material in a pressurized state; and wherein the inlet opening in the casing assembly (64, 66, 68) is also configured to operably receive the second pressurized molten material from the second liquefier.