A pump unit includes a rough-vacuum pump and a Roots vacuum pump connected in series and upstream of the rough-vacuum pump in the direction of flow of the pumped gases. The Roots vacuum pump has three pumping stages in which the rotors are designed to be driven simultaneously in rotation by a motor of the Roots vacuum pump. A ratio of the flow rate generated by the first pumping stage of the rough-vacuum pump in the direction of flow of the pumped gases over the flow rate generated by the last pumping stage of the rough-vacuum pump is less than or equal to four.

A blower assembly includes, but is not limited to, a blower housing defining a blower chamber and including a gas inlet and a gas outlet; a first rotor positioned within the blower chamber and adapted for rotation therein, the first rotor including a first shaft and at least two lobes defining a first lobe profile; and a second rotor positioned within the blower chamber and adapted for rotation therein, the second rotor including a second shaft and at least two lobes defining a second lobe profile, wherein the first and second rotors are formed from a metal having a coefficient of thermal expansion from about 1 (10.sup.-6 in/in * K) to about 13 (10.sup.-6 in/in * K), and wherein at least one of the outer surface of the first rotor, the outer surface of the second rotor, or the blower chamber includes a coating.

A power saving vacuuming pump system is based on complete-bearing-sealing and dry-large-pressure-difference root vacuuming root pumps includes an input valve at an input end of a vacuum space for receiving gas mixture of saturation water vapor and non-condensed air from a condenser of a power plant; a first root vacuum pump connected to the input valve for receiving gas mixture from the input valve and then compressing the gas mixture; a second root vacuum pump connected to the first root vacuum pump for receiving gas mixture from the first root vacuum pump and then compressing the gas mixture. Inner connection walls between the vacuum chamber and the two bearing chambers are installed respective bearings which are installed to be around the driving shaft, and thus all the vacuum chamber and the two bearing chambers are tightly sealed. The vacuum chamber is completely dried so as to prevent from internal emulsion.

A multi-stage vacuum pump comprising a stator defining multiple pumping chambers is discussed. The stator comprises a plurality of transfer channels for providing a fluid passage from an outlet port of one of the plurality of pumping chambers to an inlet port of a subsequent pumping chamber. Some of the transfer channels comprise two side channel sections on opposing sides of the stator. One of the transfer channels comprises a single side channel section on one side of the stator. The vacuum pump further comprises a gas ballast inlet channel arranged on an other side of the stator to the one side of the stator.

A method of operating exhaust gas recirculation pump for an internal combustion engine including: providing an EGR pump assembly including an electric motor coupled to a roots device having rotors, the EGR pump operably connected to an internal combustion engine; providing an EGR control unit linked to the EGR pump assembly; providing sensors linked to the EGR control unit; determining if a motor speed is within a predetermined target in step S1 wherein when motor speed=predetermined target then; determining if a motor torque is within a predetermined target in step S2 wherein when motor torque=predetermined target then; determining if a motor temperature is within a predetermined target in step S3 wherein when motor temperature=predetermined target then; and maintaining operation of the exhaust gas recirculation pump.

A pump unit includes a rough-vacuum pump and a Roots vacuum pump connected in series and upstream of the rough-vacuum pump in the direction of flow of the pumped gases. The Roots vacuum pump has three pumping stages in which the rotors are designed to be driven simultaneously in rotation by a motor of the Roots vacuum pump. A ratio of the flow rate generated by the first pumping stage of the rough-vacuum pump in the direction of flow of the pumped gases over the flow rate generated by the last pumping stage of the rough-vacuum pump is less than or equal to four.

A pump assembly may include a rotor having a rotor shaft portion; a stator having a bore portion defining a bore for receiving the rotor shaft portion; and a circumferential protrusion extending radially into the bore between the bore portion and the rotor shaft portion, wherein at least one of the protrusion and a corresponding surface of the rotor shaft portion or the bore portion is configured to be abraded by the other upon experiencing contact therewith. In this way, the gap between the bore portion and the rotor shaft portion may be at least partially filled by the circumferential protrusion in order to provide a seal. The protrusion and one of the bore portion and the rotor shaft portion may be formed from different hardness materials.

A driving structure of a three-axis multi-stage Roots pump comprises a pump body, wherein a gear end cover is mounted at one side of the pump body, an air outlet end moving bearing air sealing unit is mounted on the other side of the pump body, and the bearing end cover is mounted on the pump at the side of the pump body; a driving axis, a first driven axis and a second driven axis are further provided inside the pump body, and the driving axis is connected with the first driven axis and the second driven axis through the gear, respectively; and both ends of the driving axis, the first driven axis and the second driven axis are movably connected to an air inlet end gear mechanical seal driving unit and an air outlet end moving bearing air sealing unit, respectively. The present invention overcomes the deficiencies of the prior art, a fixed bearing limiting unit not only plays a radial supporting role, strengthens the rigidity of an independent axis, but also reduces the diameter of the axis, and at the same time, evenly distributes to the two axial ends in the axial deformation process, avoiding deformation in a single direction, reducing the amount of displacement by nearly half, and also improving the sealing efficiency of the system.

A twin shaft pump may include two cooperating rotors configured to rotate in opposite directions about parallel axes of rotation; a stator comprising a stator bore in which the rotors are mounted to rotate. The stator bore includes a central part between the two axes of rotation, and an outer part outside of the two axes, the rotors being configured to have cooperating dimensions with the stator bore such that an outer edge of each rotor that is remote from the other rotor seals with the stator bore when rotating in at least a portion of the outer part. A fluid inlet is provided in the stator bore, at least a portion of the fluid inlet being in the central part of the stator bore between the axes of rotation. A fluid outlet is provide in an opposing surface of the stator bore, the fluid outlet being in the central part of the stator bore. The fluid inlet and fluid outlet are arranged such that on rotation of the rotors, the rotors each move a pumping chamber between the fluid inlet and the fluid outlet; wherein at least a portion of the fluid inlet is arranged to extend beyond the central part of the stator bore.

A multi-stage dry Roots vacuum pump, including a pump body, multi-stage Roots working units and a plurality of drive components. The pump body is provided with a plurality of independent working chambers, and airflow channels communicating the various working chambers; the airflow channels are communicated with outside; the Roots working units of each stage include driving Roots rotors and driven Roots rotors; the driving Roots rotors and driven Roots rotors are positioned in the working chambers; and the various drive components are respectively used for driving the driving Roots rotors and driven Roots rotors positioned in the various working chambers to rotate towards opposite directions at the same rotating speed. The Roots working units of various stages may be randomly distributed at various positions of the pump body on premise of ensuring that the airflow channels can communicate the working chambers of each stage.