Traditional brushless canned motor pumps have a pump section and a motor section. The motor section drives the pump section. The pump section includes an impeller having blades which rotate inside a casing. The impeller pumps fluid from a pump inlet to a pump outlet. The impeller is normally of the closed type and is coupled to one end of a motor shaft that extends from the motor section into the pump section where it affixes to an end of the impeller.
The motor section includes an electric motor having a stator and a rotor. The rotor is unitarily formed with the motor shaft inside the stator. With brushless DC motors, the rotor is actuated by electromagnetic fields that are generated by current flowing through windings of the stator. A plurality of magnets are coupled to the rotor. During pump operation, the rotor shaft transmits torque, which is created by the generation of the electromagnetic fields with regard to the rotor's magnets, from the motor section to the pump section where the fluid is pumped.
Because the rotor and stator are immersed, they must be isolated to prevent corrosive attack and electrical failure. The rotor is submerged in the fluid being pumped and is therefore “canned” or sealed to isolate the motor parts from contact with the fluid. The stator is also “canned” or sealed to isolate it from the fluid being pumped. Mechanical contact bearings may be submerged in system fluid and are, therefore, continually lubricated. The bearings support the impeller and/or the motor shaft. A portion of the pumped fluid can be allowed to recirculate through the motor section to cool the motor parts and lubricate the bearings.
Seals and bearings are prone to failure due to continuous mechanical wear during operation of the pump. Mechanical rub between the stator and the rotor can generate particles. Interacting forces between the rotor and the stator in fluid seals and hydrodynamic behavior of journal bearings can lead to self-excited vibrations which may ultimately damage or even destroy rotating machinery. The bearings are also prone to failure. Lubricants can be rendered ineffective due to particulate contamination of the lubricant, which could adversely affect pump operation. Lubricants can also dissolve in the fluid being pumped and contaminate the fluid. Bearings operating in a contaminated lubricant exhibit a higher initial rate of wear than those not running in a contaminated lubricant. The bearings and the seals may be particularly susceptible to failure when in contact with certain chemistry. Alternatively, the bearings may damage the fluid being pumped.
What is needed is an improved brushless compact canned pump assembly design that substantially reduces particle generation and contamination, while rotating at high speeds and operating at supercritical temperatures and pressures.