Bearingless Pump Technology

 

A New Standard for Magnetically Levitated Centrifugal Pumps
Levitronix has developed a Bearingless Centrifugal Pump based on proprietary magnetic levitation technology. With the Levitronix technology, a pump rotor is suspended and driven by the magnetic field of a motor/bearing stator through the wall of the pump housing without mechanical contact. A signal processor-based electronic control unit allows precise regulation of the speed, pressure or flow rate.

The Levitronix BPS pump systems are designed for high-purity fluid applications where low particle shedding and metal contamination are required. The pump heads are made from high-purity fluorocarbon resins (PTFE, PFA, ECTFE, PVDF) and can be easily cleaned or exchanged resulting in less down time and lower maintenance costs.

A simple and compact solution for a centrifugal pump is feasible with our bearingless motor concept. Figure 1 shows the basic arrangement of a bearingless slice motor pump. The Levitronix pump is comprised of a single motor/bearing unit that provides both drive and magnetic bearing functions simultaneously. This design is capable of magnetically stabilizing six special degrees of freedom of the impeller in a contact-free manner through the walls of the pump housing. Compared to conventional canned motor pumps, significantly larger magnetic gaps are possible, and there is more room for canning between the rotor and the motor stator. The canning may be fabricated from a variety of different materials which form the pump housing. This results in a simple design for the pump that is comprised of only three parts: an impeller that contains an over-moulded magnet ring, a bottom casing and a top casing. The pump head can be easily detached from the motor/bearing stator and cleaned without difficulty. In certain applications, such as in blood pumps, the pump head can be produced as a disposable unit (Figure 2). Levitronixpumps have been designed for many different applications in different sizes and materials. Figure 3 shows the design of an implantable Ventricular Assist Device (VAD) which has been jointly developed in collaboration with Thoratec Corporation. Figure 4 shows Bearingless PTFE pumps for ultra pure liquid transfer in Semiconductor Manufacturing.

Features and Benefits
The bearingless canned motor pump has several outstanding features due to its unique construction. Simply stated, this design embodies all of the advantages of conventional canned motors or magnetic coupling pumps while avoiding problems related to lubricated bearings. There are no narrow gaps or fissures and the pumps do not generate any particles. These pumps can be operated with critical fluids such as blood, ultra pure chemicals, and CMP slurries. Since there is no mechanical coupling between the impeller and pump housing, the pump produces no vibration, even if there is significant imbalance in the impeller (i.e. if solids adhere to the impeller). Thus, bearingless pumps are silent. Noise due to turbulence can only be heard at high flows. The absence of mechanical contact between rotating and stationary parts leads to a virtually wear-free product. Wear is limited to the pump head if is operated for extended periods with abrasive or aggressive chemicals. Should it become necessary, the pump head can be easily exchanged within a few minutes depending on the type of mountings and fittings.

In addition, variable speed operation of the Levitronix pump allows precise control of flow or pressure over a wide operating range. An entire range of conventional fixed frequency pumps can be replaced by a single Levitronix pump. High operating speeds (up to 10,000 rpm) are possible by eliminating the bearings, using metal cans and utilizing wide gaps and small motor surfaces. Therefore, high pressures can be achieved with only one stage. As an example, 6 bar (87 psi) is feasible with an impeller diameter of only 65 mm. This feature permits Levitronix to build smaller pumps compared to fixed speed pumps of the same power.

The benefits of the Levitronix pump can be divided into three categories as summarized below:

Canned motor design

  • No rotating seals so the system remains self-contained

Magnetic levitation of the impeller

  • No wear resulting in reduced downtime and low maintenance cost
  • No lubrication required plus the capability of running dry
  • No particle generation
  • Wide clearances between the pump casing and impeller, and therefore, no clotting or stopping of the pump
  • Simple cleaning, steralization, and exchange of the pump casing and/or impeller
  • Wide temperature range
  • Extremely low vibration and noise

Electronic speed control

  • Precise control of flow rate or pressure
  • Flow and pressure control without throttle valves enabling high system efficiency
  • Continuous or pulsating flow by control
  • High pressure from a single stage pump
  • Extremely small in size compared to diaphragm and bellow pumps