A centrifuge is a piece of equipment, generally driven by an electric motor (but some older models are still spun with hand), that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration causes heavier particles to move out along the radial direction (the bottom of the tube). By the same token, lighter objects will tend to move to the top (of the tube; in the rotating picture, move to the centre).

In the picture shown, the rotating unit, called the rotor, has fixed holes drilled at an angle (to the vertical). Test tubes are placed in these slots and the rotor is spun. As the centrifugal force is in the horizontal plane and the tubes are fixed at an angle, the particles have to travel only a little distance before they hit the wall and drop down to the bottom. These angle rotors are very popular in the lab for routine use.

Problem Solving[]

A centrifuge most common problem during preventive maintenance is the replacement of motor brushes. These brushes should be inspected or replaced as required by the manufacturers recommendation intervals E.g. On a routine PM inspection, we use a photo tachometer to measure the speed of the centrifuge. The meter reads 2000 RPM and on the next PM inspection the meter reads 500. This is indicative of worn or bad bushes that require replacement.

Performance Checks[]

  • Brushes
  • Safety interlock
  • Knobs
  • Timer Accuracy
  • Rotor
  • Maximum Speed
  • Temperature for refrigerated centrifuges