Rotors and Their Uses

The two main types of rotors used in laboratory centrifuges: swingout  bucket ( horizontal ) and fixed angle.

Swing out rotors or horizontal rotors are so-called because the buckets or racks which hold the centrifuge tubes are suspended in a manner which allows them to swing up into the horizontal plane when being centrifuged.  This allows them to swing up into the horizontal plane when being centrifuged. Thus, when the centrifuge is operating, particles sediment along an unimpeded, radial path, away from the centre of rotation, and deposit evenly on the bottom of the tube or other container. The flat upper surface of the sedimented material makes it easy to remove the   supernatant from a loosely packed pellet. By means of various adapters, more than one type or size of tube can be centrifuged together, provided the load is properly balanced.  

Fixed angle rotors hold the tubes  in a fixed position at an angle to the axis of rotation. The angle varies with different rotors, somewhere between 25°C to 40°C.  Although particles sediment along a radial path in these rotors also, they soon strike the opposite side of the tube where they  slide down the wall to the bottom. This results in a faster sedimentation than  that of swing out  rotors which have a longer sedimentation pathlength. But because the bottom of the tube is not aligned with the direction of the centrifugal force, particles will collect partly along the side of the tube. This can make the collection of a loosely packed pellet more difficult than when a swing out  rotor is used.

These  two categories of rotors, offer  models with different combinations of capacity and maximum RCF attainable. Swing out rotors, in particular, give you the flexibility to centrifuge a variety of tube sizes right up to large containers and blood bags. Swing out rotors can also be equipped with racks or carriers, rather than buckets, suitable for spinning RIA tubes or micro-test plates.

When quick pelleting of small particles is required, fixed angle rotors should be used and because of their design, these rotors are capable of higher speeds. Sedimentation of larger particles, such as cells, protein precipitates, antigen-adsorbent complexes, urinary crystal, etc., can be done at lower speeds with swing out rotors.

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