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Balancing a Load in a Centrifuge

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When balancing a centrifuge you should  follow some simple rules:

  1. You must never be run a centrifuge with buckets missing, although opposing buckets may be left empty.
  2. All opposing loads must balance within a certain weight as specified by the centrifuge manufacturer’s instruction manual.
  3. If opposing buckets are run with a partial load of tubes in their adapters, these tubes must be arranged symmetrically, both with respect to the pivotal axis of each bucket and across the centre of rotation (see Figure 3). With some partial loads, you may not have an equal amount of tubes with the correct liquid height in them. The simplest solution is to fill one or more tubes of the same size with water, or a denser liquid if necessary, and use them to balance the load symmetrically.

 

Most centrifuges are equipped with an imbalance detector which turns the centrifuge off before any eccentric rotation caused by a load imbalance can damage the drive shaft or bearings.

Please note that an improper distribution of tubes in carriers or adapters can cause poor separations even if the imbalance isn’t severe enough to trigger this detector. In these situations, the buckets won’t pivot to the required horizontal position during the run, resulting in poor density separations or re-mixing of  the sedimented material during deceleration.

Also, the possibility of tube breakage during the run is greatly increased when the buckets are not horizontal at operating speed. You may notice that the centrifuge vibrates when the rotor is accelerating or decelerating at low speeds. This is normal, and occurs as the rotor  passes through a so called critical speed range where any small vibrations are temporarily amplified.

Your separations will not be disturbed during deceleration, because the centrifugal force is still high enough to stabilize them.

 

For more information, contact Acorn Scientific today.

 

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  • Jackie Anderson