How Improper Centrifuge Rotor Balancing Can Damage Your Centrifuge

Since the invention of the centrifuge in the 19th century, hazards caused by rotor imbalance have always existed. In mild cases, it causes wear on the machine shaft and shortens the service life of the centrifuge; in severe cases, it may lead to personal injury and casualties.

Once a high-speed rotating rotor breaks out of the chamber, it turns into a sharp flying blade in seconds, bringing extreme destructive harm.

So how to avoid the risks caused by rotor imbalance? The best solution is to master the correct balancing method, and today we’ll give you a simple explanation!

1.Fixed-angle rotor balancing

For the balancing of fixed-angle rotors, it is usually sufficient to keep the central symmetry method in mind.Taking the balancing of the 12-hole fixed-angle rotor shown in the figure below as an example, samples can be placed following this principle:

2.Swing-out Rotor Balancing

In practical applications, balancing swing-out rotors is the biggest headache for lab personnel. It is necessary to not only consider the symmetry of centrifuge tubes within a single basket, but also ensure balance with the centrifuge tubes in the opposite basket.

Two key principles must be kept in mind during balancing:

1.When placing centrifuge tubes in a single basket, ensure the basket’s center of gravity aligns with its central point.

2.When arranging tubes in the opposite basket, take the placement of the first basket as the reference, and position the tubes strictly following the central symmetry principle of the rotor.

Taking the balancing of a 4×14-hole swing-out basket rotor shown in the figure below as an example, samples can be placed in accordance with the above principles.

3.Balancing for an Odd Number of Tubes

In addition, it is quite common to encounter the scenario of balancing an odd number of centrifuge tubes. Most researchers usually place a blank balance tube filled with water in such cases. This method is simple and easy to operate. However, it becomes rather cumbersome for frequent centrifugation experiments where the mass and volume of samples often vary.

So how exactly should we balance the rotor in this case?

Take a 24-hole fixed-angle rotor as an example. The operation can be divided into three scenarios:

 1. When there is only 1 tubeor 23 tubes, there is no alternative but to prepare one tube filled with water for balancing.

 2. Triple balancing method: When the number of centrifuge tubes is a multiple of 3 (such as 3, 6, 9, 15, 21, etc.), place the tubes clockwise with reference to the figure below.

3. Double-plus-Triple Balancing Method: For 5, 7, 11, 13, 17 or 19 centrifuge tubes, follow the principle of central symmetry. First balance 3 tubes, then balance another 2 tubes. The overall combination will remain balanced in the end.

Ultimately, centrifuge rotor balancing hinges on the principle of symmetry. The relative mass of two centrifuge tube cups on the same moment arm must be kept equal.In practical operation, place tubes into the rotor holes gradually following the combination rule of 2+2+2…+3. As long as each group is kept balanced, the overall balancing effect can be guaranteed perfectly.

The intuitive diagram below illustrates this principle more clearly and straightforwardly.

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