Balancing your centrifuge

The centrifuge works using the sedimentation principle, where the centripetal acceleration causes more dense substances to separate out along the radial direction while the lighter objects will tend to move to the top.  The G force attributed to each tube in the centrifuge can change drastically even with a small weigh imbalance when the centrifuge rotor is spinning at high RPMs.  Imbalanced rotors can create excessive vibration which will affect the performance separation and cause damage to your centrifuge and your safety.  Properly balance your centrifuge will ensure optimal performance and longevity of your centrifuge and your safety.
The principle of centrifuge balancing is to make sure that the center of gravity is located on the center of the rotor.  When even numbers of tubes are loaded (assuming that all tubes are the same weight), placing a sample tube on opposite side of another sample tube will put the center of gravity on the center.   When an odd number of tubes are loaded, a balance tube can be loaded in tube holder opposite to the last sample tube.

For twelve placement or twenty placement rotors, odd number of sample tubes can be loaded without using a balance tube because the number of tube holders is divisible by three.  First, Load three sample tubes with equal spacing (every four tube holders for twelve tube rotor or every eight tube holders for twenty four tube rotor).  Then load the rest of the even sample tubes on the opposite to each pair of sample tubes.  Using this method, three or five samples tubes can be loaded on the rotor without using a balance tube as the illustrated below.