Why is my centrifuge imbalanced? Solving the imbalanced centrifuge problem

An imbalanced centrifuge is a common fault that is encountered by many lab users. A centrifuge can display the dreaded ‘out of balance’ error message. This forces the instrument to abort its run and stop the rotor from spinning. This can be very annoying when you have time-sensitive samples that need to be centrifuged.

In this month’s blog, we examine what causes the imbalanced centrifuge problem and how you can solve it. Let’s take a closer look:

Some simple checks and fixes you can perform on an imbalanced centrifuge

Loading the rotor properly

The main cause of an imbalanced centrifuge is usually because the rotor is unevenly loaded. Buckets must be loaded symetrically and the tubes or containers should be distributed evenly on all rotor positions. Below is a good illustration of this:

You should also always run the centrifuge with a full set of buckets and each bucket should weigh the same +/- 5 grams. It is best practice to have a set of digital laboratory scales near the centrifuge to ensure the loaded buckets all weigh the same.

In addition to this, you should try to spin the same types of tubes and containers in each run and of course, always follow the manufacturer’s instructions.

Firmly attach the rotor to the motor shaft

Ensure that the rotor is firmly seated on the rotor shaft. Ensure that the rotor nut is securely fixed too. Some manufacturers supply you with a rotor spanner to tighten up the rotor nut. You don’t need to go overboard with tightening it because you may find it difficult to get the rotor off later, particularly when decontaminating. However, you should ensure that it is properly tightened up so that the rotor is secure.

Greasing the trunnions

It is also important that the trunnions, where the bucket sits, are adequately greased. A small amount of silicone grease should be smeared on the trunnions to prevent balance issues. If this is not done, then buckets can get stuck in one position during the centrifuge run. Thus, causing an imbalance issue. Your can get a small amount of silicone grease online from Amazon.

Check for a bent motor shaft

Another simple check that you can carry out it is slowly spinning the rotor round by hand to check for any irregular movement. It could be that the shaft of the motor is bent.  This can occur when the centrifuge has experienced a particularly violent imbalance issue, perhaps due to improper loading of the rotor. The shaking of the centrifuge with a fully loaded rotor can bend the motor shaft.

A bent motor shaft can cause the rotor to no longer spin in a perfect circle, which can in turn cause further imbalance issues. A bent motor shaft usually means a new motor is required and for this, you should contact your local centrifuge service provider.

Other causes of an imbalanced centrifuge

If all of the above does not solve your problem, then the issue could be buried deeper inside the centrifuge. It could be that the Anti-Vibration (AV) mounts under your motor have perished or the motor bearings themselves have gone. In order to rectify this, you will need a qualified technician to come out and assess the issue and repair it on-site.

It could also be that the micro-switch which triggers the out of balance has shifted. This can sometimes happen if the centrifuge has suffered a sudden jolt in transit. This is why some users open the box of their brand-new centrifuge, turn it on, only to find an imbalance error during its first use. If this happens to you, you should contact your local centrifuge repair specialist.

How Henderson Biomedical can help

Our company specialises in maintaining and repairing centrifuges of all makes and models. We have been doing this since 1987. Our team of engineers cover the whole of the UK and can rectify any issues you have with your centrifuge at your site. If you would like to discuss any technical issues you are experiencing with your centrifuge, please call us on 020 8663 4610 or you can contact us using our online form.