Centrifuge and Rotor Safety Guide


Balancing a Load in a Centrifuge

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.


Purchasing an Autoclave

Purchasing an Autoclave

When you are looking for an autoclave the purchasing process can be overwhelming as they seem so complex which can result in  a very expensive mistake if you purchase the wrong unit

There are so many makes and models to choose from and so many options

Here are some helpful hints

The autoclave itself

  1. The size of the autoclave
  2. Load size

What is your load size, how many cycles per day/ week?  Remember  with circular chambers you cannot fit as much in as square chambers. Are you autoclaving animal cages – you will fit more cages in a square chamber. How many media bottles can you fit in one load?

1. The available space in your lab.

In other words, throughput capacity dictates the size autoclave you need, while floor space  determines what you can actually accommodate. Common sizes range from tabletop autoclaves to small, medium, large (bulk) and pass through autoclaves.  Remember to factor in the size of the autoclave when the door is open, enough room for airflow and  enough access for the service technician.

2. What types of loads will you be running in your autoclave?

The autoclave you purchase should possess the cycles capable of sterilizing your specific loads     media, glassware, biohazard bags, tips, porous loads, animal cages  or waste?  Be sure to enquire about which cycles your autoclave is capable of running and ensure your desired materials can be properly sterilized.   Depending on what your autoclaving you may require  options like vacuum. Air-ballast and load sensing probe.

3. Cycle data

a) How do you want to collect the cycle data? Paper, USB or ethernet ( to computer) or a combination of all three
b) Is the Touch screen ‘ User friendly”. Is there a security locking system on it so that lab staff cannot alter the cycles
c) How many cycles are stored in the history on the touch screen and can you reprint these?
d) How many cycles can you have and can you name them yourself?
e) Can you add or alter a cycle or do you have to pay for a service technician to do this? Cost can be $150 per hr plus expenses


4. Automatic drain and fill?

For the smaller autoclaves you can have automatic drain and fill

5. What is my steam source for the autoclave?

There are three types of steam generation in autoclaves;

a) Heaters in chamber- the heating elements are situated in the chamber rather like the elements in your electric kettle

b) Integral steam generator- a steam generator built in as part of the autoclave

c) Inhouse steam- is your water supply sufficient and of good enough quality to supply the autoclave?

 6. Loading Cart

Do you want a loading cart?  They are good to have for H & S reasons especially if autoclaving large volumes of media 


Do you have the correct utilities  available for the autoclave?

a) Water- depending on your water quality you may need a water softener

b) Compressed air

c) Drain

d) Power- do you have 3 phase power available


a) How will I get the autoclave from the loading dock to its final resting place?

b) Will it fit into the lift if its going to be installed on a higher floor?

c) Do we need to make adjustments to any walls, doors or floors to install the autoclave?

d) Cost of decommissioning the existing autoclave?

e) Does the cost of the autoclave include all of the above?

Service, Preventative Maintenance and Training

a ) Service  and Preventative maintenance – Does the company offer a service and PM contract?

b) Is the maintenance team factory trained?

c) Warranty- what is the warranty and what does it include?

d) Is training available and what is the cost?

e) Where is the steriliser manufactured and how many years has the autoclave manufacturer been in business? How many autoclaves has the supplier sold in NZ?

f) Ask for references- speak to someone who has one of these autoclaves in their lab


For more information contact Acorn Scientific today.