1. Laboratory instruments
Lecture (2)

2. Basic components of centrifuges
1. Central Shaft:
It is a part that rotates when spinning is effected manually.
2. Head:
It is a part that holds the bucket and connected directly to the central shaft or spindle.
3. Bucket or tube:
Are portions that hold test tubes containing a given sample to be spined.

3. Classifications of centrifuges
(1) Hand centrifuges
These centrifuges are:
Operated by hand or water pressure and they are most commonly used in small laboratory for routine purposes, used for preparation of urinary sediments and to concentrate parasites from the given specimen
Not advisable to use them to separate serum from whole blood.
They are fixed type.

4. (2) Electrical Centrifuges
Electrical centrifuges are those centrifuges that are operated by electrical power and produce high centrifugal force.
They are used in most medical laboratories. Based on their tube angle rotation, there are two types; Swing out head and Fixed head.

5. Kinds of centrifuges Micro-centrifuges:
They are used for spinning small tubes as in blood bank laboratories.
2. Medium size centrifuges:
Are used for centrifuging of urine specimens for microscopic analysis of urinary sediments.

6. 3. Large centrifuges
They are widely applied in bacteriology and medical chemistry laboratories.
A centrifuge may have a preset speed or more often there is a knob by which the laboratory personnel control the speed.
The speed is given in revolution per minuets (rpm). small models are designed to centrifuge volumes up to 200 ml at maximum speeds of 3, ,000 rpm.
Large models will centrifuge volumes up to 2,200 ml with maximum speeds of 5,000 rpm.

7. Types of centrifuge There are at least five types of centrifuge:
preparative centrifuge
analytical centrifuge
angle fixed centrifuge
swing head centrifuge
haematocrit centrifuge

8. Types of rotor Fixed-angle rotor
The rotor (mainly made of aluminium) is very compact.
There are bore-holes with a specific angle (like 45°) within the rotor.
These bore-holes are used for the sample tubes.

9. Swing-out rotor The rotor looks like a cross with bucket.
Within these buckets, different tubes can be centrifuged.
For a safe centrifugation, a specific adapter for every tube shape is mandatory.

10. The rotor is closed by a rotor lid.
The rotor is located in a rotor chamber which is covered by a metal centrifuge lid.
The open lid prevents the motor from turning the rotor when the rotor chamber is open.
During the run, the lid is locked.
The lid protects the user from being injured by touching a rapidly spinning rotor.
The rotor chamber and the lid of high quality centrifuges are robust enough to survive a rotor failure at full speed.

12. Use and care of centrifuges
1. Reading the manufacturer’s instructions.
2. Placing a centrifuge on a firm level bench out of direct sunlight, towards the back of the bench.
3. Whenever possible using plastic tubes made from polystyrene or autoclavable.

13. 4. Always closing the centrifuge top before turning it on.
5. Always balancing the tubes that are being centrifuged.
Tubes of the same weight should be placed directly opposite to each other.
Tubes should also be of the same size and should also contain the same amount of liquid.

14. 6. Increasing spinning speed gradually is important.
That is if you are required to spine a mixture at 3, 000 rpm, first put the dial on 1,000 rpm.
Give the centrifuge a chance to come up to that speed, then turn up the dial a little further until it reaches the desired 3,000 rpm.
Five minutes are the usual time required to centrifuge most substances.

15. 7. Never open the centrifuge while it is still spinning.
Never try to slow it down with your hand.
Most centrifuges have a brake, which will cause the centrifuge to stop faster.

16. Emergency lid release
In case of power failure or any malfunction, the lid can be opened manually to protect your samples.
Proceed as follows:
- Switch off the centrifuge and unplug the power cord.
- There is a plastic plug at the left side of the centrifuge housing. Behind that plastic plug there is a red cord.
- Remove the plastic plug and pull the red cord. The lid can then be opened