Manual of basic techniques for a health laboratory - libdoc.who.int

72 Manual of basic techniques for a health laboratoryInstalling the centrifugeThe centrifuge must be placed on rubber pads or a mat on a flatlevel surface.Fig. 3.41 Balancing centrifuge tubesBalancing the tubesIf the tubes are numbered, place them as shown in Fig. 3.41:— tube 1 opposite tube 2;— tube 3 opposite tube 4.Balance the tubes that are opposite each other by weighing themin their buckets on the open two-pan balance.Fig. 3.42 Balancing centrifuge tubes by addingliquid to the lighter tubeFig. 3.43 Balancing centrifuge tubes by adding water tothe bucket containing the lighter tubeTo balance: either add more of the liquid to be centrifuged to the lighter tube (Fig.3.42); or add water to the bucket containing the lighter tube (using a wash bottle;Fig. 3.43).If only one tube of liquid is to be centrifuged, balance it with an identical tube filledwith water.Preventing breakage of tubesAlways pad the bottom of the buckets with the rubber cushions provided with themachine. This protects the bottom of the centrifuge tubes.Using a wash bottle, add a little water between each tube and its bucket.Safety precautions● Check that the tubes are the correct size for the centrifuge. Tubes that are toolong or too small may break.● Fill the tubes to no more than three-quarters full to prevent spillage in the bowl.● Always balance the centrifuge buckets before starting the centrifuge. Failure todo this can cause excessive wear or the centrifuge may move.● Ensure that the lid is closed before starting the centrifuge.● When starting the centrifuge, gradually increase the speed, turning the knobslowly, until the desired speed is reached.● Stop the centrifuge gradually (some models have a brake that can be applied).Never try to slow the centrifuge down with your hand.● Never open the centrifuge until it has come to a complete stop.● Remove the tubes slowly and carefully.