Soda Acid Extinguisher
This is a typical type-A fire extinguisher. A 9 liter cylindrical shaped Soda extinguisher is shown in the figure.The outer shell of the cylindrical shape body is made of steel. The end of the shells are flattened, dished and then welded or riveted to a wrapper plate.
The shell of these type of extinguishers are capable of withstanding pressures upto14 bars even if there is a resistance in the discharge nozzle.
Near the neck of the extinguisher is a small glass phial which contains sulphuric acid. The outer container contains alkaline sodium bicarbonate solution. The rest of the body is filled with water. The shell and the casings are hydraulically tested before the installation. It is to be noted that the extinguished is to be operated only in the upright position.
In order to operate the extinguisher, the pin at the top of the extinguisher which is attached to the sulphuric acid glass phial inside the extinguisher, is pushed. This breaks the glass phial, which results in the mixture of sulphuric acid and sodium bicarbonate. The chemical reaction between the acid and the alkali, leads to the formation of the carbon dioxide. This highly pressurized carbon dioxide pushes the water out of the discharge. The discharged water contains residue of chemical reaction.
Refilling of extinguisher is done once in an year, if it is not used. Chemicals (or chemical kits) are available in sealed bottles for recharging. A small screwed brass cap is examined in order to check the cap seal and the small holes in the sides. The holes are used to release any internal pressure before the cap is removed. The ball valve fitted below the plunger is checked in order to prevent the liquid rising into the internal pipe.