Atmospheric oxygen reacts constantly with oils producing organic oxidation products that are acidic in nature. This reaction is very slow at ambient temperature and has little effect upon oil conditions.
At temperatures that will develop within a running engine, reaction rates are much increased. This happens at an even higher rate when localised heating occurs on sliding surfaces, as the temperatures can be much higher than that of the surrounding material. Combustion and wear products in solution may additionally speed up the reaction between the oil and oxygen. The result of this process are degradation products which are organic acids. They do not react easily with the alkaline AN additives and therefore tend to co-exist. As a result oil viscosity increases and lacquers can deposit on hot surfaces.
Acid Number oil analysis or AN as a result gives the user both the weak organic and strong inorganic acids present in the oil as total acid number. It is applicable to gearbox, gas engine, gas turbine and hydraulic lubricants. Acid Number oil analysis (AN) is not generally associated with engine crankcase lubricants unless they are severely contaminated. The singular exception to this may be crankcase lubricants for gas engines. In this instance, AN can deplete very rapidly and elevated operating temperatures can generate high levels of weak organic acids.

Acid Number Testing Products

Acid Number Drop Test Kit - The AN Drop Test Kit comes complete with all necessary reagents and equipment for a fully portable Acid number test. The test is based on a chemical titration test. Drop by drop is added from a dropper bottle into a test jar. The number of drops do represent the AN number of the oil.

Electronic Acid Number Test Kit - gives highest accuracy in the same measuring range.

Replacement reagents can be ordered at short notice. Reagents are ready in packs. AN Reagent pack available with all needed for 25 Tests. The AN reagents are classified as hazardous for transport. (UN1993, UN1170)