scope:

This European Standard specifies a method for assessing the oxidation stability of phosphate ester hydraulic fluids. These products fall into category HFDR of EN ISO 6743-4 [2] and into categories TSD, TGD and TCD of ISO 6743-5 [3]. The amount of acid developed during the test and the mass changes of the metal specimens are used to assess the level of oxidation stability. The precision of the test method applies to changes in acid number up to 3,0 mg KOH/g and changes in mass of up to 3 mg per test piece. The change of acidity is determined using one of the test methods ISO 6618, ISO 6619, or ISO 7537. Results from two different test methods are not necessarily compatible and direct comparison needs caution.