The various properties of hydraulic fluids outlined in the previous chapter are qualified and quantified by standard tests. Along with many other institutions, the American Society for Testing and Materials (ASTM), the Deutsches Institut fur Normung (DIN) and the Institute of Petroleum (IP), U.K., did pioneering work in formulating test standards for petroleum products. This has helped lubricant manufacturers as well as users to maintain and enhance the quality of lubricants over the years. If it weren't for the test standards, the performance of hydraulic fluids or lubricants would not have reached today's high level. For readers, the tests described here will give a better insight into the technology of making high-performance hydraulic fluids, and will help them understand the various specifications of hydraulic oils. Also, when confronted with a problem, this knowledge will help readers identify the kind of tests to be carried out in order to diagnose and solve the problem. Formulating test standards is a dynamic process, and as such they are always under periodic scrutiny and are revised when necessary. Not only old standards are revised or withdrawn, but new performance criteria are also added.
The test procedures described here are based on ASTM standards  unless otherwise specified. Tests are always conducted under specific conditions, which usually involve elaborate preparation of test apparatus and test samples. Those are not described here and readers may refer to the relevant standard for details. The list of test standards and the numbers for various national standards are given in Table 3—1. The table gives only the equivalent standards; these standards are not necessarily identical to one another, and there could be variations in the test procedure and test conditions from one national standard to the next. Hence, when comparisons are made, caution must be exercised—test parameters, test conditions, and methods of measurement must be taken into account.