This book was developed to instruct people who want to troubleshoot hydraulic machinery and hydraulic circuits. The book's material assumes no prior knowledge of hydraulics and could be used by anyone who has an interest in this particular area of fluid power. This book does not cover the rebuilding of hydraulic components. In order to firmly plant the concepts of what is going on in hydraulics, this information has an orientation to a "hands-on" approach. The text uses some generalizations and other approximations, and is directed at the hourly worker on the factory floor or out in the field.