INTRODUCTION The primary purpose of the sixth edition ofFluid Power with Applicationsremains the same as that of the previous editions: to provide the student with in-depth explanation of the vast field of fluid power. As such, this book covers all subjects essential to understanding the design, analysis, operation, maintenance, and application of fluid power systems. It is written for associate and bachelor's degree candidates studying technology at community colleges, technical colleges, and four-year colleges and universities. In keeping with the previous editions, theory is presented where necessary, but the emphasis is on understanding how fluid power systems operate and on practical applications. The student then learns not only the "why" but also the "how" of fluid power systems operation. NEW IN THE SIXTH EDITION Based on input from users of the fifth edition and from my colleagues, the following changes have been incorporated into this book. Material on ancillary hydraulic devices (such as reservoirs, accumulators, pressure intensifiers, seals, heat exchangers, pressure gauges, and flowmeters) has been removed from various chapters and combined into a new Chapter 11. As a result the chapters dealing with major components, such as pumps, cylinders, motors, and valves, are more coherent and focused, resulting in enhanced read ability and understanding.

Many of the example problems and end-of-chapter exercises have been changed to better reflect current industrial applications. The example problems and exercises encompass a wide range of subject matter and levels of difficulty to allow students to progress in an orderly manner. Section 8.6 has been added to include coverage on proportional control valves. It has become increasingly more important to discuss the operation and application of these solenoid-operated valves because they provide precise, dependable, variable speed control of cylinders and motors in open-loop fluid power systems. A number of photographs and illustrations have been updated to reflect current fluid power technology. These include programmable logic controllers, microprocessors, and electrohydraulic servo systems. Section 12.

11, on fluid cleanliness levels, has been added. The basis for controlling particle contamination of hydraulic fluid is to measure they fluid's cleanliness level. It is important to present this subject, because manufacturers of hydraulic equipment specify the fluid cleanliness levels required for providing the; expected life of their components. Derivations of key equations have been removed from various chapters and combined into a new Appendix I. This change allows students to better concentrate on applications without undue emphasis on mathematical analysis. This is especially valuable in early chapters where understanding the operation off fluid power components can be more difficult because of the simultaneous inclusion of mathematical theory. Appendix I should be used by instructors who want to pay more attention to teaching students how equations are derived. A new Section 13.

6 includes material on the analysis of moisture removal from air. Moisture in the air delivered by a compressor washes away lubricants, causing excessive wear in components such as cylinders, valves, and motors that contain moving parts. Moisture also causes metallic surfaces to rust, thus damaging plumbing components such as conductors and fittings. It is therefore; important to know how to determine and reduce the rate at which moisture enters a pneumatic system. Material on hydraulic cylinders and hydraulic motors (previously covered in a single chapter) has been rewritten and placed into two separate chapters for better clarity and focus. Chapter 6 is devoted to hydraulic cylinders, and Chapter7 concentrates on hydraulic motors. This change allows readers to obtain a better understanding.