In a variety of machinery, working members are driven by hydraulic cylinders. Such hydraulic systems are used to control multiple functions, such as raising and lowering the member, tilting and rotating the member about an axis, and sliding the member fore and aft. Flow-control valves are used in these hydraulic systems to control rate of flow from one part of the system to another. A proportional-priority-pressure compensating type of flow-control valve is used to proportionally divide the pump flow between the branches of the circuit based on their requirement. The valve uses a pressure compensator for accurate flow rate control. The pressure compensator maintains a constant pressure drop across the main spool valve. The pressure compensator is an integral part of the flow-control valve. In this thesis, a model and stability analysis for the pressure compensator is presented.

Two water-pressure-compensated breathing devices for prolonged immersion have been designed, fabricated, and tested underwater. One valve is a continuous-flow regulator and the other is a demand regulator. Both valves allow exhalation through a hose directly into the surface atmosphere for air analysis. One of the two valves has been used extensively during prolonged weightlessness simulation tests by immersion.

Fluid Power Circuits and Controls: Fundamentals and Applications, Second Edition, is designed for a first course in fluid power for undergraduate engineering students. After an introduction to the design and function of components, students apply what they’ve learned and consider how the component operating characteristics interact with the rest of the circuit. The Second Edition offers many new worked examples and additional exercises and problems in each chapter. Half of these new problems involve the basic analysis of specific elements, and the rest are design-oriented, emphasizing the analysis of system performance. The envisioned course does not require a controls course as a prerequisite; however, it does lay a foundation for understanding the extraordinary productivity and accuracy that can be achieved when control engineers and fluid power engineers work as a team on a fluid power design problem. A complete solutions manual is available for qualified adopting instructors.

The excitement and the glitz of mechatronics has shifted the engineering community's attention away from fluid power systems in recent years. However, fluid power still remains advantageous in many applications compared to electrical or mechanical power transmission methods. Designers are left with few practical resources to help in the design and

This thesis deals with innovative working hydraulic systems for mobile machines. Flow control systems are studied as an alternative to load sensing. The fundamental difference is that the pump is controlled based on the operator’s command signals rather than feedback signals from the loads. This control approach enables higher energy efficiency and there is no load pressure feedback causing stability issues. Experimental results show a reduced pump pressure margin and energy saving potential for a wheel loader application. The damping contribution from the inlet and outlet orifice in directional valves is studied. Design rules are developed and verified by experiments. A novel system architecture is proposed where flow control, load sensing and open-centre are merged into a generalized system description. The proposed system is configurable and the operator can realize the characteristics of any of the standard systems without compromising energy efficiency. This can be done non-discretely on-the-fly. Experiments show that it is possible to avoid unnecessary energy losses while improving system response and increasing stability margins compared to load sensing. Static and dynamic differences between different control modes are also demonstrated experimentally.