Methods and mechanisms of liquid mixing have received only limited research and development, yet mixing is one of the most common operations in the chemical industry. Most of these investigations have been into mechanical devices with few studies being made of other methods.

The development of electrohydraulic floating-disc valves at the University of Surrey started in the early 1980's. The progress in the last ten years since then has shown that floating-disc valves have the advantages of fast response time, reliable operation, simple configurations, few critical dimensions with no precision sliding surfaces, leading to low cost design and manufacture. They have great potential to fill the gap between conventional solenoid valves and high precision servo valves. However, limitations existed in previous designs hindering further development; for instance relatively large moving mass, low hydraulic stiffness, difficulty of installing springs and poor null position when operating in proportional control mode. The work presented in this thesis concentrates on improving the disc valve electromagnetic characteristics, hydraulic stiffness, electric power consumption, operating reliability, valve size and cost. A novel diaphragm-disc force motor has been successfully developed through this research. The theoretical study and experimental work has shown that the force motor has the features of high spring stiffness, fast response, improved accuracy and linearity, and miniaturised size. By implementing a pair of permanent ring magnets, the diaphragm-disc force motor also has the advantages of lower electric power consumption, dual-lane for fail safety operation, and higher control accuracy. Due to the use of conventional mild steel instead of Remco B soft iron as the coil magnetic conductor material, the valve manufacturing cost has been further reduced. Above all, this novel configuration shows good prospects of competing with the existing torque motor due to its low cost and simple construction. The research described also involves designing and testing two prototype disc valves for specific applications. A single disc pilot valve associated with the diaphragm configuration and permanent magnet arrangement has been built for use in an aviation engine fuel supply system. It has a dual-lane operating mode with a valve size of 58x50x50 millimetres, which is the smallest valve yet made in the disc valve family. The initial test results showed that the valve has good linearity and a bandwidth of 60 Hz in a blocked-load condition. Another successfully built valve is an improved version of a position controlled double-disc valve for use in vehicle semi-active suspension systems. It has been demonstrated that using proportional plus derivative electronic network compensation, the valve can operate continually in the whole damper control domain with the characteristics of balanced fluid forces and low electric power consumption.

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This thesis presents the design, simulation and real time implementation of control strategies of a subsea multiphase electric pump system, which consists of a pair of piston type pumps, a permanent magnet linear synchronous motor (PLSM) , a voltage source inverter and a control unit. The pump is required to operate efficiently and effectively for pure oil, pure gas, and for a mixture of the two.

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