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Combine 25 years of electrohydraulic component, production, and system experience with control theory into a new valve design incorporating both nozzle-flapper and solenoid components, and you obtain an innovative, differential pressure control pilot valve (PCP). Utilizing a single component that integrates many functions, this invention reduces a complicated valve into a simple low-cost assembly, yielding a multi-purpose (patent-pending) electrohydraulic servovalve. This PCP has been combined with several patented boost stages to yield pressure control servovalves (PCS) and flow control servovalves (FCS) that can be utilized in construction, industrial, and agricultural environments. The new, simplified and symmetric PCP/PCS can drive a pump directly with an option of built-in electronic rotational feedback. The PCP generates servovalve performance at less than proportional valve costs. These controls can be utilized in both open and closed-circuit arrangements.

A family of cost-effective, high performance, electro-hydraulic servovalves has been developed for mobile and industrial machinery applications. The development was motivated by cost pressures on mobile and industrial closed loop servo system applications. The servovalve consists of a closed loop, pressure control pilot stage valve mated with a unique double spool design boost stage valve. It has been configured in both a flow control version and a pressure control servovalve version. Operating principles, performance characteristics, and general application are described.

Extending proportional valves into higher response and closed loop applications without cost penalties is highly desire-able. Pressure control servovalves can be used to enhance proportional valves in open loop applications and flow control servovalves can be adaptive to open and closed loop applications where higher response and better accuracy is required. A new line of electrohydraulic valves has allowed a cost effective approach to obtain this goal of servovalves at electrified proportional valve costs. System applications are shown to demonstrate the valve's (and controller's) cost and performance advantages in closed loop operation.