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This paper investigates two well known parameter estimation techniques, the ordinary least squares and the maximum likelihood methods, for parameter estimation in the main spool of a solenoid proportional valve. The methods are relatively easy to apply and are applied in two steps. The first step consists of operation with closed outlet ports. This eliminates flow forces on the spool enabling the spring constant and precompression to be estimated. These values are then used in the next step, which is the open port case, to estimate valve orifice area gradient and dead band. The results agreed quite well with experimental values determined using a graphical technique for spring constant and pre-compression. However, estimations of the dead band and orifice area gradient showed a strong temperature dependency, contrary to physical expectation.

The development of high precision flow divider/combiner valves has received considerable attention by the authors over the past decade. Several different valve designs for division and combination of flow have been designed which display small flow dividing/combining error (1-2%) when compared to conventional designs (2-10%). Recent studies have improved upon the design in order to reduce cost, weight and complexity of the valve. This paper will present the latest of the authors research into the development of a high precision, autoregulated flow divider/combiner valve with an integral shuttle valve. The autoregulator extends the operating range of the integrated flow divider/combiner valve (for errors less than 2 %) to 10-50 lpm compared to 30-50 lpm for the unregulated valve.

A flow divider valve is a device which allows a single stream of fluid to be split into two paths according to a predetermined ratio and independent of variations or differences in the load pressures. A flow combiner valve combines two paths of fluid into one stream such that the ratio of the flow rates coming into the valve remains independent of any variation or difference between the inlet pressures. This paper describes the design, operation and performance of an integrated flow divider/combiner valve. This design maintains the small flow dividing/combining error of high precision valves (less than 1.5% at rated flow) but incorporates the shuttle valve into the main spool system. This new design reduces the weight of the valve by 20% reducing the cost by approximately 10%. The new structure simplifies the construction of high precision valves and reduces a source of flow dividing/combining error (leakage).