The high accuracy position servo system of pneumatic cylinder is already reported by using a diaphragm-type electro-pneumatic converter. In this paper, a novel simple high accuracy position servo system are shown by using high response solenoid valves. The actuating part consists only of two valves and a cylinder. The valves open or close by a pulsating signal and charge the air to the cylinder or discharge from the cylinder directly. The pulse time duration and interval change with position of piston and this is not same as the conventional PWM method. To realize high accuracy piston displacement, the interval becomes as short as 0.005 s when the piston approaches near by the desired point.
The characteristics of this servo system are given by using a system model, and the relationship between stability of the piston displacement and valve opening duration can be shown theoretically. The single rod-type cylinder with 40 mm bore and 100 mm stroke is tested experimentally. As a result of repeated positioning test, it was shown that the piston keeps moving slightly at the desired point but it is able to position within 0.01 mm to the point.

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A couple of cylindrical chokes in series are often used in hydraulic systems to obtain the same restrictive effect as a single choke with a fine inner diameter. These coupled chokes are advantageous due to their easy drilling and toughness regarding contamination. The mathematical model of the dynamics of cylindrical chokes have been established, however, the dynamic characteristics of these couple chokes have yet to be clarified.
An aim of this research is to investigate experimentally, the dynamic characteristics between the flow rate and pressure difference by making use of a cylindrical choke-type instantaneous flow meter, which has been proposed and developed recently by the authors.
The flow rate through the chokes is measured by the cylindrical choke-type instantaneous flow meter, consisting of the upstream side choke of the coupled chokes, a differential pressure transducer and a microcomputer system to estimate the unsteady flow rate in real time. The sampling frequency of the flow meter is set at 5.5 kHz. The pressure difference across the coupled chokes is measured by another differential pressure transducer and fetched to the system simultaneously. The frequency responses and step responses are examined experimentally.
As a result, it is confirmed that the dynamic characteristics are greatly influenced due to the existence of coaxial unsteady jet caused by an upstream choke and are quite different from those of independently connected choke characteristics without the existence of jet flow.
In addition, a simple mathematical model, including the influence due to the jet flow, is proposed and the theoretical results are in good agreement with the experimental results. It is also confirmed experimentally that the newly devised rectifiers set up in front of chokes are valid to avoid the influence of the unsteady jet.

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The flow force of a spool valve can be decreased by circulating the flow in a compensation bucket. The effects of its geometric parameters on the compensation were investigated experimentally by the authors and reported on. The detail of velocity profile and pressure distribution of flows in compensation buckets were not yet studied in the report. However, for the rational design of a flow-force compensated spool valve, the practical use of numerical experiment for flows in valves is strongly desired. Thus, in this research, a boundary element method utilizing velocity components V_x, V_y, vorticity ω and pressure p as primary variables is investigated to develop a numerical simulation program for flows in the spool valves. We found that the above V_x-V_y-ω-p method would give zigzag pressure solution and could not obtain true pressure values. Then, we resolved this troublesome hurdle by introducing a simple smoothing method. Although the usefulness and validity of this computation method are verified in various cases, for simplicity we only show one typical example for laminar flow between parallel walls at Reynolds Number 500.

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In order to design a flow-force compensated spool valve rationally, the practical use of numerical experiment for flows in hydraulic valves is strongly desired. On the other hand, the boundary element method have been remarkably advanced in recent years. In this research, we refined a V_x-V_y-ω-p method to devise a numerical analysis for the spool valve.
Firstly, we treated flows in spool valves two dimensionally and paid particular attention to the flow in the downstream compensation bucket of valves. From the solution of V_x, V_y, ω and p up to Reynolds number280, the tendency of flow-force compensation by a two-dimensional bucket was clarified. The purpose of this study is to establish a simple numerical method suitable for the analysis of flows in valves and obtain the optimum bucket shape for flow-force compensation.

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