• Transactions of The Korea Fluid Power Systems Society
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• v.6 no.2
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• pp.22-30
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• 2009

An in-process method of diagnosing the spool wear of hydraulic servovalves was explored. The diagnostic method discussed in this paper is for force-control hydraulic servo systems. The key principle used is that pressure sensitivity of a servovalve drops as the valve spool wears out so that it is possible to determine the spool condition by monitoring pressure sensitivity. A diagnostic algorithm was developed and evaluated through numerical simulation and experiments. Two major steps of diagnosis are the evaluation of null bias of the servovalve and the approximation of pressure sensitivity, both of which could be successfully done during normal operation of a servo system. The difference between a new servovalve and a worn valve could be clearly detected in-process, and the diagnostic test was found to be repeatable.

• Tribology and Lubricants
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• v.25 no.1
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• pp.13-19
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• 2009

The spools in most hydraulic spool type control valve have several circumferential grooves to pre-vent well known hydraulic locking problems which result in high friction force and excessive wear. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the flow and lubrication characteristics of grooved hydraulic spool valve. The stream lines and pressure distributions are obtained for various groove cross sectional shapes and film thicknesses. The stream lines are highly affected by groove cross sectional shape but pressure distributions mainly depend on the film shape and its magnitude. Therefore the numerical method adopted in this paper and results can be use in designing of various grooved spool valve.

• Journal of Applied Reliability
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• v.14 no.4
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• pp.230-235
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• 2014

The failure modes of pneumatic directional control valves include leakage, wear of the spool seal, and sticking of the spool. Among them, the main failure mode of the valve is leakage. The leakage is caused by the wear of the spool seal. However, due to the characteristics of the seal material, the leakage rate is fluctuated a lot rather than constantly increased over time. If life analysis is performed using the first time data of leakage failure, predicted life cycles can be different from the real life cycles. This paper predicts life cycles of the pilot pneumatic directional control valve based on the three point moving average which considers the average of the fluctuating leakage rate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1183-1188
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• 2013

The reliability of hydraulic equipment used in power plants is especially important because failures that occur in the power plant can have a great ripple effect on human lives and financial losses. In this study, specimens using the materials used in the spool and sleeve of hydraulic valves of power plants have been produced, heat-treated, and tested under the precipitation conditions of phosphate ester hydraulic fluid with a variety of conditions. 23 full factorial designs have been applied to evaluate the significance of factors that affect the wear loss of the specimen, specifically, the load, velocity, and temperature. The significance evaluation was performed on the main effects and two-way interactions for wear loss based on the experiment results, and the mathematical equations between the wear loss and the three factors were derived from the analysis results.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.218-223
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• 1997

유압장치의 핵심부품인 유압 제어밸브(hydraulic control valve)는 유압펌프 등에 의하여 가압된 유압유의 압력과 유량을 제어하고 유동방향을 변화시키는 주요기능을 수행한다. 특히, 대부분의 제어밸브는 스푸울(spool)과 슬리브(sleeve)를 기본구조로 채용하고 있다. 피스톤 형상인 스푸울이 슬리브내를 왕복운동하면 스푸울과 슬리브 사이의 간극(clearance)에서는 점성유체인 유압유의 윤활작용에 의하여 원주방향으로 비대칭인 유체압력이 발생한다. 이 결과로 스푸울에 측력(lateral force)이 작용하며, 조건에 따라서는 스푸울에 작용하며, 조건에 따라서는 스푸울에 작용하는 마찰력이 증대할 뿐만 아니라 스푸울과 슬리브의 내벽에 과도한 마멸(wear)을 유방시키기도 하여 제어밸브의 성능을 크게 저하시키기도 한다. 유압공학분야서는 이를 유체고착(hydraulic locking) 현상이라고 부른다. 본 논문에서는 항공기 Flap actuator의 Selector manifold에서 사용되는 스푸울 밸브의 성능에 큰 영향을 미칠 것으로 예상되는 스프울과 슬리브 사이 간극에서의 윤활특성을 이론적으로 조사하고자 한다.

• Transactions of The Korea Fluid Power Systems Society
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• v.3 no.1
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• pp.7-14
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• 2006

In this paper, an in-process diagnosis method for performance of position control servo system was studied, which was based upon null bias, slew-rate ratio and delay time measurement. Slew-rate ratio and delay time were analyzed by theoretical analysis, computer simulation and experiment. As a result of these analysis, when spool of servovalve was weared, slew-rate ratio was decreased and delay time was increased.