• 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.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.40-46
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• 2017

Small valves including ball valves, gate valves and butterfly valves have been adopted in the fields of steam power generation, petrochemical industry, carriers, and oil tankers. Butterfly valves have normally been applied to fields where in narrow places installing the existing valves such as gate valves and ball valves have proven difficult due to the surrounding area and the heavier of these valves. Butterfly valves are used to control the mass flow of the piping system under low pressure by rotating the circular disk installed inside. The butterfly valve is benefitted by having simpler structure in which the flow is controlled by rotating the disc circular plate along the center axis, whereas the weight of the valve is light compared to the gate valve and ball valve above-mentioned, as there is no additional bracket supporting the valve body. The manufacturing company needs to acquire the performance and life test equipment, in the case of adopting the improving factors to detect leakage and damage on the seat of the valve disc. However, small companies, which are manufacturing the industrial valves, normally sell their products without the life test, which is the reliability test and environment test, because of financial and manpower problems. Furthermore, the failure mode analysis of the products failed in the field is likewise problematic as there is no system collecting the failure data on sites for analyzing the failures of valves. The analyzing and researching process is not arranged systematically because of the financial problem. Therefore this study firstly tried to obtain information about the failure data from the sites, analyzed the failure mode based on the field data collected from the customers, and then obtained field data using measuring equipment. Secondly, we designed and manufactured the performance and life test equipment which also have the real time monitoring system with the naked eye for the butterfly valves. The concept of this equipment can also be adopted by other valves, such as the ball valve, gate valve, and various others. It can be applied to variously sized valves, ranging from 25 mm to large sized valves exceeding 3000 mm. Finally, this study carries out the life test with square wave pressure, using performance and life test equipment. The performance found out that the failures from the real time monitoring system were good. The results of this study can be expanded to the other valves like ball valves, gate valves, and control valves to find out the failure mode using the real time monitoring system for durability and performance tests.

• Journal of Chest Surgery
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• v.7 no.2
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• pp.189-200
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• 1974

The mitral valve replacement with Beall prosthetic valve was performed on three patients, and double valve replacement. aortic and mitral valve, was performed in this department.1) The preoperative studies about the first case were compatible with mitral steno-insufficency.The diseased mitral valve was replaced with the medium sized Beall prosthetic valve under the cardiopulmonary hypass using hypothermic hemodilution technique. The total perfusion time was eighty minutes. Immediate postoperative course was smooth, but this patient was died of asphyxia due to tracheomalacia complicated after tracheostomy 3 months after operation. Autopsy on this patient revealed that no thrombus and no ball variance could be found, and endothelization on the valve cuff was satisfactory. 2) The preoperative studies on the second case were compatible with mitral insufficiency. The diseased mitral valve was replaced with the medium sized Beall prosthetic valve under the cardiopulmonary bypass using hypothermic hemodilution technigue. The total perfusion time was 123 minutes. This patient was discharged in good condition and follow-up study after 16 months revealed the patient had enjoyed healthy life. 3) The preoperative studies about the third case were compatible with aortic insufficiency and mitral stenoinsufficiency. The diseased valves were replaced with type 2 sutureless Magovern aortic valve and the medium sized Beall mitral prosthesis under cardiopulmonary bypass using hypothermic hemodilution technIque and coronary artery perfusion. The total perfusion time was 155 minutes. This patient was discharged in good condition, but thromboembolism was developed 2 months after discharge. 4) The preoperative studies about the fourth case were compatible with mitral insufficiency. The diseased mitral valve was replaced with the medium sized Beall prosthetic valve. The total perfusion time was 132 minutes. The atrioventricular block developed just after operation but converted to normal sinus rhythmn on the third postperative day. The preoperative NYHA functional classification IV was converted to Class 1 or 11 at the time of discharge and this patient enjoyed healthy life. Attendum; The fifth case, nineteen years old male with mital insufficiency underwent Beall valve replacement and his course was uneventful 2 weeks after operation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.820-825
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• 1996

This paper is concerned with effective operating method of pneumatic on-off valves for improving position control accuracy, valve life-time and position settling time using modified pulse width modulation with dead-zone. The pneumatic system using on-off valves studied in this paper has advantage of simple construction and low cost compared with a system with servo-valves. The performance of proposed control system is investigated experimentally for the position control of a pneumatic cylinder using on-off valves. Experimental results show that the proposed algorithm for valve operation can be used to obtain fast and accurate position control and to prevent on-off valves from unnecessary switching.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1445-1451
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• 2011

Pneumatic valves are widely used parts that have the ability to control the air supplied to automation systems. However, if failure occurs in a pneumatic valve, it may affect the entire system and could lead to huge losses, depending on the characteristics of the system at the time of failure. Because of this significant risk and the level of consumer demand for reliability, there has been much study on ensuring the reliability of products by predicting valve lifetime distributions and degradation characteristics. In this paper, in order to determine the main factors useful for predicting the lifetime of a pneumatic valve, the scale parameter and $B_{10}$ life time value of the widely used plug-in-type pneumatic manifold valves were measured using complete observational data on the valve lifetimes. And also the property of life distribution has been distribution-suitabilityreviewed by correlation coefficients, the degradation characteristics of valve has been presented by the result of analysis through dynamic response time test and leakage test.

• Journal of Aerospace System Engineering
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• v.4 no.2
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• pp.16-20
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• 2010

In General, the hydraulic system of T-50 Advanced Trainer is applied to flight control system, wheel & Brake system and fuel system for aircraft operation. The hydraulic system is operation with pressure of 3000psi. and many mechanical parts which is operated by hydraulic system has been stressed in incomplete environment same as heat and friction. for example, Oil leakage had occurred in the shutoff valve of FFP used in a certain period of time. After study, The crack progressed by fatigue due to the irregular hydraulic pressure and vibration has been identified as the reason of oil leakage. This paper presents life cycle extension plans of FFP shutoff valve by configuration improvements of shutoff valve and FFP hydraulic motor.

• Journal of Chest Surgery
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• v.22 no.6
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• pp.1036-1043
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• 1989

Seventy eight patients underwent operation for combined multiple valve disease, with an overall early mortality of 14.1 % from January, 1983 to September, 1988 in the department of thoracic and cardiovascular surgery of Pusan National University Hospital. All of the above cases had combined multiple valve procedures. There were 33 mitral valve replacements and tricuspid annuloplasties, 33 aortic and mitral valve replacements, 5 aortic and mitral valve replacements with tricuspid annuloplasties, 3 aortic valve replacements and mitral annuloplasties, 1 open mitral commissurotomy and tricuspid annuloplasty and, 1 mitral valve replacement and primary closure of tricuspid valve cleft, 1 mitral valve replacement and aortic commissurotomy, 1 mitral, aortic and tricuspid valve replacement were done. 44 were male and 34 were female and the age distribution was from 14 to 57 with mean 38 year old. According to NYHA[New York Heart Association] classification, 49 patients were class I, 19 patients were class Il and 10 were class IV. Average perfusion time was 205.3 minutes. The live patients perfusion time was 178.7 minutes while that of dead ones was 272.0 minutes. Early deaths within 30 days from operation were 11 cases, 6 of which were due to low cardiac output, 3 were acute renal failure and 2 were cardiac rupture. The 65 patients were followed up from 2 to 30 months for a total 20.6 patient years. 1 patient committed suicide because of postoperative depression 1 year after operation. All of the survivors were enjoying their daily life and their NYHA class was superior to the preoperative ones.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.456-459
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• 2011

The Dual-type Solenoid Valve was developed for a domestic production of a fuel-supply valve on the satellite attitude control thruster system. The satellite valve using a hydrazine as a fuel must fulfill the cycle life, shock, vibration and the environment of an extremely low temperature In addition to the basic performance of the response time, mass flow and leakage etc.. in this paper, the design, production and performance experiment using the nitrogen pneumatic equipment were conducted.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.500-507
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• 1989

The improvement of volumetric efficiency of air charging into combustion chamber is a primary requirement to obtain better mean effective pressure of an engine. Since parameters such as the air resistances in intake and exhaust flow passages, valve lift and valve timing influence greatly to the volumetric efficiency, it is very convenient and time saving if we can optimize these parameters by computation before we enter into long time fact finding engine tests. In this study we have developed a semi-empirical engine simulation program for the determinations of intake and exhaust valve timings, valve lifts, intake and exhaust port diameters in order to obtain highest volumetric efficiency. In this computation it requires only the measured variational pressures in intake and exhaust port. Using these variational pressures as an input data for our simulation program, we can calculate volumetric efficiency more accurately and can save computing time drastically. To confirm the validity of our simulation program we have made engine operation test in parallel and taken the experimental data. Comparing the computation result with the experimental data obtained through real engine test it has shown only the difference of 3%.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.5
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• pp.77-83
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• 2020

The operating characteristics of a main oxidizer shut-off valve have been examined by life-cycle tests in which the valve operates as many times as is required at room and cryogenic temperatures. It is shown that there is no significant change of the operating characteristics in the course of the life-cycle tests. The critical pressures and principal forces, which represent the operating characteristics, differ at each operating time by less than about 3%. These qualified operating characteristics of the valve are expected to play an indispensible role in the stable startup and shutdown of a liquid rocket engine.