• Title/Summary/Keyword: Stem Friction

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A Study on the Stem Coefficient of Friction of Motor- operated Gate/Globe halves

  • Jeoung, Rae-Hyuck;Park, Sung-Keun;Lee, Do-Hwan;Kim, Yang-Seok
    • Nuclear Engineering and Technology
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    • v.35 no.2
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    • pp.133-143
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    • 2003
  • Stem-stem nut coefficient of friction(COF) in motor-operated gate/globe valves is one of the important factors which determine the performance of the valve/actuators. The COF is affected greatly by the type and condition of the stem-stem nut lubricants, environmental parameters, surface condition of the stem/stem-nuts, and the number of strokes after the lubrication. In this paper, the measured data of the COFs at stem threads of some safety-related motor-operated gate/globe valves in domestic nuclear power plants are presented. In addition, the performance of the lubricants is evaluated by comparing the COFs among those valves. The results show that the measured COF at torque switch trip are higher than the unwedging COF and conservatively applicable to the unwedging COF. It is also shown that the lubricating performance based on the measured COFs varies with the lubricants.

A Study on the Bounding Value of Valve Performance Parameters for Motor Operated Flexible Wedge Gate Valve (모터구동 Flexible Wedge형 게이트밸브의 밸브 성능인자 Bounding Value에 대한 연구)

  • Kim, Dae-Woong;Yoo, Seong-Yeon;Park, Sung-Keun;Lee, Do-Hwan
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.5
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    • pp.46-53
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    • 2007
  • Stem friction coefficient and valve factor are very important parameters for the evaluation of valve performance. In this study, the characteristics of stem friction coefficient and valve factor are analyzed, and thor bounding value is determined. The hydraulic testing is performed for many flexible wedge gate valves in the plant and statistical method is applied to the determination of bounding value. According to the results of this study, stem friction coefficient does not change much with differential pressure, and the bounding value of closing stroke is higher than that of opening stroke. The valve factor of valves with high differential pressure is higher than that of valves with medium differential pressure. It means valve factor is more sensitive to the differential pressure than the stem friction coefficient. Valve factor of the closing stroke is higher than that of opening stroke due to piston effect.

Effect of Stem Design on Contact Pressure and Stress Distribution of End-of-stem in Revision TKR (슬관절 재전치환술용 경골 삽입물 형상이 주대 말단부의 접촉압력과 응력 분포에 미치는 영향)

  • Kim, Yoon-Hyuk;Kwon, Oh-Soo;Park, Si-Mon
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.11 s.188
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    • pp.126-134
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    • 2006
  • In this study, the effect of stem-end design on contact pressure and stress distribution in revision TKR was investigated using finite element method. The finite element model of tibia, including the cortical bone, the cancellous bone and canal, was developed based on CT images. The implant models with various stem lengths, diameters, friction coefficients, and press-fit effects were considered. The results showed that the longer stem length, the stronger press-fit, the bigger stem diameter, and the higher friction coefficient increased both peak contact pressure and Von-Mises stress distributions. The results supported the clinical hypothesis that peak contact pressure and stress are related to the stem end pain. The results of this study will be useful to design the stem and reduce the end-of-stem pain in revision TKR.

Transient analysis of lubrication with a squeeze film effect due to the loading rate at the interface of a motor operated valve assembly in nuclear power plants

  • Jaehyung Kim;Sang Hyuk Lee;Sang Kyo Kim
    • Nuclear Engineering and Technology
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    • v.55 no.8
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    • pp.2905-2918
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    • 2023
  • The valve assembly used in nuclear power plants is important safety-related equipment. In the new standard, the physical attributes are measured using a valve diagnosis test, which is used in the expansion to other non-tested valves using a quantitative test-basis methodology. With a motor-operated actuator, the state of stem's lubrication is related to physical attributes such as the stem factor and the friction coefficient. This study analyzed the numerical transient of fluid and solid lubrication with a squeeze film effect due to the loading rate on the stem and the stem nut using the experimental data. The differential equation that governs the motion mechanism of the stem and stem nut is established and analyzed. The flow rate, the fluid and the solid contact forces are calculated with the friction coefficient. Finally, we found that a change in the friction coefficient results from a change of the shear force in the solid contact mode during the interchange process between the solid contact mode and the fluid contact mode. The qualitative understanding of the squeeze film effect is expanded quantitatively for forces, thread surface distance, velocity, and acceleration, with consideration of the metal solid contact and fluid contact.

A comparison analysis of the stem lubricant performance for motor operated valve used in nuclear power plants (원자력발전소에서 사용중인 모터구동밸브 스템 윤활유의 성능 비교 분석)

  • Kim, Dae-Woong;Kim, Yang-Seok;Park, Chi Young;Lee, Sang Guk
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.11 no.2
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    • pp.6-12
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    • 2015
  • In this study, the performance test was carried out under various operation conditions targeting four representing types of lubricant which are mostly used in nuclear power plants, and mutually compared the characteristic and performance of lubricant. Especially, introducing the concept of the thread friction coefficient (hereinafter, TFC), which makes the friction relation between the stem nut and stem screw dimensionless. The test was performed to compare the lubricant performance for the four kinds of lubricant (Texaco, Alvania, Mobilux, MOVLL). In a test of the room temperature stem, the TFC of MOV Long Life shows the lowest value, next to Alvania EP2, Texaco EP2, and Mobilux EP0 in that order. And in a test of the high temperature stem, the TFC of Texaco EP2 shows the lowest, next to MOV Long Life, Alvania EP2, and Mobilux EP0 in that order. From the test result of the aging condition, three types of lubricant (MOV LL, Texaco EP2, Alvania EP2) show similar patterns up to 36 months, but in 60 months, the TFC of lubricant are increased rapidly.

Measurement of Mechanical and Physical Properties of Pepper for Particle Behavior Analysis

  • Nam, Ju-Seok;Byun, Jun-Hee;Kim, Tae-Hyeong;Kim, Myoung-Ho;Kim, Dae-Cheol
    • Journal of Biosystems Engineering
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    • v.43 no.3
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    • pp.173-184
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    • 2018
  • Purpose: This study was conducted to investigate the mechanical and physical properties of a Korean red pepper variety for particle behavior analysis. Methods: Poisson's ratio, modulus of elasticity, shear modulus, density, coefficient of restitution, and coefficient of friction were derived for "AR Legend," which is a domestic pepper variety. The modulus of elasticity and Poisson's ratio were measured through a compression test using a texture analyzer. The shear modulus was calculated from the modulus of elasticity and Poisson's ratio. The density was measured using a water pycnometer method. The coefficient of restitution was measured using a collision test, and the static and dynamic friction coefficients were measured using a inclined plane test. Each test was repeated 3-5 times except for density measurement, and the results were analyzed using mean values. Results: Poisson's ratios for the pepper fruit and pepper stem were 0.295 and 0.291, respectively. Elastic moduli of the pepper fruit and pepper stem were $1.152{\times}10^7Pa$ and $3.295{\times}10^7Pa$, respectively, and the shear moduli of the pepper fruit and pepper stem were $4.624{\times}10^6Pa$ and $1.276{\times}10^7Pa$, respectively. The density of the pepper fruit and the pepper stem were $601.8kg/m^3$ and $980.4kg/m^3$, respectively. The restitution coefficients between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.383, 0.218, 0.277, 0.399, and 0.148, respectively. The coefficients of static friction between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.455, 0.332, 0.306, 0.364, and 0.404, respectively. The coefficients of dynamic friction between a pepper fruit and plastic and a pepper stem and plastic were 0.043 and 0.034, respectively.

A Study for the Improvement Method of Flexible Wedge Gate Valve Operation Capability (Flexible Wedge Gate 밸브의 운전 성능향상 방안에 관한 연구)

  • Kim, Dae-Woong;Lee, Do-Hwan;Kang, Sin-Chul;Kim, In-Whan;Park, Sung-Keun
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.644-651
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    • 2001
  • The purpose of this study is to develop the improvement method of MOV(Motor Operated Valve) operability without major modification or change of MOV which needs a great expense and manpower. We studied valve stem lubrication, stem packing thrust and actuator control switch which could give an major effect to MOV operability, and found the some consequences. First, the stem/stem-nut friction coefficient and stem factor is significantly effected by stem lubrication state. Second, the measured packing thrust value is appeared higer than the design value for tested valves and the preparation of optimal value selection criteria is needed. Finally, optimization of MOV control switch is another major factor for MOV operability and structual integrity.

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A Study on the Packing Friction Estimation of Power-Operated Valves in Nuclear Power Plants (원전 동력구동 밸브 패킹 마찰력 예측에 관한 연구)

  • Ryu, Dong Hwa;Lee, Young Shin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.11
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    • pp.1053-1060
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    • 2013
  • The purpose of this study is to estimate the packing friction of power-operated valve in nuclear power plants. The roll of packing in valve is preventing leakage through stem. Packing friction is highly depend on gland nut tightness which means higher reliability in sealing is lower operability. For the estimation of friction, we used statistical analysis and experimental analysis. In experimental approach, we have performed packing fY test and applied it to valve field test. In statistical approach, we have used 10 years DB of safety-related valve in nuclear power plant and analyzed packing friction based on confidence interval of sample. The comparison of two results shows that statistical analysis for packing friction are more accurate than fY analysis even though both approach have error compared to measured value but we confirmed that statistical approach is proper way to estimate packing friction.

A Method of ROL Improvement for the Motor Operated Gate Valve Operating in the High Differential Pressure Condition (고차압에서 운전되는 모터구동게이트밸브의 부하율 향상 방안)

  • Kim, D.W.;Park, S.G.;Hong, S.Y.;Yooh, S.Y.
    • 유체기계공업학회:학술대회논문집
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    • 2003.12a
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    • pp.562-567
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    • 2003
  • This paper presents the method of Rate of Loading(ROL) improvement for the Motor Operated Gate Valve operating in high differential pressure condition. The character of ROL and Stem Factor is analyzed. Static test and dynamic test were performed and acquired the diagnosis signal for the valve closing stroke. The result of this study is the modification of stem factor is very important factor for the ROL improvement. In order to obtain the same value of dynamic test thread friction coefficient stem and stem nut should be combined appropriately.

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