• 한국기계가공학회지
• /
• 제17권1호
• /
• pp.69-75
• /
• 2018

This study aims to provide ways to achieve structural improvements of the internal flow path of the discharge plenum of a swash plate piston pump valve block vulnerable to cracks. This paper corresponds to Part I, which consists of a structural analysis of the valve block, identification of the stress distribution and stress raisers, and creation of a Simple Model of the valve block to review the optimal design. Structural analysis was performed by assigning the same conditions as those found in the valve block model, and the design was reviewed by examining three different design improvement plans for the internal flow path of the discharge plenum.

• 대한기계학회논문집
• /
• 제1권2호
• /
• pp.65-72
• /
• 1977

Major problems in the design and use of refief valve are (a) chattering because of instability, (b) excessive pressure differential which makes the valves crack far below maximum pressure diminishing useful flow in the system. In this study, A magnet-coupled relief valve is investigated theoretically and experimentally in order to improve the performance of a conventional direct type reliefvalve. A theory is developed to predict the performance, response, and stability of the magnet-coupled valve taking into account the delivery line response. In the experiment, a typical magnet-coupled relief valve is designed on the basis of the analytical results; the discharge rates are measured varying the supply pressure, and both the pressure-time curves and valve displacament-time curves are recorded providing the supply pressures greater than the setting pressure. The measured override characteristic curves are then compared with those of conventional pilot type and direct type releif valves. It is showm that the excessive pressure differential of a magnet-coupled relief valve becomes less than that of a conventional direct type valve. It is also shown that the most important chatacteristic of a magnet-coupled relief valve is to eliminate valve chattering due to instability regardless of the magnitude of setting pressures and discharge rates, which suggests wide applications of the idea of the use of a magnet in the design of hydraulic valves.

• Journal of Mechanical Science and Technology
• /
• 제18권6호
• /
• pp.1019-1025
• /
• 2004

Pressure variation is one of the major sources on noise emission in the axial type oil piston pumps. Therefore, it is necessary that the pressure variation characteristics of the oil hydraulic piston pumps be clarified to reduce the pump noise. Pressure variations in a cylinder at the discharge region and the pump noise were simultaneously measured with discharge pressures and rotational speeds during the pump working. To investigate the effects of the pre-compression and the V-notch in the valve plate, we used the three types of valve plates. In this research, it is clear that the pressure variation characteristics of axial type oil piston pumps is deeply related to the pre-compression and to the V-notch design in valve plate. Therefore, we could reduce the pump noise by using the appropriate pre-compression angle and the notch design that are between the suction port and the discharge port in valve plate.

• 한국자동차공학회논문집
• /
• 제12권2호
• /
• pp.101-108
• /
• 2004

Recently, a semi-active shock absorber has been taking interest because of its low cost and simple structure than the active one. CFD analysis has been conducted to investigate the continuous and variable damping characteristics of the semi-active shock absorber. Also, the flow resistance characteristics of a spool valve has been examined to identify individual parameters(namely, exponent and discharge coefficient) of pressure-flow rate relation needed for the accurate valve modeling. The flow field in the damping valve was simulated using the commercial code, CFX-5.3. The numerical results showed reasonable agreement with the experimental outputs. The pressure distribution with the variation of spool opening length and volume flow rate were discussed in detail. And the continuous and variable damping performance was found clearly. The individual parameters of spool valve were obtained as a function of orifice area. The exponent and discharge coefficient were fitted in with the first and the third polynomial respectively.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
• /
• pp.259-264
• /
• 2000

The functions of the plug valve are the control of flow rate as well closing and opening pipe lines. Analyses on the flow characteristics in plug valve port are required to improve the performance and safety at severe operating conditions such as high-pressure and high-temperature. In this study, numerical analyses are carried out with varying the opening rate (fraction of the full open to close) of the valve and the shapes of valve Uk: straight, convex, concave and mixed shapes. The parameters influencing the flow characteristics in the valve are the discharge coefficient( $C_v$) and the resistance coefficient( K). Therefore, the distributions of static pressure, velocity vector and stream lines are investigated, and $C_v$ and K are calculated in each opening rate and shape. In case of full open, the static pressure passed through the valve port has almost been recovered. However, in case of other opening rates, the pressure does not permanently regained due to pressure drop leading to loss. This phenomenon in each shape of the valve shows the different behaviors. Calculation results show that the mixed shape has the best flow attribute.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2003년도 학술대회지
• /
• pp.329-334
• /
• 2003

Design of pre-compression region(trapping region) of the valve plate is an important element to minimize the pressure fluctuation in a cylinder and in discharge process, and pump noise. In this study, we tried to prove what the characteristics of the oil hydraulic pump would be according to the angle of the trapping region. Three kinds of asymmetrical valve plates were used. As a result, we found that by designing the trapping region, the slope of the pressure rise in the cylinder port from low-pressure suction region to high-pressure discharge region is relaxed and the pressure fluctuation width and the discharge pressure pulsation are reduced. Therefore, because the pump gets smooth pressure fluctuation and low fluid Impact, the pump noise is reduce.

• Journal of Chest Surgery
• /
• 제7권2호
• /
• pp.189-200
• /
• 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.

• 한국안전학회지
• /
• 제21권5호
• /
• pp.12-16
• /
• 2006

This paper deals with the noise evaluation and noise reduction of a reciprocating air-compressor. The reciprocating air-compressor is widely used in the small and medium sized industrial firms, many employees exposed and irritated by their noise in the workplace. Thus, appropriate noise control actions should be taken to prevent hearing loss due to the its noise exposure. Lead-wrapping techniques are employed to identify the contribution of principal noise sources which are generally known to be motor, belts, suction valves, discharge valves, moving parts, and flow-induced noise caused by edges or discontinuities along the flow path including expansions, contractions, junctions and bends. As a result, the main noise sources of the air-compressor are categorized by the suction and discharge noise, valve noise, and compressed air tank noise. Based on the investigations, mufflers are designed to reduce both the suction and discharge noise and the compressed-air tank noise. Instead of the conventional valve plate, polyethylene resin is used the reduction of valve impact noise. In addition, attempts are made to reduce the valve noise propagation to the cylinder head and the compressor tank by using the insulation casings. As a result of the countermeasure plans, a noise reduction up to 10dB(A) could be achieved for the air-compressor.

• 연구논문집
• /
• 통권33호
• /
• pp.39-51
• /
• 2003

This paper deals with the noise measurement and evaluation method of a reciprocating air-compressor and its noise reduction. Lead-wrapping techniques are employed to identify the contribution of principal noise sources which are generally known as motor, belts, suction/discharge valves, moving piston, and flow-induced noise which are caused by edges or discontinuities along the flow path e.g. expansions, contractions, junctions and bends. As a result, it can be found that main noise sources of the air-compressor can be categorized by the suction/discharge noise, valve noise, and compressed-air tank noise. Based on the investigations, mufflers are designed to reduce both the suction/discharge noise and the compressed-air tank noise. Instead of the conventional valve plate, engineering plastics are used as a new one for the reduction of valve impact noise. In addition, attempts are made to reduce the valve noise propagation to the cylinder head and the compressor tank by using the insulation casings in the cylinder head. As a result of the countermeasure plans, it can be achieved that the noise reduction of the air-compress is up to 10 dB.

• 한국관개배수논문집
• /
• 제5권2호
• /
• pp.33-40
• /
• 1998

In this research the valve-opening calculation program for operation of valve was developed to determine the valve-openings corresponding to discharges in pipeline system. Personal Computers can be used for hydraulic calculations of the steady flow condit