• Journal of Mechanical Science and Technology
• /
• v.15 no.7
• /
• pp.1061-1071
• /
• 2001

The present study investigated design parameters of shunt valves and anti-siphon device used to treat patients with hydrocephalus. The shunt valve controls drainage of cerebrospinal fluid (CSF) through passive deflection of a thin and small diaphragm. The anti-siphon device(ASD) is optionally connected to the valve to prevent overdrainage when the patients are in the standing position. The major design parameters influencing pressure-flow characteristics of the shunt valve were analyzed using ANSYS structural program. Experiments were performed on the commercially available valves and showed good agreements with the computer simulation. The results of the study indicated that predeflection of the shunt valve diaphragm is an important design parameter to determine the opening pressure of the valve. The predeflection was found to depend on the diaphragm tip height and could be adjusted by the diaphragm thickness and its elastic modulus. The major design parameters of the ASD were found to be the clearance (gap height) between the thin diaphragm and the flow orifice. Besides the gap height, the opening pressure of the ASD could be adjusted by the diaphragm thickness, its elastic modulus, area ratio of the diaphragm to the flow orifice. Based on the numerical simulation which considered the increased subcutaneous pressure introduced by the tissue capsule pressure on the implanted shunt valve system, optimum design parameters were proposed for the ASD.

• Journal of Korean Neurosurgical Society
• /
• v.46 no.4
• /
• pp.370-377
• /
• 2009

Objective : There is no definite adjustment protocol for patients shunted with programmable valves. Therefore, we attempted to find an appropriate method to adjust the valve, initial valve-opening pressure, adjustment scale, adjustment time interval, and final valve-opening pressure of a programmable valve. Methods : Seventy patients with hydrocephalus of various etiologies were shunted with programmable shunting devices (Micro Valve with $RICKHAM^{(R)}$ Reservoir). The most common initial diseases were subarachnoid hemorrhage (SAH) and head trauma. Sixty-six patients had a communicating type of hydrocephalus, and 4 had an obstructive type of hydrocephalus. Fifty-one patients had normal pressure-type hydrocephalus and 19 patients had high pressure-type hydrocephalus. We set the initial valve pressure to $10-30\;mmH_2O$, which is lower than the preoperative lumbar tapping pressure or the intraoperative ventricular tapping pressure, conducted brain computerized tomographic (CT) scans every 2 to 3 weeks, correlated results with clinical symptoms, and reset valve-opening pressures. Results : Initial valve-opening pressures varied from 30 to $180\;mmH_2O$ (mean, $102{\pm}27.5\;mmH_2O$). In high pressure-type hydrocephalus patients, we have set the initial valve-opening pressure from 100 to $180\;mmH_2O$. We decreased the valve-opening pressure $20-30\;mmH_2O$ at every 2- or 3-week interval, until hydrocephalus-related symptoms improved and the size of the ventricle was normalized. There were 154 adjustments in 81 operations (mean, 1.9 times). In 19 high pressure-type patients, final valve-opening pressures were $30-160\;mmH_2O$, and 16 (84%) patients' symptoms had nearly improved completely. However, in 51 normal pressure-type patients, only 31 (61%) had improved. Surprisingly, in 22 of the 31 normal pressure-type improved patients, final valve-opening pressures were $30\;mmH_2O$ (16 patients) and $40\;mmH_2O$ (6 patients). Furthermore, when final valve-opening pressures were adjusted to $30\;mmH_2O$, 14 patients symptom was improved just at the point. There were 18 (22%) major complications : 7 subdural hygroma, 6 shunt obstructions, and 5 shunt infections. Conclusion : In normal pressure-type hydrocephalus, most patients improved when the final valve-opening pressure was $30\;mmH_2O$. We suggest that all normal pressure-type hydrocephalus patients be shunted with programmable valves, and their initial valve-opening pressures set to $10-30\;mmH_2O$ below their preoperative cerebrospinal fluid (CSF) pressures. If final valve-opening pressures are lowered in 20 or $30\;mmH_2O$ scale at 2- or 3-week intervals, reaching a final pressure of $30\;mmH_2O$, we believe that there is a low risk of overdrainage syndromes.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.5
• /
• pp.719-726
• /
• 1997

The proportional pressure control valve having versatile functions and higher performance is an essential conponent in the open loop controlled rear wheel steering gear of the four wheel steering system in a passenger car. In this study, the authors suggest a new type of load pressure feedback mechanism which can make it easy to change the range of controlled pressure without changing the capacity of solenoid. The concept of suggested mechanism, composed of the pressure chamber with throttles in series, was described. The mathematical model was derived from the rear wheel steering gear consisting of a valve and a cylinder for the purpose of analyzing the valve characteristics. And the programme for computing the characteristic of the valve was developed. Experiments were performed to confirm the performance of the valve and computations were carried out to ascertain the usefulness of the developed programme. The results from computations fairly coincide with those from experiments. And the results from experiments and computations show that the performance of new valve was as good as that of the already developed one and the new valve has advantages such as the easiness of changing the range of controlled pressure and the decrease of power loss at neutral position without the decline of performance.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.288-293
• /
• 2001

This paper presents the water-hammer effect due to the rapid opening and closing of isolation valve and thruster valve in the spacecraft propulsion system. The single propellant feed system was modeled to investigate the maximum peak pressure due to the water-hammer effect. The test parameters are tank supply pressure, shape and throat length of orifice and line length. Kerosene was used as the inert simulant propellant liquid instead of hydrazine. As downstream line length after isolation valve increased from 1.5 to 2.5m, the maximum line-filling water-hammer peak pressure decreased, but the average time interval between peak pressures increased. The maximum line-filling water-hammer peak pressure with orifice was lower than without orifice, and the maximum line-filling water-hammer peak pressure with orifice at the back of isolation valve was lower than with orifice in front of isolation valve. Without orifice, the maximum water-hammer peak pressure due to the rapid opening and closing of the thruster valve was about 126% of tank supply pressure. With orifice, it decreased. As orifice throat length increased, it decreased. The maximum water-hammer peak pressure due to the rapid closing of the thruster valve with converging-diverging orifice was lower than normal orifice. It was found that the orifice as a means of pressure drop was very effective to reduce the water hammer peak pressure at the thruster valve. The results of this study can be used for the design of spacecraft liquid propulsion feed system.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1994.10a
• /
• pp.472-477
• /
• 1994

The lockup clutch is embeded on torque converter of automatic transmission to prevent the efficiency deterioration of torque converter in high speed. For improving fuel consumption rate, it is desirable to engage the lockup clutch earlier. But, it results in degrading shift quality, due to the transient torque. The transient clutch pressure which affects the shifting quality, should be controlled properly. In this study, to solve the problem, it is analysed the hydraulic circuit of lockup system including line pressure regulating circuit, established the nonlinear model, and designed the PID controller. The line pressure is supplied to the lockup clutch through the lockup control valve by switching the lockup solenoid valve on. In order to control the transient pressure actively, it is needed to control the lockup solenoid valve by closed loop control. The lockup solenoid valve is 2-way on-off valve, and is adequate for PWM control. To reduce the pressure chattering, the carrier frequency is increased. Target pressure profile is computed from optimized velocity difference profile throuth dynamic equation of vehicle system.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.1
• /
• pp.75-80
• /
• 2002

Cycle life tests have been carried out to evaluate the influence of safety valve pressure on valve regulated lead/acid batteries under deep cycling applications. Batteries were cycled at 5 hour rates at 100% DOD, and safety valve pressure was set to 1.08 and 2.00 bar, respectively. The batteries lost 248.3 g and 235.3 g of water for each case after about 1,200 cycles, but the cyclic performances of the batteries were comparable. Most of the gas of the battery during discharging was hydrogen, and the oxygen concentration increased to 18% after 3 hours of charging. The micro structure of the positive active materials was completely changed and the corrosion layer of the positive grid was less than $50{\mu}m$, regardless of the pressure of the safety valve after cycle life tests. The cause of discharge capacity decrease was found to be water loss and the shedding of the positive active materials. The pressure of safety valve does not give little effect to the cyclic performances and the failure modes of the gelled electrolyte valve-regulated lead acid batteries.

• Journal of Drive and Control
• /
• v.18 no.3
• /
• pp.8-15
• /
• 2021

A rear axle steering (RAS) system is attached to the rear of medium and large commercial vehicles that transport large cargo. The existing RAS systems are driven by electro-hydraulic actuator (EHA), and most commercialized EHAs consist of electric motors, hydraulic pumps, relief valves, prefill valves and cylinders. The prefill valve required for such EHAs is a type of check valve with extremely low cracking pressure that should not allow RAS to have noise or vibration, and the prefill valve prevents system negative pressure as well as unstable operation. Most papers on this topic rely on experiments to predict valve performance, and theoretically detailed modeling of valves or pipelines is performed, but it is very rare to evaluate hydraulic vibration characteristics by analysing everything from hydraulic pumps to valves comprehensively. In this study, we proposed an experimental circuit that can predict the performance of the prefill valve. The study also analysed the pressure-flow pulsation that is transmitted to the valve through the pipeline, and how the transmitted pressure-flow pulsation affects the valve vibration.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.505-508
• /
• 1995

This paper suggests new hydraulic circuit to control the pressure of clutches and brakes which has several advantages than conventional hydraulic circuit in automatic transmissions. In conventional hydraulic circuit, the pressures of all friction elements are controlled by only one pressure control valve and accumlators. So, controllable range is limited and it is unable to control the friction elements independently. Therefore, we can not do the fine control of timing between apply clutch and release clutch which is needed in clutch-to clutch shifting automatic transmissions. To overcome these faults, we designed the direct-acting hydraulic circuit where one pressure control valve and pressure control solenoid valve are allocated to each friction element and control that independently. Through this structural improvement of hydraulic circuit, we can achieve elaborate aontrol to clutch pressure. Specially, We can control the timing between apply clutch and release clutch delicately which is needed in clutch-to-clutch shifting.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.577-580
• /
• 1995

This paper suggests direct-acting hydraulic circuit to control clutches and brakes in automatic transmission. As only one pressure control valve controls the pressure of several friction elements with accumulators in conventional hydraulic circuit, the controllable range is limited. In addition, it is difficult to control the fine timing between apply clutch and release clutch. So, we designed new method to control the pressure of clutch which uses ressure control valve and pressure control solenoid valve independently in each friction element. through this structure improvement of hydraulic circuit, we can control the pressure of clutches and brakes finely and fine timing of between apply clutch and release clutch.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.7
• /
• pp.2853-2857
• /
• 2012

In this paper, 3-dimensional designing program, Solidwork was used in designing in order to investigate structure and characteristics of a pressure reducing valve which was used as an apparatus for keeping regulated pressure of water supply equipment system and also 2-dimensional drawing was made to manufacture a pressure reducing valve in the field.