Valve Gap Research Articles

Air Suction Characteristics of a Water Hydraulic Piston Pump With Check Valves

The purpose of this paper is to investigate the air suction characteristics of a water hydraulic piston pump with check valves. The influence of some factors on its air suction performance, including compression ratio, initial spring forces, valve gaps, etc., was simulated. The real suction height of the pump prototype was tested and it agreed well with the simulation result. The compression ratio and the outlet pressure of the pump have been found to be dominant. This study can provide a guide for the design of a piston pump whose air suction characteristics need to be considered in application.

Acquisition of physical dormancy and ontogeny of the micropyle–water-gap complex in developing seeds of Geranium carolinianum (Geraniaceae)

The 'hinged valve gap' has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slow-drying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a 'micropyle--water-gap complex'.

Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to Geranium carolinianum

Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum. Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments. Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the 'hinged valve' (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. the morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium. Dislodgment of swollen 'hinged valve' palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap ('hinged valve gap') differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.

Hydro- and thermodynamics of the subcavitation breakup of emulsions in the valve gap of a homogenizer

The hydrodynamic features of valve homogenizers for the mechanical treatment of emulsions (breakup of dispersion medium) are considered. Distributions of the hydro- and thermodynamic characteristics of flow are derived based on the hypothesis of the discreteness of the liquid phase. The existence of ultralow-pressure zones in the cavitation regions is theoretically proven. The thermodynamic characteristics of emulsion drops in an ultralow-pressure zone are tentatively calculated.

Passive MEMS Valves With Preset Operating Pressures for Microgas Analyzer

In this paper, we present integrated disk-in-cage poppet valves with tuned spring stiffness for gas flow control of a microgas analyzer. The valves require zero power and close at preset offset pressures (0-35 psig) to switch from gas sample loading onto a preconcentrator to concentrated constituent sample injection into a microgas chromatograph. Air flow rates of 4.5 mL/min at pressures of - 2.5--5 psig (vacuum sample loading) were measured. Hydrogen leak rates of 0.1 muL/s (0.006 mL/min) were measured with valves closed at 15 psig. Analytical and numerical modeling was used to guide design of valve spring constants (ranging from 10 to 1500 N/m) that control the valve open position, flow rate, and closing pressure. The parameter design space is limited to a range of seat overlap, valve size, and spring stiffness that will allow adequate flow rate, sealing, and closing at predictable pressures. A linear curve defining closing pressure as a function of spring constant, valve gap, valve size, and seat overlap fit measured closing pressure data and can be used to predict closing pressure for future designs.

Low intake valve lift in a port fuel-injected engine

Abstract A phenomenological study of the airflow and fuel spray interaction in a variable valve gasoline engine is presented. Experiments were performed in a steady-state flow rig fitted with a modified production cylinder head. The intake valve lift was varied manually. The mass flow rates of air and fuel through the test rig were adjusted to match typical engine operating conditions. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) measurements of the airflow showed the breakdown of a single, forward tumbling vortex-like structure into a pair of high-speed, turbulent jets at low valve lifts. Two transitional phases in the flow at the valve gap were identified for valve lifts less than 1.5 mm and greater than 3 mm. At the lower limit, a jet flapping instability was recorded. A port fuel injector (PFI) spray was characterised in a quiescent, chamber and within the test rig. High Speed Photography (HSP) and Phase Doppler Anemometry (PDA) were used to measure the effects of varying valve lift upon the fuel droplet characteristics. The in-cylinder measurements showed a reduction in mean droplet diameter of up to 50%, close to the valve gap, for peak valve lifts of less than 3 mm.

1737 圧力式乳化機の内部流れと乳化作用の研究(S19-7 流体機械に関連した流動現象とその解析・計測(7)流体機械に関連した諸問題,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Homogenizer is a key unit operation used to disrupt fat globules or cells containing intracellular bioproducts. Modeling and optimization of a small homogenizing unit are often restrained by a lack of information on the flow conditions within the homogenizer valve. An investigation of the impinging radial jet within a homogenizer valve is presented. An experimental measurement of the size of the valve gap is presented in order to validate mathematical relations that give valve gap sizes versus homogenizing pressure. The modeling results give information on the mechanical stress and the shear rates in small disruption valves.

Experimental Identification of the Dead Zone in Proportional Directional Pneumatic Valves

This work presents a new methodology for dead zone nonlinearity identification in proportional directional pneumatic valves. It is based on observing the dynamic behaviour of the pressure in the valve gaps. Dead zone is common in hydraulic and pneumatic valves because the spool blocks valve orifices with some overlap, so that for a range of spool positions there is no fluid flow. The dead zone nonlinearity is a key factor that limits both static and dynamic performance in feedback control of fluid power systems. The usual method to cancel the harmful effects of dead zone is to add its fixed inverse function into the controller. This inverse is modelled by a set of parameters that need to be identified. The classic dead zone parameter identification uses expensive flow transducers and special test rig, while our proposed methodology needs only pressure transducers. Experimental results illustrate the efficacy of this methodology that is cheaper and faster.

Spatial flow velocity distribution around an inlet port/valve annulus

An experimental investigation of the airflow through inlet port of a standard production direct injection diesel engine is presented. The investigation comprises mass flow rate and pressure drop measurements at fixed valve lifts, and spatial distributions of mean and r.m.s. velocity components around the port/valve annulus measured under steady flow conditions by special designed miniature hot-wire anemometer X probe. The results show that the velocity field is distributed non-uniformly across the valve gap and around valve periphery. Nonuniformity is more expressed at higher valve lifts. Flow instability in a jet leaving the port (jet flapping) is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. The presented experimental method, based on the application of miniature multiple hot-wire probes, makes possible investigation of flow performances of an inlet port and poppet valve assembly of a production engine head without any modification for ensuring an optical access within the port/cylinder.

New Method for Comparing Flow in Spring-Loaded Valves

Spring-loaded valves possesses a dynamic operating range, in which the moving element is balanced by the flow and the spring forces. This feature means that the valve performance, including the pressure drop coefficient and the valve gaps, cannot be fully described only by using the Reynolds number without considering the spring properties. In this article, the theoretical analysis of the flow in spring-loaded valves was made to unify the flow and the spring forces. A new dimensionless number named the Zhang number was defined, with which the valve gaps and thus the pressure drop coefficient in the dynamic operating range can be clearly described. The similarity of flows in the valve loaded by different spring sets is then ensured. The significance of this similarity has been excellently demonstrated by an industrial compressor valve. Specifically, once a valve loaded by a set of springs is characterized, the valve characteristics using other spring sets can be directly obtained from the existing characteristic. No additional calibration of valve flows is necessary.

Initial Opening of a Compressor Valve

AbstractThe initial opening of a compressor valve is investigated. The motion of the valve plate is essentially determined by the pressure distribution in the valve gap. Since the initial gap is extremly narrow a conventional CFD solution fails. Therefore the initial stages of the opening process are modelled by using an asymptotic expansion with respect to a small asepct ratio of the valve gap. The purpose of the analysis is to provide an initial condition for a CFD simulation of the valve dynamics. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Parametric study on the fuel film breakup of a cold start PFI engine

In order to provide more insight on improving the cold start fuel atomization for reducing unburned hydrocarbon emissions, the liquid fuel film breakup phenomenon in the intake valve/port region was investigated in depth for port-fuel-injected engines. Experiments were conducted using high-speed high-resolution imaging techniques to visualize the liquid film atomization and airflow patterns in an axisymmetric steady flow apparatus. The impact of valve/port seat geometry, surface roughness, and fuel properties on airflow separation and fuel film breakup were determined through a parametric study. CFD simulations were also performed with FLUENT to help understand the airflow behavior inside the intake port and valve gap region and its potential impact on fuel film atomization.

Analysis of a new type of high pressure homogeniser. Part B. study of droplet break-up and recoalescence phenomena

Calculation of the flow pattern in a new small homogenising valve design (Stansted, U.K.), able to reach operating pressure as high as 350 MPa , was investigated in the first part of this paper using a Computational Fluid Dynamics method. Numerical simulation results are used in the present paper to better understand the emulsification process in the Stansted high-pressure homogeniser. Deformation of drops is supposed to occur in the intense elongational flow caused by the restriction between the piston and the seat of the valve. Deformation may be mainly followed by drop disruption in the narrow valve gap. Break-up probably also occurred in the highly turbulent region, located just at the exit of the gap, and underlined by the numerical investigation. Cavitation and the rate of recoalescence, first assumed from numerical results, are determined thank to experimental methods. Intensities of both phenomena strongly increase with homogenising pressure. Final droplet size of model oil-in-water emulsions is then the result of equilibrium between droplet break-up and recoalescence, which strongly depends on operating pressure.

Analysis of a new type of high pressure homogeniser. A study of the flow pattern

High-pressure homogenisation is a key unit operation used to disrupt fat globules or cells containing intracellular bioproducts (AIChE J. 43(4) (1997) 1100). Modelling and optimisation of a small homogenising unit are often restrained by a lack of information on the flow conditions within the homogeniser valve. A numerical investigation of the flow within such a new homogenising valve, capable to reach pressure as high as 350 MPa (Stansted Fluid Power Ltd, UK) is presented. Results are obtained using the finite-volume technique and a RNG k– ε turbulence model with low Reynolds number near wall treatment conditions. An experimental measurement of the size of the valve gap is presented in order to validate mathematical relations that give valve gap sizes versus homogenising pressure. The modelling results give detailed information on the mechanical stresses and the high shear rates in small disruption valves, and also reveal other phenomena that could not be easily determined experimentally.

A silicon-chip-based light valve with reflective twisted-nematic mode for high-definition projectors

— Crystalline-silicon-chip-based reflective light valves are suitable for realizing high definition and bright liquid-crystal projectors. We have developed an XGA (1025 × 769 pixels) silicon-chip-based light valve with a diagonal display area of 2.54 cm (1 in.). The reflective twisted-nematic mode was examined by using the Jones matrix method as a display mode, and the normally white reflective twisted-nematic mode was selected. This mode is suitable for a narrow cell gap, and a fast response time can be expected. In addition, the driving voltage of this mode is low and has good chromaticity with small retardation. The cell gap of the light valve is 2 μm. The cell gap support is made using spacer posts formed on the silicon chip with a photodefinable resin. The response time is 12 msec, including both rise and fall times. The contrast ratio is more than 1000 at 5 Vrms.

Gaulin homogenization: a mechanistic study.

Free radical-based oxidation has been detected in the normal operating regime of the Gaulin homogenizer, demonstrating that cavitation occurs in this important industrial bioprocessing equipment. Free radical generation is suppressed by imposition of back pressure, proving that such cavitation occurs in the impingement section. The calculated value of the cavitation number is consistent with submerged jet cavitation, wherein a high-speed jet exiting from the valve gap accelerates fluid in the impingement region, creating the vacuum conditions for cavitation. Using polysaccharides as a model shear-sensitive compound, their breakage pattern in the homogenizer was characterized by molecular size and polydispersity and compared to those of fluid shear flows in capillary tubes and cavitating flow from a sonic horn. The results indicate that breakage occurs primarily by fluid shear, although a contribution by cavitation is also apparent when back pressure is applied. Because biological molecules can readily react with free radicals and the alterations caused thereby are subtle in nature, a thorough evaluation of the impact of free radicals in upstream homogenization is warranted.

EXPERIMENTAL STUDY OF FLOW IN THE GAP OF NEEDLE VALVE

Needle valve is widely used for flow control in industry. Changing the flow area, which is a circular gap between the cone-shaped core and valve body, the discharge of flow through the needle valve can be controlled. The gap of needle valve is less than one hundred microns, which can be blocked up slowly by the tiny particles in the fluid for a long time. In this paper the quantitative relations among the reduction of discharge, size of particle, concentration of particle and opening of needle valve were studied. These results are worth for designing a new style lubricator with high precision. The particle's movement in the narrow slit was also' analyzed in theory and visualization.

98/04072 Flow separation in the inlet valve gap of piston engines

98/04072 Flow separation in the inlet valve gap of piston engines

The effect of swirl on the annular flow past an axisymmetric poppet valve

This paper describes an experimental investigation of the swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions. This work is an extension of the preceding paper, which is a study of the non-swirling flow in the same flow configuration [1]. Three different swirl rates were investigated with the aim to study the effects of swirl on the mean flow and turbulence characteristics of the flow field. The flow structure was studied by means of laser sheet flow visualization and the three velocity components and the associated Reynolds stresses were measured by ensemble-averaged laser Doppler anemometry techniques. The results are compared with those obtained with the non-swirling flow. The addition of the swirl was found to alter the flow structure, particularly below the valve where a new counter-rotating vortex is formed. A toroidal recirculation zone is also formed in the valve passage. The growth and entrainment of the jet emanating from the valve gap increase and its trajectory angle changes. The flow visualization studies showed evidence of precession of the swirl centre and jet flapping. Swirl increases the Reynolds stresses and the turbulence production rate in most regions of the flow.

The correlation of cell disruption with homogenizer valve pressure gradient determined by computational fluid dynamics

Numerical investigations of the flow and pressure fields within a homogenizer valve have been conducted using the computational fluid dynamics code, PHOENICS 2.1. Results are obtained for two valve seat designs over a range of valve gaps. The dependence of valve gap on operating pressure is measured experimentally and compares well with numerical predictions. A simple expression that uses the numerical results and allows ready calculation of pressure gradient from homogenizer operating and design conditions is presented. Pressure gradient is shown to be a better independent variable for correlating cell disruption than operating pressure over a wide range of operating and design parameters.