Browsing by Subject "Valve"
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Item Design, Modeling, and Analysis of Microscale Pneumatic Valve Architectures to Simplify Integration of Small Displacement Actuators(2022-05) Hagstrom, NathanFluid power is an essential technology that underpins modern societal and industrial infrastructure. The performance of the majority of fluid power systems hinges on proper control valve function. Despite the importance, the core actuator technology used in control valves has remained largely unchanged for decades with incremental improvements made where possible. Now, conventional actuator technology development has reached a point of diminishing returns and provides a barrier to developing higher performance pneumatic systems. Use of smart materials in small displacement actuators, such as piezoelectric stack actuators, in control valves has the potential to break down barriers existing for conventional actuation methods. Piezoelectric stack actuators are useful as they have very low power consumption, nanometer displacement control resolution and microsecond response time. However, piezoelectric stack actuators are often overlooked due to inherent limitations in flow capacity created by their microscale actuator stroke. To enable revolutionary improvement in control valve design, this research answers fundamental questions required to enable widespread implementation of small displacement actuators, such as piezoelectric stacks, in proportional control valves. This research addresses limitations posed by existing pneumatic valve architectures through investigation of the potential for small displacement actuators use in applications where typically a relatively large displacement actuator would be needed. In so doing, this research investigates two methods for increasing flow capacity in valves using actuators with microscale stroke lengths. The first of two methods investigated uses a microfabricated array of micro-orifices to increase peripheral area acting as the governing flow restriction. The investigation involved design and characterization of a normally open axial proportional flow control valve using a piezostack actuator to modulate seal position. Further experimental and numerical study on the limitations posed when using an orifice array to increase flow area was summarily completed to develop an empirical basis for micro-orifice array design. The second of the two methods for increasing flow capacity was studied using experimental, numerical, and analytical methods. This method varied valve seal geometry to increase projected flow area and reduce viscous related flow losses. Results from study of the second method for increasing flow capacity enabled development of an analytical flow rate model to allow for model based valve design. Control valves better able to implement small displacement actuators, such as piezostack actuators, have potential to catalyze advances in numerous industries and applications. Impacted industries include: mobile robotics, medical instrumentation, natural gas handling, industrial control systems, and process control instrumentation. This research establishes a fundamental understanding of flow rate behavior in valves operating at microscale displacements. The valve architectures, empirical relationships, and flow models described provide a platform for future advances in control valve design and performance.Item Development of a MEMS Proportional Pneumatic Valve(2018-12) Hargus, AlexThe MEMS proportional pneumatic valve employs an array of micro-orifices paired with piezobender micro-actuators in parallel to achieve macro-flow rates. This design produces a miniature valve that is extremely fast, lightweight, compact, and efficient. This thesis describes the design, fabrication, and testing of a MEMS valve prototype. The prototype was able to achieve a maximum flow of 0.107 slpm at 0 V and a minimum flow of 0.038 slpm at 30 V, making the turndown ratio about 2.8 at a pressure of 0.69 bar. Operation requires very little power, and the entire valve is about the size of a dime. These findings signify a step forward on the path to employing these valves in fluid power systems, especially mobile applications, but also reveal the potential of this technology to improve upon these results.Item Enterococcus faecalis aggregation substance (Asc10) as liaison between bacterium and heart valve in endocarditis.(2009-08) Chuang-Smith, Olivia NewtonAggregation Substance proteins encoded by sex pheromone plasmids increase virulence of Enterococcus faecalis in experimental pathogenesis models, including infectious endocarditis. These large surface proteins may contain multiple functional domains involved in various interactions with other bacterial cells and with the mammalian host. Aggregation Substance Asc10, encoded by the plasmid pCF10, is induced during growth in the mammalian bloodstream, and pCF10 carriage gives E. faecalis a significant selective advantage in this environment. We employed a rabbit model to investigate the role of various functional domains of Asc10 in endocarditis. The data suggested that the bacterial load of the vegetation was the best indicator of virulence. Previously identified aggregation domains contributed to the virulence associated with the wild-type protein, and a strain expressing an Asc10 derivative where glycine residues in two RGD motifs were changed to alanines showed the greatest reduction in virulence. Remarkably this strain, and the strain carrying the pCF10 derivative with the in-frame deletion of prgB were both significantly less virulent than an isogenic plasmid-free strain. In addition, mutants carrying Tn917 insertions in the prgB gene demonstrated that secreted N-terminal Asc10 fragments possess activity promoting endocarditis virulence. The data demonstrate that multiple functional domains are important in Asc10-mediated interactions with the host during the course of experimental endocarditis, and that in the absence of a functional prgB gene, pCF10 carriage is actually disadvantageous in vivo. Since Asc10 is important as a virulence factor in E. faecalis endocarditis pathogenesis, developing immunization approaches against this surface protein will be useful in combating endocarditis disease. Use of Fab fragment antibodies against Asc10 was found to decrease vegetation size and bacterial load in the rabbit endocarditis model. In addition, microarray and histological studies revealed two routes of infection in vegetation formation; one in the absence of Asc10, characterized by a robust inflammatory response, and the second in which the presence of Asc10 dampens this response, possibly impeding the influx of immune cells into the vegetation. We also employed an ex vivo porcine heart valve adherence model to study the initial interactions between Asc10+ E. faecalis and valve tissue, and to examine formation of biofilms. We found that the aggregation domains contribute most to Asc10-mediated E. faecalis valve adherence, whereas the RGD motifs have importance in later stages of valve colonization. Again, an N-terminal Asc10 fragment expressed from a prgB Tn917 insertion mutant mediated adherence of E. faecalis cells, emphasizing the importance of the aggregation domains in valve attachment. Most of the Asc10 mutants examined showed some defects in valve adherence at 4 h, corroborating results from our rabbit endocarditis model, and implying that Asc10 contributes mainly to persistence of E. faecalis during endocarditis infection. Extracellular matrix (ECM) protein studies to determine the eukaryotic Asc10 ligand in valve tissue found that fulllength Asc10 protein did not mediate E. faecalis binding to vitronectin, fibronectin, fibrinogen, von Willebrand factor, heparan sulfate, or chondroitin sulfate. In scanning electron microscopy analysis of the infected valve tissue, we found evidence of biofilm formation, including growing aggregates of bacteria, and the increasing presence of exopolymeric matrix over time. Additionally, E. faecalis cells preferentially bound to damaged tissue, though it was difficult to determine whether the bacteria caused the damage, or if it was due to deterioration of the tissue over time. This porcine heart valve tissue colonization model will serve as a useful tool in future studies of biofilm formation.