Zero Leakage Research Articles

Modeling and Fault Simulation of a New Double-Redundancy Electro-Hydraulic Servo Valve Based on AMESim

The feedback spring rod of the armature assembly was eliminated in the double-redundancy electro-hydraulic servo valve (DREHSV), which employed a redundant design in contrast to the typical double-nozzle flapper electro-hydraulic servo valve (DNFEHSV). The pilot stage was mainly composed of four torque motors, and the double-system spool was adopted in the power stage. Consequently, the difficulty of spool displacement control was increased. By artificially changing the structural parameters of the simulation model in accordance with the theoretical analysis through AMESim, this paper aimed to study the dynamics and static characteristics of the DREHSV. The advantage of redundant design was further demonstrated by disconnecting working coils and setting the different worn parts of the spool. On the test bench, the necessary experiments were performed. Through simulation, it was discovered that when the clogged degree of the nozzle is increased, the zero bias value increases, the pressure and flow gain remain unchanged, and the internal leakage decreases. The pressure gain changes very little, the flow gain close to the zero position grows, the zero leakage increases significantly, and the pilot stage leakage changes very little as a result of the wear of the spool throttling edge. The basic consistency between the simulation curves and the experimental findings serve to validate the accuracy of the AMESim model. The findings can serve as a theoretical guide for the design, debugging, and maintenance of the DREHSV. The simulation model is also capable of producing a large amount of sample data for DREHSV fault diagnosis using a neural network.

Fluid Cavitation Intensity in Zero Leakage Upstream Pumping Face Seals with Spiral Grooves

Cavitation intensity variations in fluid lubrication may alter the mechanical and lubrication properties of the fluid. In this paper, a compressible cavitation model is presented to study the effect of fluid cavitation intensity on zero-leakage flow of upstream-pumping spiral grooves face seals (UPSGLFS). The pressure variation in cavities can be calculated considering the compressibility of the lubricating medium, the ratio of minimum pressure to cavitation pressure is further defined to characterize the cavitation intensity. A numerical analysis of the zero-leakage behavior of UPSGLFS is then performed based on its effect. Results show that cavitation plays a negative role in sealing performances. However, the groove’s configuration and working conditions have substantial effects on controlling the cavitation intensity. Meanwhile, whether a circumferential continuous pressure ring above the seal pressure can be formed is the design basis for judging the strict zero leakage of the medium, rather than only depending on the change of leakage rate parameter value. With suitable spiral groove parameter design, zero-leakage design for upstream-pumping seals may be achieved under multi-speed and multi-seal-pressure conditions. Here, a zero-leakage map is presented for working conditions with multi-speed ranging from 500 to 20,000[Formula: see text]rpm and multi-seal pressure ranging from 0.1 to 3.0[Formula: see text]MPa.

Design and Simulation of an O-type 3-position-4-way Directional Valve with Zero Leakage in the Mid-position

An O-type 3-position-4-way directional valve based on a pilot K-type spool valve and four B-type cartridge units with almost zero leakage in the mid-position is designed. Compared with an O-type3-position-4-way directional valve with an ordinary spool structure, under the same design requirements of nominal diameter, clearances, external load, etc., the mid-position leakage of the new valve is greatly reduced to nearly zero, that is, the new valve has excellent mid-position retention performance. The influence of fitting clearances between the pilot valve spool and valve sleeve (including uneven clearances), friction and check valve cracking pressure, etc. on the performance of the valve are analysed, and the results show that the factors mentioned above within reasonable values would hardly affect the mid-position retention performance of this new directional valve, and the occurrences of “crawling” and other phenomena could be reduced to a certain extent at the same time.

Design and Development of a Proficient Converter for Solar Photovoltaic Based Sustainable Power Generating System

The demand for renewable energy resources is invigorated due to various issues primarily related to energy security, energy sustainability, and greenhouse gas emissions. The proper utilization of renewable energy resources has certain challenges due to the varying nature of meteorological parameters and atmospheric aerosols. Therefore, it is of utmost importance to extract the maximum power from the photovoltaic systems with the help of proficient converters. Here, a coupled inductor based highly efficient synchronous interleaved boost converter is designed and developed for the grid integrated photovoltaic system. The proposed converter contains an Insulated Gate Bipolar Transistor (IGBT) switch in place of the conventional diode to maintain zero leakage current, bared minimum switching losses, and improved conduction time thereby enhancing the overall efficiency and reliability of the system. In addition, the proposed system topology is simple to implement and is capable of controlling power at both the generation as well as the load sides. The results obtained are validated with the help of a laboratory prototype under practical scenarios like varying temperature and solar irradiance. Further, an intelligent technique based on modified particle swarm optimization is utilized to extract the maximum power from the photovoltaic system. Moreover, the power quality indices were monitored and analyzed at the point of common coupling and at the grid level which vets the effectiveness of the proposed topology.

Cooling behaviors of a novel flow channel in mechanical seals of extreme high-speed rotation for cryogenic rockets

Mechanical seals usually require a special cooling system to control the high temperature generated by friction heating of rotating rings under the condition of extreme high-speed rotation. The working fluid is often in direct contact with the friction surface, and there is a risk of leakage. In the present paper, a novel cooling scheme driven by centrifugal force is proposed to cool the mating face in mechanical seals of turbopump in cryogenic rockets, which could achieve the absolute zero leakage of cooling fluid. To verify the flow feasibility and cooling effect of the new cooling structure, a three-dimensional numerical model is developed to predict the high-speed rotational flow and fluid–solid coupled heat transfer for liquid oxygen. The results show that the novel cooling scheme to cool the rotating ring II in the mechanical seal of cryogenic engines is reasonable and feasible, which could run itself relying on the radial centrifugal force, and could effectively control the temperature of the rotating ring II within the allowable range of the materials. This paper provides a new idea for cooling structure of mechanical seals in cryogenic rockets and numerical experience for ultra-high speed rotating flow and heat transfer with phase change.

Single-Phase Grid-Tied Transformerless Inverter of Zero Leakage Current for PV System

Multi-level transformerless inverters are widely used in grid-tied PV systems since they characterized by higher efficiency and lower cost. In this context, new topologies, modulation, and control schemes were presented to solve problems of a common-mode voltage and leakage current. This work proposes a transformerless five-level inverter with zero leakage current and ability to reduce the harmonic output content for a grid-tied single-phase PV system. The neutral of the grid links to a common on which the negative and the positive terminals of the DC-link are connected via parasitic capacitors that can eliminate the leakage current. The proposed topology, with its inherent circuit structure, leads to boost the overall efficiency. Simulation and experimental results show almost zero leakage current and a high-quality output when maintaining balanced capacitor voltages on the DC-link input. The experimental results show 1.07% THD and 96.3 % maximum efficiency when injecting a power of 1.1 kW that verify the performance of the proposed inverter with PV sources.

Zero leakage? Landfill liner and capping systems in Germany

An approach to achieve ‘zero leakage’ is discussed with respect to experience in Germany, where strict regulations for landfill lining and capping systems have been developed and issued because of large environmental problems related to landfills that accumulated in the 1970s and 1980s. Using a thick, high-quality high-density polyethylene (HDPE) geomembrane (GM) that is installed free of residual waves and wrinkles in intimate contact with a compacted clay liner or geosynthetic clay liner of very low permeability, by a qualified, experienced, well-equipped and properly third-party-controlled installer, and which is protected by heavy protection layers designed with respect to the long-term performance of the GM may result in a liner or capping system of practically no leakage. This is demonstrated by analysing results of measurements obtained from permanently installed leak-detection systems in combination with HDPE GMs. The survey was based on 32 German landfills with 1 276 500 m2 of installed GMs.

Influence of Particle Size Distribution of Magnetic Fluid on the Resistance Torque of Magnetic Fluid Seal

Magnetic fluid seal is widely used in military and aerospace industry owing to its zero leakage property, long life and reliability. The resistance torque is often required to be small and stay within allowable scope with the standing time expanding and the working environment changing. In this paper, we discussed the influence of the particle size distribution of magnetic fluid on the resistance torque of magnetic fluid seal. Samples of magnetic fluid of different particle size distribution were processed by applying a magnetic field gradient. Afterwards, the rheological property of different samples was analyzed using rheometer. Besides, the resistance torque of magnetic fluid seal on different occasions was measured. We explained these results from the point of formation and destruction of magnetic aggregations based on the theory of magnetoviscous effect, thus provided feasible ways to improve the performance of magnetic fluid seal.

Optimized Quantization in Zero Leakage Helper Data Systems

Helper data systems are a cryptographic primitive that allows for the reproducible extraction of secrets from noisy measurements. Redundancy data called helper data makes it possible to do error correction while leaking little or nothing (Zero Leakage) about the extracted secret string. We study the case of non-discrete measurement outcomes. In this case, a quantization step is required. Recently, de Groot et al. described a generic method to perform the quantization in a Zero Leakage manner. We extend their work and show how the quantization intervals should be set to maximize the amount of extracted secret key material when noise is taken into account.

Designing Low Power and Durable Digital Blocks Using Shadow Nanoelectromechanical Relays

Nanoelectromechanical (NEM) relays are a promising emerging technology that has gained widespread research attention due to its zero leakage current, sharp ON-OFF transitions, and complementary metal–oxide–semiconductor compatibility. As a result, NEM relays have been significantly investigated as highly energy-efficient design solutions. A major shortcoming of NEMs preventing their widespread use is their limited switching endurance. Hence, in order to utilize the low-power advantages of NEM relays, further device, circuit, and architectural techniques are required. In this paper, we introduce the concept of shadow NEM relays, which is a circuit-level technique to leverage the energy efficiency of the NEM relays despite their low switching endurance. This technique creates two virtual ground nodes in a block to allow: 1) a low power mode with functional NEM relays and 2) a normal mode with failed NEM relays. To demonstrate the applicability of this concept, we have applied it to a six-transistor SRAM cell as an illustrative example. We also investigate the applicability of this SRAM cell in field-programmable gate arrays and on-chip caches. Experimental results reveal that shadow NEM relays can reduce the power consumption of SRAM cells by up to 80% while addressing the limited switching endurance of NEM relays.

Radiation-Hardened Design of Nonvolatile MRAM-Based FPGA

Field-programmable gate arrays (FPGAs) based on static random access memory (SRAM) are more common than other types, including flash and anti-fuse, because of their infinite configurability and high performance. However, following the scaling down of CMOS technology, standby power of the CMOS circuits are becoming crucial. Logic circuits based on magnetic RAM (MRAM) can be an attractive replacement for SRAM-based logics thanks to their zero leakage and CMOS compatibilities. Furthermore, in FPGA design, using MRAM logics instead of SRAM logics results in some more advantages including non-volatility and high radiation reliability. In this paper, effects of radiation-induced soft errors on MRAM-based FPGAs (MFPGAs) are taken into account. Soft error tolerance of the previous MFPGAs are discussed and a new MFPGA structure is proposed. It is shown that the proposed non-volatile, low-power, and high-speed MFPGA is highly robust against radiation-induced soft errors. It is also shown that the proposed MFPGA offering a high radiation robustness does not incur a considerable design overhead compared with the other similar MFPGAs.

Quantization in zero leakage helper data schemes

A helper data scheme (HDS) is a cryptographic primitive that extracts a high-entropy noise-free string from noisy data. Helper data schemes are used for preserving privacy in biometric databases and for physical unclonable functions. HDSs are known for the guided quantization of continuous-valued sources as well as for repairing errors in discrete-valued (digitized) sources. We refine the theory of helper data schemes with the zero leakage (ZL) property, i.e., the mutual information between the helper data and the extracted secret is zero. We focus on quantization and prove that ZL necessitates particular properties of the helper data generating function: (1) the existence of “sibling points”, enrollment values that lead to the same helper data but different secrets and (2) quantile helper data. We present an optimal reconstruction algorithm for our ZL scheme, that not only minimizes the reconstruction error rate but also yields a very efficient implementation of the verification. We compare the error rate to schemes that do not have the ZL property.

Zero Leakage Sealings for Reciprocating Compressors

AbstractThe piston rod of a reciprocating compressor is sealed with elastic cylindrical sealing elements. Across the sealings the pressure drops from the operating pressure to the ambient pressure. The lubrication gap between the elastic sealing and reciprocating piston rod is studied with the aim to find conditions of a leakage free sealing. The flow in the lubrication gap and the elastic deformation of the sealing are determined simultaneously. The netflow during one cycle of the reciprocating piston rod is calculated. It turns out that maintaining zero leakage is very sensible. Indeed the outbound flow during out‐stroke has to be equal the inbound flow during the instroke. By prescribing a special shape of the undeformed sealing zero leakage can be attained — at least theoretically for certain operating conditions. It turns out that temperature dependent material data and a model for cavitation is necessary. The model, its numerical implementation and results will be discussed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compliance to ATEX and API685 for sealless pumps

Canned motor pumps for handling hazardous substances combine the full ATEX compliance with Fugitive Emission Regulations due to their zero leakage design. Dieter Lau of Hermetic Pumpen GmbH discusses the implications of ATEX and API685 for sealless pumps.

On the energy approach to the theory of coupled inductors

AbstractThe paper presents a revisited energy approach to the theory of a set of n coupled inductors. The hybrid constitutive relations are analyzed. It is shown that the fundamental relation expressing the energy of the system requires a minimum number of coupling terms if a set of hybrid independent variables is adopted. The hybrid independent variables also allow to represent singular systems having zero magnetizing energy or zero leakage field energy, or both, and to give a rigorous definition of the ideal transformer. Exact equivalent networks of both two‐ and three‐winding transformers are presented.

The influence of the surface roughness on the specific leak rate of gasket seals

By using the concepts developed in Sealography, an equation for calculating the specific leak rate of vacuum ga sket seals is derived. The equation, which is found to be in good agreement with experimental data published by various authors, shows that the specific leak rate (expressed in terms of leak rate width/length of seal) is given by the product between the sealing coefficient, the square of the initial surface roughness, and the pressure difference across the seal. Graphs for establishing the value of the sealing coefficient and specific leak rate are presented, and the im itations due to the surface roughness in obtaining “Zero leakage” are analyzed.

679. Zero leakage effort for Saturn vehicles: H Bergeler, Conf Design of Leak-tight Separable Fluid Connectors, Rep NASA-TM-X-60234, March 1964, 3–28 ( Sci Tech Aerospace Reps, 5 (21), 3856, N67-35569)

679. Zero leakage effort for Saturn vehicles: H Bergeler, Conf Design of Leak-tight Separable Fluid Connectors, Rep NASA-TM-X-60234, March 1964, 3–28 ( Sci Tech Aerospace Reps, 5 (21), 3856, N67-35569)

Zero Leakage: Results of an Advanced Lip Seal Technology

The advent of the “Helixseal,” a type of hydrodynamic sealing element, to the automotive industry has provided a means for greatly reducing sealing problems with very little increase in production cost. A new sealing technology, developed during a 10-year program at the General Motors Research Laboratories, has involved detailed studies to optimize the basic sealing parameters of radial lip-type seals. Although all elements of a conventional lip seal design can be optimized, the frequency of seal failure is still intolerable due to the large number of production variables which affect leakage. Consequently, it was necessary to explore and develop a means of complementing the lip seal, whereby increased reliability could be assured. The Helixseal is based upon hydrodynamic principles which allow the generation of controlled fluid forces. It consists of angular pumping vanes, applied to the seal face to provide a viscous shear force that opposes leakage of the fluid film. Optimized design of the Helixseal can assure zero leakage in seal applications.