Pressure Relief Valve Research Articles

Analysis on transient piping pressure and force caused by high pressure steam flow disturbances

This paper presents a quantitative analysis on transient responses of pressure and its resulting force to sudden operation of a pressure relief valve on the main steam line of a pressurized water reactor plant, which is initially in a closed system at high pressure. When the valve at closed position changes to the full open position suddenly, the shock can be generated by the sudden steam flow which may reach critical velocity and then travel through the pipe line causing some damages to the piping system. The major characteristics of shock are quantitatively investigated on the basis of one dimensional pressure wave theory. Through the application to the actual transient incident occurred at the Kori unit 1 on 16 April 2005, it is found that the present approach is quite practical to predict the transient behavior of shocks caused by sudden operation of valves.

The Value of Simulation Training during Anesthesia Residency

Stanford University School of Medicine, Stanford, California. geoffl@stanford.eduIt is hard to measure the intangibles of skilled anesthesia management such as leadership, planning, and dynamic problem solving, let alone to link them unequivocally to specific patient outcomes. Although simulation training has been advanced as a method to help develop crisis management and other “nontechnical” skills, proof of this link is currently incomplete.1–3However, a recent example may highlight the value of simulation training during anesthesia residency with respect to these issues. On a recent international medical trip, the operating room's sole oxygen supply, an H-cylinder, was accidentally knocked over, severely damaging its regulator and causing a high-pressure leak necessitating its immediate removal. Because oxygen was the only gas supplied to the anesthesia machine, all fresh gas flow to the anesthetized and paralyzed patient ceased, and the oxygen supply alarm sounded.Options at this point included (1) hand ventilation through the circuit (taking advantage of a functional carbon dioxide–absorbing system), but diluting the alveolar anesthetic level and risking wastage of oxygen through small leaks in the circuit, or (2) apneic oxygenation from a quiescent circuit. The latter was chosen, because it would be the means most likely to maintain alveolar anesthetic and oxygen levels while freeing hands to prepare for an intravenous anesthetic. Accordingly, further ventilation was temporarily suspended, and the sidestream carbon dioxide sampling line was disconnected and capped (so as not to waste oxygen from the circuit). Fortunately, a pulse oximeter was available.The personnel management of this situation focused on dispatching others to obtain a self-inflating ventilation bag from the recovery room (the one and only such device in the entire hospital) and making preparations for an intravenous anesthetic, while seeking a replacement for the damaged oxygen pressure regulator. In this particular event, the patient experienced 6–7 min of apnea and remained anesthetized while maintaining oxyhemoglobin saturations of 100%.When faced with an oxygen supply loss, the near explosion of an unsecured cylinder, and a loud alarm, one's first instinct may be to vigorously ventilate the patient. However, by closing the pressure relief valve and discontinuing sidestream carbon dioxide analysis, one can ensure a 4- to 15-min oxygen supply (depending on fraction of inspired oxygen, functional residual capacity, and patient metabolism). It is not clear how long it would have taken to sort through these options from first principles under these difficult conditions without previous exposure to a similar problem during a crisis simulation course in residency (Anesthesia Crisis Resource Management, Stanford University School of Medicine, Stanford, California).4–6In this course, trainees manage both common and novel operating room complications, allowing them to develop templates for technical and behavioral responses to such situations. The use of high-fidelity human patient simulators and recreated operating room environments in courses such as this capture both the stress and the immediacy of real patient emergencies and, ideally, provide the first exposure to plausible catastrophes in a setting where no patients' lives are at risk. When a potentially catastrophic oxygen supply failure arose in real life, its management seemed relatively routine because, virtually speaking, I'd been there before.Stanford University School of Medicine, Stanford, California. geoffl@stanford.edu

Research on low cavitation in water hydraulic two-stage throttle poppet valve

Cavitation has important effects on the performances and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Two-stage throttle valve is a practicable configuration to mitigate cavitation, which is extensively used in water hydraulic pressure relief valves and throttle valves. The pressure distribution inside a medium chamber located between two throttles of a two-stage throttle valve is investigated through numerical simulations. The effects of the passage area ratio of the two throttles and the inlet and outlet pressures on the pressure inside the medium chamber are examined. The simulation results indicate that (a) the pressure inside the medium chamber is not constant, (b) the locations of maximum and minimum pressures inside the medium chamber are both fixed, which will not vary with the passage area ratio or the inlet and outlet pressures, and (c) the ratio of the pressure drop across the front throttle to the total pressure drop across the two-stage throttle valve is nearly constant. The critical cavitation index of the two-stage throttle valve is then established. A semiempirical design criterion is obtained for the water hydraulic two-stage throttle valve. The correlation between the critical cavitation index and the passage area ratio of the two throttles is investigated. Relevant validation experiments are conducted at a custom-manufactured testing apparatus. The experimental results are consistent with the simulated ones. Further analyses indicate that (a) the large backpressure can improve not only the anti-cavitation capability but also the total load rigidity of the water hydraulic two-stage throttle valve, (b) an appropriate passage area ratio will be beneficial for improving the anti-cavitation capability of the water hydraulic two-stage throttle valve, and (c) the water hydraulic two-stage throttle valve with a passage area ratio of 0.6 would have the best anti-cavitation performance with the lowest risk of cavitation.

Pressure control of PEMFC distributed power generator

Control design is important for PEMFC (proton exchange membrane fuel cell) distributed power generator to satisfy user requirement for safe and stable operation. For a complex multi-variable dynamic system, a dynamic simulation model is first established. In view of close coupling and non-linear relationships between variables, the intelligent auto-adapted PI decoupling control method is used. From the simulation results it is found that, by bringing quadratic performance index in the single neuron, constructing adaptive PI controller, and adjusting gas flow rates through the second pressure relief valve and air compressor coordinately, both anode and cathode pressures can be maintained at ideal levels.

Measurement and study of the distributing law of in-situ stresses in rock mass at great depth

To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths (over 1000 m) in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.

On the Transition From Non-BLEVE to BLEVE Failure for a 1.8M3 Propane Tank

A series of fire tests were conducted on nine, 1.8m3(500USgal) ASME code propane pressure vessels to study the significance of pressure relief valve behavior on tank survivability to fire impingement. In these tests three tanks ruptured (i.e., finite failure) and six boiling liquid expanding vapor explosion (BLEVEd) (total loss of containment). The difference between the BLEVE and non-BLEVE failures was due to a difference in the fire conditions. It is believed that these tests show some insight into the BLEVE process. In all tests the fire consisted of an array of nominal 590kW(2MBTU∕h) liquid propane burners. A pool fire was not used because of the uncontrolled nature of open pool fires. It was believed that very repeatable fire conditions could be achieved by using a series of burners. In the tests where the outcome was a non-BLEVE there were two burners mounted 30cm above the tank on the tank vapor space. These burners were used to weaken the steel and to initiate a failure. To heat the liquid, there were between 4 and 12 burners applied below the liquid level. When one burner was added on the vapor space, all of the remaining tanks BLEVEd. This was true over a range of fill levels (at failure) of between 10% and 50% by volume. It is believed this added burner was just enough to weaken the tank so that any initial rupture would grow towards a total loss of containment and BLEVE. This paper presents the details of this test series and shows how severely heated length and liquid energy affected the outcome.

The Effect of Pressure Relief Valve Blowdown and Fire Conditions on the Thermo-Hydraulics Within a Pressure Vessel

In the summers of 2000 and 2001, a series of controlled fire tests were conducted on horizontal 1890liter (500 US gallon) propane pressure vessels. The test vessels were instrumented with pressure transducers, liquid space, vapor space, and wall thermocouples, and an instrumented flow nozzle in place of a pressure relief valve (PRV). A computer controlled PRV was used to control pressure. The vessels were heated using high momentum, liquid propane utility torches. Open pool fires were not used for the testing because they are strongly affected by wind. These wind effects make it almost impossible to have repeatable test conditions. The fire conditions used were calibrated to give heat inputs similar to a luminous hydrocarbon pool fire with an effective blackbody temperature in the range of 850°C±50°C. PRV blowdown (i.e., blowdown=poppressure−reclosepressure) and fire conditions were varied in this test series while all other input parameters were held constant. The fire conditions were varied by changing the number of burners applied to the vessel wall areas wetted by liquid and vapor. It was found that the vessel content’s response and energy storage varied according to the fire conditions and the PRV operation. The location and quantity of the burners affected the thermal stratification within the liquid, and the liquid swelling (due to vapor generation in the liquid) at the liquid∕vapor interface. The blowdown of the PRV affected the average vessel pressure, average liquid temperature, and time to temperature destratification in the liquid. Large blowdown also delayed thermal rupture.

On the Modeling of Hydraulic Components in Rotorcraft Systems

A physics based methodology for modeling of hydraulic devices within multibody-based comprehensive models of rotorcraft systems is developed. The proposed models are developed in two stages. At first, models are developed for three basic hydraulic elements: the hydraulic chamber, the hydraulic orifice and the pressure relief valve. These models consist of nonlinear differential equations involving empirical parameters. Next, these basic elements are combined to yield device models for linear hydraulic actuators, simple hydraulic dampers, and hydraulic dampers with pressure relief valves. The proposed hydraulic device models are implemented in a multibody code and calibrated by comparing their predictions with test bench measurements for the UH-60 helicopter lead-lag damper. While predicted peak damping forces are found to be in good agreement with measurements, the model does not predict the entire time history of damper force to the same level of accuracy. The validated model of the UH-60 lead-lag damper model is coupled with a comprehensive model of the vehicle. Measured aerodynamic loads are applied to the blade and predicted damper forces are compared with experimental measurements. A marked improvement in the prediction is observed when using the proposed model rather than a linear approximation of the damper behavior.

Study of solar energy powered transcritical cycle using supercritical carbon dioxide

In this paper, the performance of solar energy powered transcritical cycle using supercritical carbon dioxide for a combined electricity and heat generation, is studied experimentally. The experimental set-up consists of evacuated solar collectors, pressure relief valve, heat exchangers and CO2 feed pump. The pressure relief valve is used to simulate operation of a turbine and to complete the thermodynamic cycle. A complete effort was carried out to investigate the cycle performances not only in summer, but also in winter conditions. The results show that a reasonable thermodynamic efficiency can be obtained and COP for the overall outputs from the cycle is measured at 0.548 and 0.406, respectively, on a typical summer and winter day. The study shows the potential of the application of the solar energy powered cycle as a green power/heat generation system. Copyright © 2006 John Wiley & Sons, Ltd.

Estimation of airway obstruction using oximeter plethysmograph waveform data

BackgroundValidated measures to assess the severity of airway obstruction in patients with obstructive airway disease are limited. Changes in the pulse oximeter plethysmograph waveform represent fluctuations in arterial flow. Analysis of these fluctuations might be useful clinically if they represent physiologic perturbations resulting from airway obstruction. We tested the hypothesis that the severity of airway obstruction could be estimated using plethysmograph waveform data.MethodsUsing a closed airway circuit with adjustable inspiratory and expiratory pressure relief valves, airway obstruction was induced in a prospective convenience sample of 31 healthy adult subjects. Maximal change in airway pressure at the mouthpiece was used as a surrogate measure of the degree of obstruction applied. Plethysmograph waveform data and mouthpiece airway pressure were acquired for 60 seconds at increasing levels of inspiratory and expiratory obstruction. At each level of applied obstruction, mean values for maximal change in waveform area under the curve and height as well as maximal change in mouth pressure were calculated for sequential 7.5 second intervals. Correlations of these waveform variables with mouth pressure values were then performed to determine if the magnitude of changes in these variables indicates the severity of airway obstruction.ResultsThere were significant relationships between maximal change in area under the curve (P < .0001) or height (P < 0.0001) and mouth pressure.ConclusionThe findings suggest that mathematic interpretation of plethysmograph waveform data may estimate the severity of airway obstruction and be of clinical utility in objective assessment of patients with obstructive airway diseases.

Compressed Natural Gas Bus Safety: A Quantitative Risk Assessment

This study assesses the fire safety risks associated with compressed natural gas (CNG) vehicle systems, comprising primarily a typical school bus and supporting fuel infrastructure. The study determines the sensitivity of the results to variations in component failure rates and consequences of fire events. The components and subsystems that contribute most to fire safety risk are determined. Finally, the results are compared to fire risks of the present generation of diesel-fueled school buses. Direct computation of the safety risks associated with diesel-powered vehicles is possible because these are mature technologies for which historical performance data are available. Because of limited experience, fatal accident data for CNG bus fleets are minimal. Therefore, this study uses the probabilistic risk assessment (PRA) approach to model and predict fire safety risk of CNG buses. Generic failure data, engineering judgments, and assumptions are used in this study. This study predicts the mean fire fatality risk for typical CNG buses as approximately 0.23 fatalities per 100-million miles for all people involved, including bus passengers. The study estimates mean values of 0.16 fatalities per 100-million miles for bus passengers only. Based on historical data, diesel school bus mean fire fatality risk is 0.091 and 0.0007 per 100-million miles for all people and bus passengers, respectively. One can therefore conclude that CNG buses are more prone to fire fatality risk by 2.5 times that of diesel buses, with the bus passengers being more at risk by over two orders of magnitude. The study estimates a mean fire risk frequency of 2.2 x 10(-5) fatalities/bus per year. The 5% and 95% uncertainty bounds are 9.1 x 10(-6) and 4.0 x 10(-5), respectively. The risk result was found to be affected most by failure rates of pressure relief valves, CNG cylinders, and fuel piping.

The Effect of Reduced Design Margin on the Fire Survivability of ASME Code Propane Tanks

In the 1999 addenda to the 1998 ASME pressure vessel code, Section VIII, Div. 1 there was a change in design margin for unfired pressure vessels from 4.0 to 3.5. This has resulted in the manufacture of propane and LPG tanks with thinner walls. For example, the author has purchased some new 500 gallon ASME code propane tanks for testing purposes. These tanks had the wall thickness reduced from 7.7 mm in 2000 to 7.1 mm in 2002 and now to 6.5 mm in 2004. These changes were partly due to the code change and partly due to other factors such as steel plate availability. In any case, the changes in wall thickness significantly affects the fire survivability of these tanks. This paper presents both experimental and computational results that show the effect of wall thickness on tank survivability to fire impingement. The results show that for the same dank diameter, tank material, and pressure relief valve setting, the thinner wall tanks are more likely to fail in a given fire situation. In severe fires, the thinner walled tanks will fail earlier. An earlier failure usually means the tank will fail with a higher fill level, because the pressure relief system has had less time to vent material from the tank. A higher liquid fill level at failure also means more energy is in the tank and this means the failure will be more violent. The worst failure scenario is known as a boiling liquid expanding vapor explosion and this mode of failure is also more likely with the thinner walled tanks. The results of this work suggest that certain applications of pressure vessels such as propane transport and storage may require higher design margins than required by Section VIII ASME code.

Brand and Size Matter When Choosing a Syringe to Relieve Pressure in a Tracheal Tube Cuff

We studied the use of an inline syringe as a pressure relief valve for tracheal tube cuffs during exposure to nitrous oxide to see if the technique works. Bench testing was done to determine the stick and slip characteristics of syringes of different brands and sizes. Cuffs were inflated with 20 mL of air, producing a cuff pressure of 100-120 mm Hg. Then the plunger of the syringe was allowed to passively rebound to a steady pressure at which the plunger stopped ("stick pressure"). After several minutes, pressure in the syringe was forcibly increased with a second syringe until the plunger started moving again ("slip pressure"). Stick pressure varied from 18 to 82 mm Hg depending on the brand and size of syringe used. Slip pressures exceeded stick pressures by 20-120 mm Hg. Cuff pressure increased in a linear fashion during nitrous oxide exposure, and no syringe demonstrated automatic pressure reduction. We conclude that a syringe attached to the pilot balloon connector can be used to control tracheal tube cuff pressure during nitrous oxide anesthesia. However, not all syringes are suitable for this purpose: large syringes are better than small syringes, and the Terumo brand is more suitable than BD or Monoject. The system does not work automatically, and intermittent compression of the syringe plunger to overcome static friction is required to avoid overdistension.

Dynamic analysis of proportional solenoid controlled piloted relief valve by bondgraph

In this article dynamics of a proportional controlled piloted relief valve have been studied through Bondgraph simulation technique. The governing equations of the system have been derived from the model. While solving the system equations numerically, various pressure-flow characteristics across the valve ports and the orifices are taken into consideration. The simulation study identifies some critical parameters, which have significant effect on the transient response of the system. The simulation results are also verified with experimental results. [The static and dynamic characteristics of a pressure relief valve with a proportional solenoid-controlled pilot stage, IMechE, Part I, Journal of Systems and Control Engineering, 216 (2002) 143–156.]

Nuclear equipment parts classification: a functional modeling approach

Nuclear power plants comprise a large number of components designated as safety-related. These safety-related components are subject to a special quality assurance program to assure their availability when needed, and as a result, substantiation of the product quality and suitability of these items incurs considerable costs to utilities. Furthermore, the number of vendors capable of or willing to meet nuclear-unique requirements has dwindled, forcing utilities to procure commercial grade items and dedicate them for safety-related use. Functional classification of parts, sometimes called part classification, seeks to identify the particular subset of parts associated with a safety-related component that is not relied upon for the parent component to accomplish its safety-related functions. This paper presents a functional modeling approach to part classification which is based on Goal Tree Success Tree and Master Logic Diagram (GTST-MLD). A case study for a pressure relief valve installed in an emergency diesel generator shows that the GTST-MLD provides a functional decomposition framework within which the various functions of the component can be modeled in a transparent, systematic and logical fashion in connection with a hierarchical topology of the structural elements.

Fire exposure of liquid‐filled vessels

AbstractPressure vessels in the chemical industry generally have top‐mounted pressure relief valves (PRVs) sized to handle fire exposure and other possible scenarios. Designers usually assume that the fire scenario causes liquid to boil and vapor to vent, regardless of the initial liquid level. Under some circumstances, however, a high liquid level, together with thermal expansion, can result in a vessel being full of liquid when the PRV opens. If so, the initial fluid discharged through the PRV would be a two‐phase gas‐liquid stream.This paper analyzes non‐reactive phenomena occurring during the heat‐up and venting process in non‐agitated liquid‐filled pressure vessels. A new criterion is developed to determine if the vapor‐venting sizing assumption is justified. Results from several cases show that pressures in most liquid‐filled vessels sized for vapor‐only flow will be below the ASME Code‐allowable values during fire exposure. Hence, the common industry practice of ignoring two‐phase flow when sizing fire cases is usually justified.

Hydraulic Bridge for Pressure Control in a P-Q Multiple Line Segment Control Valve

AbstractThe conventional device for flow rate and pressure multiple control is a combination of a flow rate valve and a pressure relief valve. For the pressure control, a hydraulic bridge can also be used instead of using a pressure relief valve. In this paper, a special hydraulic bridge was developed to undertake pressure control in a pressure compensated flow rate valve and thus a new type of P-Q control valve is constructed. The pressure control in this P-Q control valve is a hydraulic bridge formed by the serial connection between a metering orifice and a drain orifice. The contour of the valve port has a significant effect on the linearity of the output pressure. Theoretical analysis shows that the linear pressure output characteristic corresponds to a valve port contour of a hyperbolic. Due to the difficult machining of this hyperbolic contour, a multiple line with two segment lines is used to approximate the valve port contour for linear pressure output. The pressure bridge is constructed in a 2D P...

Expiratory Muscle Training Increases Pressure Support in High School Band Students

An experiment to increase expiratory muscle strength for instrumentalists, using a high-intensity, low-repetition expiratory training method, was conducted with 40 healthy high school band players. Subjects trained five days per week for 2 weeks using four sets of six training breaths for a total of 24 training breaths with a spring-loaded pressure relief valve that provided an adjustable threshold. The training valve pressure was set at 75% of the subject's measured maximum expiratory pressure (up to 80 cm H 2O). Results demonstrated that high-intensity, low-repetition expiratory exercises significantly increased expiratory pressure generating capacity in these subjects and the degree of the training effect was similar regardless of the instrument the band member played. The training effect occurred within 2 weeks of initiating expiratory muscle training. Thus, this simple method of expiratory-specific strength training is effective and efficient for increasing expiratory pressure support in high school band students and has possibilities of a respiratory support device for many high pressure generating purposes. The potential mechanisms of the training effect are discussed.

Fire tests to study the effect of pressure relief valve blowdown on the survivability of propane tanks in fires

AbstractThere is a significant variation in the blowdown behavior of the pressure relief valves (PRV) commonly supplied on certain commercial propane tanks. Determining how different pressure relief valve characteristics affect the survivability of a propane tank in a fire and the associated hazards, was the goal of these tests.To determine the effect of PRV blowdown, six 1890 L (500 gallon) propane tanks were exposed to an array of torch fires and thermally ruptured. A computer controlled valve was used to simulate the desired characteristics of a commercial PRV. In all cases the simulated PRV was set to open at 1.9 MPag, and blowdown was varied from 5% to 45%.The impact of the blowdown was determined by observing the nature of the failure, the time to failure, and the energy stored in the liquid and vapor phases at failure. Blast, radiation, and projectile hazards were also observed and recorded in order to determine the impact blowdown has on these pressure vessel failure hazards.An important finding of this testing is that the blowdown setting does impact the tank's survivability. It was consistently observed that large blowdown resulted in delayed failure. As a result, the PRV was open for a longer time, with a resulting reduction in hazards because of the lower fill at failure. This is believed to happen because of the lower average stress state in the tank with increased blowdown.

Modelling and dynamics of single-stage pressure relief valve with directional damping

The dynamics of a direct operated relief valve with directional damping have been studied through Bondgraph simulation technique. The governing equations of the system have been derived from the Bondgraph model. While solving the system equations numerically, the pressure-flow characteristics of the valve port and the damper unit have been taken into consideration. From this study, some significant parameters of the valve response are identified, which can be modified to improve the dynamic characteristics of the valve.