Spring-loaded Pressure Relief Valve Research Articles

Evaluation of one-dimensional models to predict chatter in spring-loaded pressure relief valves for gas service

Literature models proposed to avoid valve instabilities in safety valves for gas service are evaluated. The phenomena occurring during the opening of the safety valve are described to introduce possible sources of instabilities. Models from the last thirty years are classified based on the hypothesis of the source, creating the classifications balance-based and pressure wave models. The experiments used by their authors to validate the models are evaluated. A sensitivity analysis of five models is conducted based on set pressure, inlet line diameter, ratio of specific heats and moving mass. The model results are also compared to experimental data with different gases and set pressures. In all cases the trends of the balance-based models do not match that of the pressure wave models. Compared to measurements with different set pressures, none of the tested models did both match the trends and predict a reliable inlet line length. Comparing against measurements with varying set pressure, the three percent rule only predicted a reliable inlet line length in 2 out of 5 cases. The predicted increasing trend according to the three percent rule did not match the measured trend of decreasing maximum permissible inlet line length. Based on phenomena like the spindle friction and lubrication not being included as model input parameter, and authors finding non-reproducible measurement setups, it is concluded that the instability of a safety valve is a rather stochastic process without considering additional parameters throughout the lifecycle of the safety valve.

Damping Effect on Instability of Pressure Relief Valve Used for Cargo Venting System

A mathematical model for predicting an unstable working condition called cycling of a pressure relief valve controlled by weight and spring is proposed. The valve is connected to a reservoir used to store liquid cargo by a long pipe. A transient, compressible and one-dimensional fluid dynamic equation in the pipe is numerically solved, with boundary conditions given by the valve and reservoir dynamics. The effect of valve moving part damping coefficient is analysed, which can be changed by adding dampers. Installing a damper may solve the cycling problem for weight-loaded and spring-loaded pressure relief valves. The damping coefficient of the installed damper should be carefully selected, especially for spring-loaded valves. Too large damping coefficient may cause overpressure in the reservoir when the valve opens and too low pressure when the valve closes. After all, installing damper is a theoretically possible way to prevent cycling occurrence when the pipe length is too long in some practical situations.

Optimization of Nonlinear Pressure-Flow Characteristics of a Spring-Loaded Pressure Relief Valve Based on Computational Fluid Dynamics Simulation

Abstract In this study, the nonlinear pressure-flow characteristics of a spring-loaded pressure relief valve (PRV), which is used in the automotive fuel supply system for pressure control is analyzed, and its characteristics are improved by means of geometrical modifications of the valve structure. Given the complexity of the coupling mechanism between the valve internal flow characteristics and spring system, a quasi-steady computational fluid dynamics (CFD) method is introduced to predict the nonlinear pressure-flow characteristic curve of the valve and the accuracy is validated by experimental data. The total hydraulic force on the valve spool and diaphragm are divided into three parts according to the loading position and the correlation between the internal flow characteristics, hydraulic force, and pressure-flow characteristics of the valve are explained by CFD analysis and visualization. The results show that the quasi-steady CFD method can accurately predict the trends of the valve nonlinear pressure-flow characteristic curve, which is mainly determined by the hydraulic force produced in the middle chamber of the valve. When the valve opening reaches a certain value, a main vortex would be formed in the middle chamber and lead to the sudden increase of hydraulic force which causes the fluctuation of the pressure-flow characteristic curve of the valve. It is also found that the toggle point for the flow regimes seen in the valve is affected by the geometric structure of the middle chamber and the pressure-flow characteristics can be improved by the round corner size modification.

An experimentally validated multifidelity hybrid model for analyzing the pressure variation of a relief system

In a relief system, the pressure variation in the system is often caused by the operations of the pressure control elements such as the pressure relief valve and ball valve, in addition to the pressure fluctuations in the pressure resources. This pressure variation couples with the acoustics or the motion of passive pressure control elements, which may result in system malfunction. To investigate the principles of the pressure variation in a relief system including a reservoir, a pipeline and a spring-loaded pressure relief valve, a multifidelity hybrid model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the multifidelity hybrid model, the characteristics of the pressure resources are modeled using their performance curves, the compressible gas transmitted in the pipe is calculated by one-dimensional MOC, and the air flow in the valve as well as the valve motion is simulated by a two-dimensional CFD model. To validate the model, analyses are conducted with a 1:1 scale test rig and a full CFD model. The comparison of the results shows that both the multifidelity hybrid model and the full CFD model can accurately capture the pressure fluctuations in straight pipelines induced by valve closure and predict the forms of valve motion, but the calculation speed of the multifidelity hybrid model is four times faster than that of the full CFD model.

Numerical Simulation and Analysis of the dynamic Behaviours on the Spring-loaded Pressure Relief Valve

In this paper, in engineering practice, the computational fluid dynamics method was adopted to study the dynamic characteristics of the spring-loaded pressure relief valve. The effects of different parameters on the dynamic performance were investigated by CFD simulation. In the simulation, the damping coefficient has little influence on the discharge time and reseating pressure of the relief valve. With the decrease of spring stiffness, the reseating time of pressure relief valve increases, and reducing the spring stiffness can effectively reduce the reseating pressure. The reseating pressure decreases with the rise in the distance between the upper adjusting ring and the sealing face. This simulation results can provide a reference for the design and optimization of the structural parameters of the spring-loaded pressure relief valve.

Optimization of Operation Parameters for Direct Spring Loaded Pressure Relief Valve in a Pipeline System

A direct spring loaded pressure relief valve (DSLPRV) is an efficient hydraulic structure used to control a potential water hammer in pipeline systems. The optimization of a DSLPRV was explored to consider the instability issue of a valve disk and the surge control for a pipeline system. A surge analysis scheme, named the method of characteristics, was implemented into a multiple-objective genetic algorithm to determine the adjustable factors in the operation of the DSLPRV. The forward transient analysis and multi-objective optimization of adjustable factors, such as the spring constant, degree of precompression, and disk mass, showed substantial relaxation in the surge pressure and oscillation of valve disk in a hypothetical pipeline system. The results of the regression analysis of surge were compared with the optimization results to demonstrate the potential of the developed method to substantially reduce computational costs.

Optimum design of direct spring loaded pressure relief valve in water distribution system using multi-objective genetic algorithm

Optimum design of direct spring loaded pressure relief valve in water distribution system using multi-objective genetic algorithm

Dynamic behaviour of direct spring loaded pressure relief valves connected to inlet piping: IV review and recommendations

Recent progress by a number of different groups and authors is reviewed on the stability properties of direct-spring pressure relief valves connected to pressure vessels with or without piping systems. Various different notions of stability and mechanisms for instability are revealed both in the case of gas and liquid service. It is stressed that it is not the valve itself that is stable or unstable, rather the harmful vibrations arise through interactions between the valve and its surroundings — the inlet piping, the reservoir, and any outlet piping. A distinction is drawn between underlying instability mechanisms and how these may be triggered during transient operations. The purpose of the work is to provide a coherent simplified account that will be of practical use for proposing new operational guidelines and mitigation strategies. Among these various mechanisms, oscillatory instability due to the interaction with a quarter-wave acoustic mode in the inlet piping is argued to be the most important to mitigate.

Experiments and transient simulation on spring-loaded pressure relief valve under high temperature and high pressure steam conditions

Reliable performances of high temperature and high pressure operating steam pressure relief valves (HTHP PRVs) are extremely important for the safety of nuclear power plants. It is still a challenge to accurately describe the dynamic performance of HTHP PRVs. In this study, the accuracy of computational fluid dynamics (CFD) based modelling of the transient processes is examined. For one of the HTHP PRVs named DWPRV, the effects of different parameters on the dynamic performance were investigated by combining CFD simulation and experiments. In the simulation, the domain decomposition method (DDM) and the Grid Pre-deformation Method (GPM) were adopted to handle the moving disk geometry and the large mesh deformation. The effect of damping was also studied. It is confirmed that the use of CFD simulation can improve the design and settings of a HTHP PRV in a highly energetic service that is difficult to test due to safety reasons. For the DWPRV, it was found that the maximum flow rate occurs when the curtain area is 1.18 times the throat area. The degree of superheat ranging from 0 °C to 100 °C has a negligible effect on the performance of DWPRV regardless of the changes in the material mechanical properties with operating temperatures. The reseating pressure increases linearly with the rise in the distance between the upper adjusting ring and the sealing face. The lower adjusting ring exhibits a weak effect on the reseating pressure. For the ratios of rated lift to throat diameter equaling to 0.3 and 0.35, the DWPRV exhibits the higher blowdown for the ratio of 0.35.

Dynamic behaviour of direct spring loaded pressure relief valves: III valves in liquid service

Previous studies into direct-spring pressure relief valves connected to a tank via a straight pipe are adapted to take account of liquid sonic velocity. Good agreement is found between new experimental data and simulations of a coupled fluid-structure mathematical model. Upon increasing feed mass flow rate, there is a critical pipe length above which a quarter-wave instability occurs. The dependency is shown to be well approximated by a simple analytical formula derived from a reduced-order model. Liquid service valves are found to be stable for longer inlet pipes than for the gas case. However, the instabilities when they do occur are more violent and the valve is found to jump straight into chatter, in which it impacts repeatedly with its seat. Flutter-type oscillations are never observed. These observations are explained by finding that the quarter-wave Hopf bifurcation is subcritical. Water hammer effects can also be observed, which result in excessive overpressure values during chatter. In addition a new, Helmholtz-like instability — not encountered in gas service — is identified for short pipes with small reservoir volumes. This can also be predicted analytically and is shown to explain a valve-only instability found in previous work that incorporated significant mechanical damping.

Dynamic behaviour of direct spring loaded pressure relief valves in gas service: II reduced order modelling

A previous study of gas-service direct-spring pressure relief valves connected to a tank via a straight pipe is continued by deriving a reduced-order model for predicting oscillatory instabilities such as valve flutter and chatter. The reduction process uses collocation to take into account a finite number N of acoustic pressure waves within the pipe, resulting in a set of 2N+3 ordinary differential equations. Following a novel non-dimensionalization, it is shown analytically that the model can exhibit, at experimentally realistic parameter values, instabilities associated with coupling between the valve and acoustic waves in the pipe. The thresholds for each instability are such that for a given flow rate, the first mode to go unstable as the inlet pipe length increases is the quarter-wave mode, then a three-quarter wave, a 5/4-wave etc. Thus the primary mode of instability should always be due to the quarter wave. In the limit of low flow rates, a simple approximate expression is found for the quarter-wave instability threshold in the form of inlet pipe length against mass flow rate. This threshold curve is found to agree well with simulation of the full model. For higher flow rates there is a need to include fluid convection, inlet pressure loss and pipe friction in order to get good agreement. The reduced model enables the dependence of the stability curve on key dimensionless physical parameters to be readily computed.

Residual Stress Distribution in Hard-Facing of Pressure Relief Valve Seat

In this study, for the hard-facing of spring-loaded pressure relief valve seats, the residual stress distributions after the tungsten inert gas welding, (TIG) postwelded heat treatment and subsequent surface turning were investigated. The heat input parameters of welding were calibrated using an infrared imaging and thermocouples. The residual stress distributions were computed using three-dimensional finite element model. The neutron diffraction approach was employed to verify the finite element calculation. It is found that, the surface temperature during hard-facing welding shows a double ellipsoidal shape with the highest value of around 1570 °C. The high residual stress zones are located exactly under the welded joint except a slight deviation in the hoop direction. The magnitudes of tensile residual stresses in the three directions increase with their corresponding locations from the root of the joint into the base metal. The residual stresses in all of the three directions decrease significantly after the heat treatment. After surface turning, the residual stresses are tensile except for those close to the inner surface that are compressive in axial and radial directions.

Model reduction of a direct spring-loaded pressure relief valve with upstream pipe

A mathematical model is developed of a spring-loaded pressure relief valve connected to a reservoir of compressible fluid via a single, straight pipe. The valve is modelled using Newtonian mechanics, under assumptions that the reservoir pressure is sufficient to ensure choked flow conditions. The usual assumptions of ideal gas theory lead to a system of first-order partial differential equations for the motion, energy and momentum of the fluid in the pipe. A reduced-order model is derived using a collocation method under the assumption that the dominant pipe dynamics corresponds to a standing quarter wave. The model comprises just five non-linear ordinary differential equations, representing the position and velocity of the valve body, the pressure in the tank and the velocity and pressure amplitudes of the pipe quarter wave. Through comparison with simulations of the full model using a Lax–Wendroff method, it is shown that the reduced model is quantitatively accurate and is able to predict the onset of an oscillatory valve-chatter instability. The basic trends of this instability are shown to be robust to the inclusion of pipe friction and convective effects.

Dynamic behavior of direct spring loaded pressure relief valves in gas service: Model development, measurements and instability mechanisms

A synthesis of previous literature is used to derive a model of an in-service direct-spring pressure relief valve. The model couples low-order rigid body mechanics for the valve to one-dimensional gas dynamics within the pipe. Detailed laboratory experiments are also presented for three different commercially available values, for varying mass flow rates and length of inlet pipe. In each case, violent oscillation is found to occur beyond a critical pipe length, which may be triggered either on valve opening or closing. The test results compare favorably to the simulations using the model. In particular, the model reveals that the mechanism of instability is a Hopf bifurcation (flutter instability) involving the fundamental, quarter-wave pipe mode. Furthermore, the concept of the effective area of the valve as a function of valve lift is shown to be useful in explaining sudden jumps observed in the test data. It is argued that these instabilities are not alleviated by the 3% inlet line loss criterion that has recently been proposed as an industry standard.

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.

Zone modelling of high-lift pressure relief valves

The lift attained by automatic spring-loaded pressure relief valves depends upon spring selection and upon the variation in hydrodynamic thrust on the moving parts. Accurate prediction of the latter is difficult, requiring analysis of the complex multidimensional flow beneath the disc. A simple zonal model is suggested that enables designers to identify key geometric and dynamic parameters. Comparison is made between model predictions and published experimental data. Limitations are also considered and work to improve the general use of the model in product development is identified.