Pressure Relief Valve Research Articles

Control of an electromechanical hydrocephalus shunt--a new approach.

Hydrocephalus is characterized by an excessive accumulation of cerebrospinal fluid (CSF). Therapeutically, an artificial pressure relief valve (so-called shunt) is implanted which opens in case of increased intracranial pressure (ICP) and drains CSF into another body compartment. Today, available shunts are of a mechanical nature and drainage depends on the pressure drop across the shunt. According to the latest data, craniospinal compliance is considered to be even more important than mean ICP alone. In addition, ICP is not constant but varies due to several influences. In fact, heartbeat-related ICP waveform patterns depend on volume changes in the cranial vessels during a heartbeat and changes its shape as a function of craniospinal compliance. In this paper, we present an electromechanical shunt approach, which changes the CSF drainage as a function of the current ICP waveform. A series of 12 infusion tests in patients were analyzed and revealed a trend between the compliance and specific features of the ICP waveform. For waveform analysis of patient data, an existing signal processing algorithm was improved (using a Moore machine) and was implemented on a low-power microcontroller within the electromechanical shunt. In a test rig, the ICP waveforms were replicated and the decisions of the ICP analysis algorithm were verified. The proposed control algorithm consists of a cascaded integral controller which determines the target ICP from the measured waveform, and a faster inner-loop integral controller that keeps ICP close to the target pressure. Feedforward control using measurement data of the patient's position was implemented to compensate for changes in hydrostatic pressure during change in position. A model-based design procedure was used to lay out controller parameters in a simple model of the cerebrospinal system. Successful simulation results have been obtained with this new approach by keeping ICP within the target range for a healthy waveform.

Design and Analysis of Pressure Safety Release Valve by using Finite Element Analysis

Safety systems are installed in various industries to prevent undesirable events and to minimize the adverse effects of such events if they occur. Because of their nature, safety systems must be highly reliable. From a safety point of view, it should operate accurate at set pressure. For economic reasons, it is better to replace the safety valve devices than the total safety valve and pressure operating devices. Generally, there are different methods which are used to attain high system reliability. The majority of oil and refined-product pipelines, vessel etc. have their protection system designs based on spring- type pressure relief valves. Thus, the proper design and operation of these valves is essential to ensure the safety of operations. In simple terms, these valves have a plates which is pressed by a spring against the inlet pressure of the pipes, vessels etc.& hold these plate with help of clip ON. This arrangement helps, in quick response to release the exceed pressure inside the vessel. In these case plate is subjected to two forces, at one side a spring force & at other side is vessel pressure force. When the pressure rises in the vessel, the force generated on that side is increases and at opposite side of plate the force exerted by the spring is already present, causing, the plate to rise & break the ''clip on'' which is provided at back side of the plate and overpressure generated inside the pressure equipment is relief through the nozzle, so, line reducing the pressure level inside the equipment.

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.

The dynamic response of pressure relief valves in vapor or gas service. Part II: Experimental investigation

An experimental testing program designed to evaluate the opening stability characteristics of direct acting pressure relief valves (PRV) in gas/vapor service is described. Three different valve sizes from each of three different manufacturers were tested at two different set pressures to determine their opening characteristics (disk lift vs. time). The valves were tested with several different lengths of inlet piping as well as with and without discharge piping to determine the conditions under which unstable operation (chatter) would occur. Part I of this program described a mathematical model for predicting the dynamic response of PRV's, and the data described in this test program were used to evaluate the accuracy of the model, as described in Part III of this study to follow.

The dynamic response of pressure relief valves in vapor or gas service. Part III: Model validation

Part I of this series described a mathematical model for predicting the dynamic response and stability characteristics of a pressure relief valve in gas/vapor service, and Part II described an experimental investigation to obtain dynamic response data for various valve sizes from various manufacturers to identify conditions under which instability (chatter) could occur. This paper presents the results of the program, and shows a comparison of the model predictions with the measured dynamic response data, and discusses the information required to implement the model.

Safety instrumented systems in lieu of pressure relief valves

There are two aspects to risk assessments: safety issues and regulatory issues. Usually the two are aligned, but not always. This article explains ASME B&PVC Section VIII (Sec VIII) [American Society of Mechanical Engineers, 2013 ASME Boiler & Pressure Vessel Code: Section VIII, Division I. s.l.] requirements along with other industry guidance for using Safety Instrumented Systems (SIS) in lieu of pressure relief devices (e.g., pressure relief valves or rupture disks). For most pressure vessels in petrochemical installations in the United States, the Sec VIII requirements are regulatory requirements. A designer that is implementing facility changes from a corporate risk assessment (e.g., Layer of Protection Analysis or Hazard and Operability Study (HAZOP)) would do well to also meet the minimum regulatory requirements for overpressure in Sec VIII. Typical risk assessments allow the designer to consider both the likelihood and consequences of an overpressure scenario in determining if additional mitigation is required. Whereas, Sec VIII does not allow any credible overpressure scenarios (solely based on likelihood) unless there is adequate capacity provided by a relief device. This article discusses the detailed typical risk analysis compared to the requirements of Sec VIII overpressure protection by system design. The SIS reliability rating or determination of said rating (e.g., SIL‐3 Systems) is outside the scope of this article. © 2014 American Institute of Chemical Engineers Process Saf Prog 33: 345–349, 2014

Statististical Performance Evaluation of Soft Seat Pressure Relief Valves

Risk-based inspection methods enable estimation of the probability of failure on demand (PFD) for spring-operated pressure relief valves at the United States Department of Energy's Savannah River Site in Aiken, South Carolina. This paper presents a statistical performance evaluation of soft seat elastomer spring operated pressure relief valves. These pressure relief valves are typically smaller and of lower cost than hard seat (metal to metal) pressure relief valves. They can provide substantial cost savings in certain fluid service applications providing that PFD is at least as good as that for hard seat valves. PFD is the probability that a pressure relief valve fails to perform its intended safety function during a potentially dangerous over pressurization. The research in this paper shows that the proportion of soft seat spring operated pressure relief valves failing is the same or less than that of hard seat valves, and that for failed valves, soft seat valves typically have failure ratios of proof test pressure to set pressure much less than that of hard seat valves.

원자력 증기용 안전밸브의 개방성능 평가를 위한 해석적 연구

The purpose of this paper is to investigate an analytical approach for opening performance evaluation of the nuclear pressure safety valve based on standard codes such as ASME or KEPIC. It is well-known that safety valve is considered as one of pressure relief valves for protecting a boiler or pressure vessel from exceeding the maximum allowable working pressure. When pressure in a container reaches its set pressure, the safety valve commences discharging the internal fluid by a sudden opening called as popping. Safety valve is usually evaluated by set pressure, full open, blow-down, leakage and flow capacity. The test procedure and technical requirement for performance evaluation is described in international code of ASME code such as BPVC. The opening characteristics of steam safety valve can be analyzed by computational fluid dynamics (CFD) and steam shaft dynamics. First, the flow analysis along opening process is simulated by running the CFD models of the ten types of opening steps from 0 to 100%. As a analysis result, the various CFD outputs of flow pattern, pressure, forces on the disc and mass flow at each simulation step is demonstrated. The lift force is calculated by using the forces applied on disc from static pressure and secondary flow. And, the effect of huddle chamber or control chamber is studied by dynamic analysis based on CFD simulation results such as lift force. As a result, dynamics analysis shows opening features according to the sizes of control chamber.

Study on pressure relief system design for high temperature gas cooled reactor

Under some postulated accidental conditions, the secondary loop of the reactor needs to release its pressure for consequent system action. During the pressure relief transient, the residual fluid mixture of water and the steam will pass through the heat-exchange tubes of the steam generator and the live-steam pipeline, which decreases the steam generator pressure and the steam generator temperature due to taking the heat stored in the components away. The pressure and the temperature during the transient needs to be controlled to protect the steam generator from the potential damage. A 250 MWth high temperature gas cooled reactor is selected to evaluate this countermeasure effect during the pressure relief transient in this paper. A thermal-hydraulic system analysis code is used for modeling and simulating the pressure relief transient after the accident occurs. The temperature change of the fluid and the components in the steam generator are relative to the pressure relief transient, which is dominated by the design of pressure relief valve. Larger diameter of pressure relief valve will result in more intensive blown-down transient which causes faster pressure decrease and stronger heat transfer between the inside walls of the components in the secondary loop and the fluid. The designed pressure value where the pressure relief valve closes will affect the transient also. The designed pressure value dominates the time of the pressure relief transient which affects the amount of the fluid from the pressure relief valve. Different amount of the fluid will take away different quantity of heat from the components in the secondary loop of reactor. The pressure relief transients with a series of different diameter of pressure relief valve under some typical designed pressure value were simulated and compared. The results indicate that the pressure and the temperature of the steam generator during the pressure relief transient could be controlled effectively with reasonable design on the pressure relief system, which will provide protection and benefit for the steam generator after the postulated accident.

Design and analysis of a compact solar-driven constant-torque reaction steam turbine

The design and performance analysis of a self-sustaining, solar-driven reaction steam turbine are presented. The reaction turbine, placed horizontally, consists of two concentric cylinders with the outer one rotating with respect to the stationery inner cylinder, providing a compact and agile design. The inner cylinder, constantly filled and replenished with water, hosts conically shaped holes to allow a constant stream of feed water into the clearance between the two cylinders. With means of the thermal energy provided by the solar collector, water in the clearance will produce superheated steam that will be released in the form of steam jets causing rotational velocity, through a set of pressure relief valves placed at the surface of the outer cylinder. The main advantage of this turbine unit is the production of constant torque that is independent of temperature, with an efficiency of around 3.7%.

Design and Development of Solar Thermal Injera Baking: Steam Based Direct Baking

Ethiopia, the second most populated country in Africa, meets 96% of its energy need from bio-mass and majority of this energy goes entirely to Injera baking. Injera, a pan-cake like bread that is consumed by most of the population, demands a temperature of 180-220 oC to be well baked. Both traditional and newly developed biomass Injera stoves are energy inefficient; besides the kitchen environment is highly polluted with soot and smoke that affect the health of household inhabitants. This article introduces new technology that enables Injera baking using indirect solar stove. A parabolic dish with an aperture area of 2.54 m2, a well-insulated stainless steel pipe of 10mm, a coiled stainless steel heat exchanger, a pressure relief valve and three gate valves were equipped in the system and K-type thermocouples were used to record the temperature. The heat transfer process has been governed by the principle of natural circulation boiling-condensation between receiver and stove. A preset pressure relief valve is used to control the self-circulating working heat transfer fluid (steam at a temperature of 250 oC). The system was developed and tested for steam based direct baking in the same fashion as the traditional Injera stove. In this experiment, heat transport without significant loss from the receiver for baking at some distance is demonstrated. The challenge with manual tracking and direct steam based baking model indicates the performance of the technology can be improved. It can also win more acceptances if it is equipped with auto trackers and heat storage mechanism. In conclusion, unlike previous efforts, the experiment demonstrated that a high temperature indirect baking of Injera is possible.

Bifurcation Analysis of a Simplified Model of a Pressure Relief Valve Attached to a Pipe

A two-parameter bifurcation analysis is performed on a mathematical model that represents the motion of a pressure relief valve connected to a reservoir via a pipe. The system comprises a dimensionless system of five differential equations representing the valve position and velocity, the reservoir pressure, and the velocity and pressure components of a quarter-wave within the pipe. Two key dimensionless parameters represent the mass flow rate into the reservoir and the length of the pipe. It is found that there are two independent forms of Hopf bifurcation: a so-called valve-only instability, which involves the valve alone and occurs when the flow rate is too low, and a coupled acoustic resonance, which involves quarter-waves within the pipe, that occurs when the pipe is too long. Secondary bifurcations are also traced including curves of grazing bifurcations where the valve body first impacts with its seat. Using a mixture of simulation and numerical continuation, it is found that these instabilities in...

Design of a Novel Energy Efficient Hydraulic Tube Bender

Generally speaking, hydraulic control systems can be divided into two different driving concepts. The first one is the well-known valve-controlled system and the second one is the pump-controlled system. The former possesses the feature of fast dynamic response. However, the poor energy-saving performance is its major fault. On the contrary, the pump-controlled hydraulic system has the significant advantage of energy-saving which meets the current demand in modern machine design. In this paper, the simulation analysis using Matlab/Simulink and DSHplus for a newly developed energy-saving hydraulic tube bender is conducted. Instead of the conventional fixed displacement hydraulic pump, the new hydraulic tube bender utilizes an internal gear pump with AC servomotor as its driving power source. In the new energy-saving hydraulic circuit, the use of conventional pressure relief valve is no longer necessary since the demanded flow-rate and pressure output can be precisely obtained by continuously changing the speed of the AC servomotor. In addition, from the simulation results, it is shown that the energy-saving performance of load-sensing control scheme is somewhat better than that of constant pressure control scheme. Furthermore, the simulation results also show that the newly developed hydraulic tube bender can save up to 40% of energy consumption in a working cycle as compared to the conventional hydraulic tube bender.

Development of hydraulic normal loading device for single wheel test rig

A study was conducted to develop a hydraulic normal loading device for a single wheel test rig available in the Agricultural and Food Engineering Department of IIT Kharagpur. A hydraulic circuit was designed to apply additional normal load up to 2000 kg on wheel axle. The same circuit also can be used to remove 1350 kg load from the initial load. The circuit uses a fixed displacement pump, a 3-way-4 port-solenoid operated- spring centered directional control valve, a pressure relief valve and a double acting hydraulic cylinder. The normal load is sensed by a ring transducer and recorded in a data acquisition system. This device was used to study the effect of normal load on a radial-ply tire (14.9 to 28) under soft and hard soil condition. It was observed that, with hydraulic loading device the normal load on the wheel axle under dynamic condition was found to increase in the range of 1 to 5% for soft and hard bed soil surface. Key words: Static normal loads, dynamic normal load, radial-ply tire, drawbar pull, slip.

ANALYSIS OF DIFFERENT PROTECTION METHODS AGAINST WATER HAMMER ON WATER SUPPLY NETWORK (CASE STUDY-ASSIUT CITY NETWORK)

The effect of using different protection devices on water hammer phenomenon to provide an acceptable level of protection against system failure due to pipe collapse or bursting is presented. Water Hammer and Mass Oscillation (WHAMO) software is used in the analysis which uses the implicit finite difference scheme for solving the momentum and continuity equations at unsteady state case. Assiut city water supply network is used. The network is supplied from two points at pump No. 36 and pump No. 37. Flow of pipe network is studied under steady normal case, without any protection case against water hammer phenomenon, and the model under different operation cases; with a transient protection device(s) such as non-return valve, open surge tank, air chamber and pressure relief valve (PRV). The results are performed for three scenarios; the first is the normal operation of pump 36 and failure of pump 37, the second is the normal operation of pump 37 and failure of pump 36, and finally failure of pumps 36 and 37 together. The results showed that using of open surge tank or air chamber with non-return valve protects the pipe network effectively from the harm of water hammer. Also, using PRV with non-return valve protects the pipe network from extreme pressures. Although using non-return valve only doesn’t have a great effect on the maximum pressure head than the normal case, it protects the network from the more low pressures than without protection one. All protection cases safeguard the pipe network from the extremes of water hammer, but increase the water hammer wave period. Finally, the sudden shut down of the pumps 36 and 37 together has the large effect on the pressure heads than the shut down of any of them only.

Measurement of high amplitude relief valve noise during a full scale blowdown

Dynamic pressure fluctuations inside a pipe were measured downstream of a pressure relief valve during a full scale blowdown test. Nitrogen gas flowed with a maximum rate of 33.5 kg/s through a 3 in.x4 in. relief valve generating a peak dynamic pressure level greater than 650 kPa and sustained levels of over 450 kPa (peak). An accurate estimate of valve-generated noise is necessary when predicting radiated noise and acoustic induced vibration, which has been shown to cause fatigue failures at welded discontinuities in piping systems downstream of high pressure drop devices. These failures can be hazardous and costly, particularly when the process involves hydrocarbons such as natural gas. The measured level is compared to existing noise calculation techniques which appear to under-predict the generated noise.

Performance of sanitary sewer collection system odour control devices operating in diverse conditions

Controlling odours from sanitary sewer systems is challenging as a result of the expansive nature of these systems. Addition of oxidizing chemicals is often practiced as a mitigation strategy. One alternative is to remove odorous compounds in the gases vented from manholes using adsorptive media. In this study, odour control devices located at manholes were observed to determine the ability of these systems to reduce hydrogen sulphide from vented gases. The odour control devices incorporated pressure regulation to control gas flow out of manhole covers and adsorptive media to remove hydrogen sulphide in the vented gases prior to release. Pressure regulation was accomplished using a variable volume bladder and two pressure relief valves that permitted gas flow when pressures exceeded 1.3 to 2.5 cm water column. The reduction in gas flow vented from manholes was intended to extend the service life of the adsorptive media, as compared with odour control devices that do not incorporate pressure modulation. Devices were deployed at four locations and three adsorptive media were tested. Although measured collection system hydrogen sulphide concentrations varied from zero to over 1,000 ppm, the removal rates observed using odour control devices were typically above 90%. The lower removal rates observed at one of the sites (50.5 ± 36.1%) appeared related to high gas flow rates being emitted at this location. Activated carbon was used in most of the tests, although use of iron media resulted in the highest removal observed: 97.8 ± 3.6%. The expected service life of the adsorptive media contained within the odour control devices is a function of site-specific hydrogen sulphide concentrations and gas flow rates. The units used in this study were in service for more than 8 to 12 months prior to requiring media replacement.

The Adhesion Failure Mode in Stainless Steel Trim Spring-Operated Pressure Relief Valves

This paper addresses dangerous failures of stainless steel (SS) trim spring-operated pressure relief valves (SOPRV) due to a particular failure mode (SS-to-SS adhesion), which is not currently being included in SOPRV failure rates. As a result, current methods for estimating or predicting failure rates for SS trim SOPRV significantly underestimate these failure rates and, consequently, overestimate the safety provided by the SOPRV as measured by its average probability of failure on demand (PFDavg) or its corresponding safety integrity level (SIL). The paper also illustrates the critical importance of root cause analysis (RCA) of dangerous SOPRV failures in understanding the impacts of various failure modes. Over 1300 proof test results for both new and used SS trim SOPRV from the Savannah River Site (SRS) were identified. RCA was used on the failed valves to classify those failed due to SS-to-SS adhesions. Statistical analysis of the data convincingly demonstrates adhesions, previously assumed to be only an in-storage failure phenomenon, are also an in-service failure mode, which needs to be included in SOPRV failure rates. The paper discusses the factors which potentially influence the adhesion failure mode, and suggests a possible approach to including this mode in failure rate predictions. An example illustrates how current failure rate models overestimate SS trim SOPRV safety by 1 or 2 orders of magnitude.

An experimental study on the stability of a direct spring loaded poppet relief valve

This paper presents detailed experimental results on the static and dynamic behaviour of a hydraulic pressure relief valve with poppet valve body, with a special emphasis on the parameters influencing the valve instability. The first part of the paper presents the static measurements; sonic velocity in the hydraulic hose, discharge coefficient and fluid flow forces. The results are compared to the data found in the literature and a reasonable agreement was found. The second part presents dynamic measurements of valve chatter. While varying the feed flow rate, pressure and displacement time histories were recorded for a wide range of set pressure. It is shown that the spectra of both signals have similar frequency content, moreover, the frequency of chatter is fairly constant for a wide parameter range, both in terms of flow rate and set pressure. The regimes of qualitatively different motion forms (stable operation, free, impacting and chaotic oscillations) are shown in the flow rate–set pressure parameter plane.