Non-return Valve Research Articles

Prolonged "phantom" square wave capnograph tracing after patient disconnection or extubation. Potential hazard associated with the Siemens Servo 900c ventilator.

The authors report on the appearance of misleading square wave "phantom" capnograph tracings for approximately 3 min after disconnection from the Siemens Servo 900c ventilator. A series of experiments are described to examine the mechanism of this phenomenon. Patients were ventilated using the Siemens Servo 900c ventilator with the following settings: minute volume, 5 1/min; respiratory rate, 8 breaths/min; PEEP, 0 cm H2O; trigger sensitivity, 20 cm H2O. The ventilator was connected to the Siemens Servo Evac 180 evacuation system (25 1/min on evacuation flowmeter). Airway pressure and capnography were recorded at the Y piece during ventilation and after disconnection. A back-up ventilator was used to support the patient during disconnection of the ventilator being studied. Initially, the "phantom" capnograph tracing closely resembled the square wave capnograph tracing before disconnection, but the amplitude and shape of the waveform gradually decayed. Based on experiments described in this article, the authors show that the carbon dioxide for the "phantom" capnograph tracing comes from the gas exhaled by the patient in the last breaths before disconnection and which is present in both the expiratory tubing and in the evacuation system. The small pressure gradient between the exhaust reservoir and the atmosphere causes reverse flow of expired gas after disconnection, when both the nonreturn flap valve at the exhaust outlet is open (due to minimal valve incompetence) and when the expiratory servo valve is open (in the absence of positive end-expiratory pressure). This continuous reverse flow is detected by the capnograph but is interrupted intermittently by each attempted positive pressure ventilation, thereby creating a "phantom" capnograph. After accidental disconnection of the patient from the breathing system, or after accidental extubation of the trachea, the "phantom" capnograph is likely to confuse even an experienced anesthesiologist into the mistaken belief that his rapidly deteriorating patient is being ventilated adequately. Several potential mechanisms to eliminate this phenomenon are outlined, including the avoidance of zero positive end-expiratory pressure. "Phantom" capnography provides an illustration of the dangers of using monitoring techniques, however reliable, as a substitute for vigilant clinical observation.

WATERHAMMER DAMAGE OF VALVES IN A PUMPING STATION—AN INVESTIGATIVE STUDY

ABSTRACT Four incident cases of sluice valve cap and body bursts were reported for a pumping station of water works. Waterhammer analyses were carried out for all incident cases by modelling the observed conditions. Special emphasis was given to the closure of conventional non-return valve (NRV) with time-lag after flow reversal. Delayed closure of NRVs was the cause of the observed cap and body bursts of the old sluice valves under transient conditions. Though several other methods of protection including the provision of air chamber were examined, they were not suggested/recommended from cost-effective and time response points of view. Replacement of the existing conventional NRVs with non-slam and fast-acting ones solved the problem and since then the system has been working satisfactorily.

Shutdown process simulation of a refrigeration plant having a twin screw compressor

Non-return valves in refrigeration systems are sources of inefficiency due to flow pressure drop, and of unreliability due to the accumulation of flow debris. Hence the attractiveness of schemes to remove them. In twin screw compressor plants of a certain configuration the suction non-return valve was removed and a reverse rotation brake was fitted to the free end of the motor shaft to prevent backflow of the (oil-laden) refrigerant and reverse rotation of the compressor rotors immediately following plant shutdown. Brake failures occurred on site. This paper describes one part of the subsequent investigation, namely the adaptation of a program created to calculate normal running torque to the process calculating the maximum static torque to occur following shutdown. Shutdown torques up to 60% greater than the running torque are predicted but are thought to be underestimates due to the distribution of oil following shutdown being different from that during normal operation. The authors believe that, following shutdown, the oil seals the exit leakage path across the contact line but clears away from the inlet path through the blow hole allowing unexpectedly high cavity pressures and torques to develop. In existing plants fitted with brakes chosen on the assumption that the shutdown torque will be no greater than the running torque, a safe shutdown may be obtained by opening the slide valve prior to shutdown.

Development of Prototype Pump Using a Vibrating Pipe With a Valve

Tests were conducted on a prototype pump which has an extremely simple structure and excellent controllability. Its structural and hydrodynamic features are different from those of previous conventional reciprocating pumps. The pump structure constitutes a leak-proof short vibrating pipe equipped with a nonreturn valve on the edge of its outlet. The authors developed a prototype pump which uses a 25 mm diameter vibration pipe and an electromagnetic excitation device. The pump performance, intentionally changed by adjusting the coil voltage or the coil current frequency, featured a maximum pressure of approximately 1.0 bars, a maximum flow rate of approximately 40 liters per minute, and a maximum efficiency of approximately 30 percent. Results of both a one-year test run, using water as the working medium, and a three-month durability test, using concentrated nitric acid as the working fluid, assuming application as a chemical pump, indicated favorable results.

Prototype Pump Driven by Air Actuator for High-Temperature Molten Material.

Safe conveyance of high-temperature molten materials is an essential facter for some advanced industries. The authors developed a new prototype pump for such applications. The pump utilized the pumping effect of a vibrating pipe system and featured a simple and novel configuration. Its structural and hydrodynamic features are different from those of previous conventional pumps. The pump structure constitutes a short vibrating pipe with a nonreturn valve, a long connecting rod and a cylindrical casing. It was driven by an air actuator. Tests were carried out with this prototype pump using high-temperature molten salt of 473 K to 673 K as a test fluid. Test results indicated that the air actuator was suitable to drive the pump and the pump performance was stable even at such high temperatures.

5267445 Cryomagnet system with a low-loss helium cryostat of minimized disturbances

A cryomagnet system, in particular for use with nuclear magnetic resonance (NMR) experiments or ion cyclotron resonance (ICR) experiments, with a low-loss helium cryostat (1) comprising a helium container (2) and one or a plurality of tubes for the feed or exit of helium into or out of the helium container (2), respectively, the tubes being sealed to the atmosphere outside the helium container (2) by at least one non-return low-pressure valve (4), wherein at least one exhaust pipeline (3) is provided with a device for dissipating the energy of the expanding helium. Such a device may consist of a chamber which is deviated from the exhaust pipeline (3) and has a wall material of very high extensibility, e.g. a folding balloon. Yet the device may also consist of a flow baffle which is provided in the exhaust pipeline (3), for example a porous disc (6). The device withdraws kinetic energy from thermo-acoustic oscillations of the helium gas column in the conduit system of the cryostat and thus dampens the detrimental oscillations which entrain increased losses of helium and disturbance of the magnetic field at the locus of the sample (FIG. 3a).

Computer simulation of equilibrium conditions following a plant ‘trip’

When a process or part of a process experiences an emergency ‘trip’, the contained fluids redistribute themselves based upon the prevailing pressure gradients and depending upon the positions of valves at the time of the trip. Reverse flow through rotating compression machinery may occur, depending upon the locations of non-return valves. Reduction in pressure and mixing of cryogenic fluids of different compositions and/or temperatures can both lead to generation of significant volumes of vapour. This equilibration process is usually largely over in a matter of seconds rather than minutes. Key questions facing process and mechanical designers are: what is the settle-out pressure, and can we ensure relief valves do not lift following a trip? To answer these related questions it is necessary to analyse the state of the system prior to the trip, and then, based upon valve positions, etc., construct a model of the worst case probable scenarios for the qualitative redistribution of fluid inventory. At this point the simulation program may be employed to help calculate rigorously the final settle out conditions for each of the possible scenarios. This technique is particularly appropriate for cryogenic processes including refrigeration cycles. It is illustrated here with the help of a multistage hydrocarbon compressor example. Other related non-standard applications of the steady state process simulation program are identified.

Computer simulation of the hydraulic milking method

SummaryA mathematical model of the interactions within a milking machine teatcup has been developed, which describes the relationship between liner wall movement, pressures and flow rate when milking without an air inlet. It is based on equations of motion for a column of incompressible fluid and requires a second-order, non-linear differential equation to be solved. Incorporating a non-return valve allows hydraulic milking to be modelled, and the comparison between predicted and measured pressures, flow rates and liner wall movement when milking hydraulically is shown. The model can be used to optimize milking conditions to reduce vacuum peaks, improve liner opening and thus maximize flow rate.

A low-pressure portable anaesthesia system for field use: clinical trials

This is a report of our experience with a portable anaesthesia system that was developed for use under field conditions, when compressed gas supplies are limited. We first assembled and bench-tested a low-pressure plenum system, based upon the Farman entrainer. The entrainer required a low flow of compressed gas, O2 at 1-2 L.min-1, and generated a low-pressure mixture of O2 and air which was directed through an Oxford miniature vaporizer, a non-return valve, and a widebore T-piece circuit. With this system we anaesthetized 24 patients with intermittent positive pressure ventilation (IPPV) and nine patients breathing spontaneously. During IPPV, the circuit resembled a T-piece and provided effective gas exchange with a FGF of 1.2 times minute ventilation. Inspiratory and expiratory valves were arranged so that the spontaneous mode was non-rebreathing, and FGF was adjusted to equal minute ventilation. The system was very economical, using 1-2 L.min-1 O2 and 20-25 ml.hr-1 liquid halothane to produce a FGF of 6-10 L.min-1, an FIO2 of 0.33, and FIhal of 1-1.5 per cent. We have demonstrated that this is a versatile, safe, and economical system, compatible with the practice of modern inhalational anaesthesia under field conditions. It can be readily assembled from commercially available components.

Improved milking characteristics of teatcups fitted with non-return valves

SummaryThe milking characteristics of conventional clusters were compared with individual teatcups or clusters fitted with valves in the short milk tubes without external air admission to the liners. Individual teatcups fitted with non-return valves had peak milk flow rates 13% higher than conventional teatcups. A daily cross-over experiment involving 36 cows compared clusters fitted with non-return valves to conventional clusters. Valved clusters milked 18% faster, showed significantly better teatcup stability and 3% higher machine milk yields, but 48% higher strip yields were recorded. Clusters with non-return valves were difficult to remove after milking because the valve closed when the vacuum supply was shut off, thereby maintaining the vacuum level under the teats. When the nominal plant vacuum level for teatcups with non-return valves was reduced by 10 kPa to compensate for the higher effective milking vacuum level, the valved teatcups had peak flow rates 20% lower than the conventional teatcups. Clusters fitted with a modified valve, which allowed some reverse flow when closed (a ‘leaky’ valve), milked significantly faster than conventional clusters, had 33% lower strip yields and were easy to remove after milking.

Increased milking vacuum in teatcups fitted with non-return valves

SummaryAn experimental non-return valve was fitted in the short milk tube so that flow was permitted only in one direction, away from the teat. Liner movement was minimal because no air admission to the liner above the valve was provided. The extent of liner opening therefore depended on the amount of milk extracted within a pulsation cycle and on any air leakage past the liner mouthpiece. Milking experiments using four cows showed that the mean vacuum level in nominally open liners of valved teatcups during peak milk flow was 8·6 kPa higher than in conventional teatcups. Bench tests showed that the increase in liner vacuum (LV) depended on the nominal plant vacuum level, the pressure difference between initial LV and maximum pulsation chamber vacuum, the liner elasticity and mounting tension. The main source of energy available to raise LV above the nominal plant vacuum is the release of strain energy, stored within the liner during the collapse phase of each pulsation cycle.

Aerodynamic characteristics of models of nonreturn devices and valves for main gas pipelines

Aerodynamic characteristics of models of nonreturn devices and valves for main gas pipelines

A digital simulation method of the pressure pulsations in reciprocating compressor-piping systems. 1st report Calculation method.

One method of analyzing pressure pulsations is to use an analog simulation which can consider the interaction between a compressor and the attached piping. Conventional digital pulsation analyses, in which suction/discharge gas flow is one-sidedly applied as a forcing function, do not consider the interaction effects. This paper describes new digital simulation methods which can account for a compressor-piping interaction. In these methods, non-return valves and the stroke of the valves of compressors are expressed by nonlinear damping and nonlinear stiffness respectively. The dynamic equation of the total system is constructed by assembling the characteristic equations of each element using the finite element method. This governing equation is integrated time historically using the Newmark-β method ; and then the flow rate and pressure variation are obtained. By using the above methods, the following three types of digital simulations were carried out for a compressor-piping model : (1) conventional digital simulation (2) new digital simulation equivalent to the analog simulation (3) new digital simulation including the valve dynamics. From these calculations, it is demonstrated that this present method has the same capability as the analog simulation. Furthermore, it is shown that this new method can deal with more detailed interactions by considering the valve dynamics, which is difficult to account for in the analog simulation.

Disturbed Sampling Using Reverse Circulation

Abstract The exploration of unconsolidated and semi-consolidated strata is generally undertaken using shell and auger and continuous flight augering techniques. These methods have serious limitations, especially when accurate sampling is required below the water table. To improve the reliability of samples British Industrial Sand Ltd. have developed a drill bit for use with reverse circulation drilling. When used in combination with a non-return valve this method allows continuous drilling and sampling both above and below the water table. Comparisons with other drilling techniques show that the duo-pipe method is capable of delivering uncontaminated samples and recovering material of all anticipated size ranges. The system could be adapted for use in the exploration of other mineral deposits e.g. alluvial tin, beach sands, sand and gravel, or for offshore drilling programmes.

Does data on reliability tell us about equipment or people?

Many failures, particularly of mechanical equipment, are due, not to inherent weaknesses in the equipment but to poor installation or maintenance or to misuse. The failure rate can thus vary greatly between one organisation and another and tells us little about the equipment, more about the people who maintain and operate it. Examples considered include bellows, pipelines, machinery, non-return valves and furnaces. The failure data may still be useful as a guide to action; it may show which equipment cannot withstand poor installation, maintenance or operation and is therefore best avoided when possible or it may indicate a need for better training or auditing. In some cases suppliers should provide more information on installation or maintenance procedures or conditions of use.

Causes And Control Of Water Hammer

Water hammer, or surge, is defined as the momentary increase in flow or pressure that passes lengthwise along a conduit. This article discusses the causes and effects of water hammer, methods of control, and the problem of air in pipelines and how to combat it. Methods of controlling water hammer include: controlled valves; flywheel or pump motor; standpipe; air vessel or surge tank; one‐way surge tank; reservoir of water; suction pipe; surge relief valve; nonreturn valve; and reversal of pump.

SOURCES OF ERROR AND THEIR CORRECTION IN THE MEASUREMENT OF CARBON DIOXIDE ELIMINATION USING THE SIEMENS-ELEMA CO2 ANALYZER

The Siemens-Elema CO2 Analyzer 930 allows calculation of carbon dioxide elimination from the instantaneous measurement of expired gas flow (VE) and carbon dioxide fraction (FECO2). VE is measured in the ventilator and FECO2 at the Y-piece. The most important source of error in the measurement of carbon dioxide elimination is rebreathing, which corresponds to about 24 ml of end-expiratory gas per breath with the standard Y-piece and tubing. This problem may be decreased by the use of non-return valves in the Y-piece. Allowance must be made for the effects of intermolecular interaction between carbon dioxide and the carrier gas, as the reading is about 20% greater with nitrous oxide than with oxygen. This problem can be largely circumvented by calibration with appropriate gas mixtures. Errors resulting from analyser delay are small, and are eliminated completely by the inclusion of fast electronic components. Carbon dioxide analysis is linear with air as carrier gas, but slightly alinear with nitrous oxide in oxygen mixtures. This error can be minimized by using calibration gases with a carbon dioxide content close to that of expired gas. The expiratory flow meter is linear if kept in good condition. Variations in temperature and water content of expired gas cause overestimation of mean expired carbon dioxide fraction (FECO2) by a factor of 1.01-1.02. Compressed gas in the tubing causes a small error which may be neglected at normal airway pressures with tubing of low compliance. Carbon dioxide measurement is slightly affected by barometric pressure. During mechanical ventilation of the lungs in 10 patients with air, FECO2 obtained after corrections for known errors agreed well with Scholander analysis of mixed expired gas.

Achieving thermal rectification in natural-circulation solar-energy water heaters

Thermal rectification is often required in solar-energy water heating systems in order to prevent unwanted heat leaks which occur at night as a result of reverse thermosyphonic motions from the store to the solar-energy collector. Conventional methods of accomplishing such a thermal rectification are reviewed, and novel non-return valves for this purpose and their potential applications are described.

Nonreturn valves in occlusion pumps in heart and lung machines

1. Tests have been performed on roller-type occlusion pumps with and without nonreturn valves at the output from the pump and have shown that it is possible to reduce the magnitude of the fluctuations in the heart and lung machine and to increase the flow by eliminating into the elastic chamber.

A MODEL FOR CALCULATING STEADY-STATE FLOW IN A WATER NETWORK

Calculation of steady-state pressure and flow distributions in a water network is an important requirement for network operators and planners. The SWAN model described in this report is suitable for simulation of networks comprising pipes, non-return and pressure-reducing valves, pumps and storage tanks or reservoirs. Mathematical formulation of the model is based on description of its hydraulic elements by algebraic equations and nodal topological network analysis procedure. The non-linear model equations are solved by application of the NEWTON-RAPHSON method. Used in conjunction with sparse matrix triangularization and convergence acceleration procedures, this method can be used to calculate large networks, whilst maintaining calculation times and the amount of data storage within reasonable limits. An application of the SWAN model to test and real networks is presented as an example.