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120-495: The air handling function of a PLSS is similar to that of a diving rebreather , in that exhaled gases are recycled into the breathing gas in a closed loop. When used in a microgravity environment, a separate propulsion system is generally needed for safety and control, since there is no physical connection to a spacecraft. The portable life support system used in the Apollo lunar landing missions used lithium hydroxide to remove

240-401: A fire hydrant . The meters are normally made of aluminum to be lightweight, and are usually 7.5 cm (3 in) capacity. Water utilities often require them for measurement of water used in construction, pool filling, or where a permanent meter is not yet installed. The Woltman meter (invented by Reinhard Woltman in the 19th century) comprises a rotor with helical blades inserted axially in

360-459: A 279 watt-hour battery. For the extended missions of Apollo 15 through 17, the EVA stay time was doubled to 8 hours by increasing oxygen to 1,430 pounds per square inch (9.9 MPa), lithium hydroxide to 3.12 pounds (1.42 kg), cooling water to 11.5 pounds (5.2 liters), and battery capacity to 390 watt-hours. An emergency backup was provided in case the main system failed, by a separate unit called

480-750: A conditioning device as well as a differential pressure producer. Upstream requirements are between 0–5 diameters compared to up to 44 diameters for an orifice plate or 22 diameters for a Venturi. Because cone meters are generally of welded construction, it is recommended they are always calibrated prior to service. Inevitably heat effects of welding cause distortions and other effects that prevent tabular data on discharge coefficients with respect to line size, beta ratio and operating Reynolds numbers from being collected and published. Calibrated cone meters have an uncertainty up to ±0.5%. Un-calibrated cone meters have an uncertainty of ±5.0% Linear resistance meters, also called laminar flowmeters, measure very low flows at which

600-550: A fire hazard, so the more successful applications have been for space-suits, fire-fighting and mine rescue. A liquid oxygen supply can be used for oxygen or mixed gas rebreathers. If used underwater, the liquid-oxygen container must be well insulated against heat transfer from the water. Industrial sets of this type may not be suitable for diving, and diving sets of this type may not be suitable for use out of water due to conflicting heat transfer requirements. The set's liquid oxygen tank must be filled immediately before use. Examples of

720-512: A helical screw. Because they are used for domestic water measurement, piston meters, also known as rotary piston or semi-positive displacement meters, are the most common flow measurement devices in the UK and are used for almost all meter sizes up to and including 40 mm ( 1 + 1 ⁄ 2  in). The piston meter operates on the principle of a piston rotating within a chamber of known volume. For each rotation, an amount of water passes through

840-424: A highly repeatable measurement over the life of the product. Because distance between the two laser sheets does not change, optical flowmeters do not require periodic calibration after their initial commissioning. Optical flowmeters require only one installation point, instead of the two installation points typically required by other types of meters. A single installation point is simpler, requires less maintenance and

960-459: A large penstock such as used at a hydroelectric power plant can be measured by averaging the flow velocity over the entire area. Propeller-type current meters (similar to the purely mechanical Ekman current meter , but now with electronic data acquisition) can be traversed over the area of the penstock and velocities averaged to calculate total flow. This may be on the order of hundreds of cubic meters per second. The flow must be kept steady during

1080-417: A large range of options are available depending on the specific application and available budget. A diving rebreather is safety-critical life-support equipment – some modes of failure can kill the diver without warning, others can require immediate appropriate response for survival. A helium reclaim system (or push-pull system) is used to recover helium based breathing gas after use by the diver when this

1200-402: A long porous plug; such low flows create small pressure differentials but longer flow elements create higher, more easily measured differentials. These flowmeters are particularly sensitive to temperature changes affecting the fluid viscosity and the diameter of the flow element, as can be seen in the governing Hagen–Poiseuille equation . A "variable area meter" measures fluid flow by allowing

1320-404: A loop configured machine has two unidirectional valves so that only scrubbed gas flows to the patient while expired gas goes back to the machine. The anaesthetic machine can also provide gas to ventilated patients who cannot breathe on their own. A waste gas scavenging system removes any gasses from the operating room to avoid environmental contamination. One of the functions of a space suit

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1440-446: A lower pressure in the suit which gives the wearer better freedom of movement. Submarines , underwater habitats , bomb shelters, space stations , and other living spaces occupied by several people over medium to long periods on a limited gas supply, are equivalent to closed circuit rebreathers in principle, but generally rely on mechanical circulation of breathing gas through the scrubbers. Flow measurement Flow measurement

1560-405: A maximum of about 30 minutes of emergency oxygen for breathing and cooling. This could be extended to 75 to 90 minutes with a "buddy system" hose that used the other astronaut's functional PLSS for cooling (only). This allowed the vent valve to be partly closed to decrease the oxygen flow rate. The PLSS was 26 inches (66 cm) high, 18 inches (46 cm) wide, and 10 inches (25 cm) deep. It

1680-550: A naturally hypoxic environment. They need to be lightweight and to be reliable in severe cold including not getting choked with deposited frost. A high rate of system failures due to extreme cold has not been solved. Breathing pure oxygen results in an elevated partial pressure of oxygen in the blood: a climber breathing pure oxygen at the summit of Mount Everest has a greater oxygen partial pressure than breathing air at sea level. This results in being able to exert greater physical effort at altitude. The exothermic reaction helps keep

1800-464: A newer differential pressure metering device first launched in 1985 by McCrometer in Hemet, CA. The cone meter is a generic yet robust differential pressure (DP) meter that has shown to be resistant to effects of asymmetric and swirling flow. While working with the same basic principles as Venturi and orifice type DP meters, cone meters don't require the same upstream and downstream piping. The cone acts as

1920-435: A number of hoses and electrical cables twisted together and deployed as a unit. This is extended to the divers through the diver umbilicals. The accommodation life support system maintains the chamber environment within the acceptable range for health and comfort of the occupants. Temperature, humidity, breathing gas quality, sanitation systems, and equipment function are monitored and controlled. An atmospheric diving suit

2040-526: A particle crosses the first beam. The detecting optics collects scattered light on a photodetector, which then generates a pulse signal. As the same particle crosses the second beam, the detecting optics collect scattered light on a second photodetector, which converts the incoming light into a second electrical pulse. By measuring the time interval between these pulses, the gas velocity is calculated as V = D / t {\displaystyle V=D/t} where D {\displaystyle D}

2160-454: A pendulum rebreather. Breathing hoses can be tethered down to a diver's shoulders or ballasted for neutral buoyancy to minimise loads on the mouthpiece. A mouthpiece with bite-grip , an oro-nasal mask , a full-face mask , or a sealed helmet is provided so that the user can breathe from the unit hands-free. A store of oxygen, usually as compressed gas in a high pressure cylinder, but sometimes as liquid oxygen , that feeds gaseous oxygen into

2280-468: A rotary separator. The removed water is stored and used to supplement the water supply used in the LCVG. The sublimator also cools the remaining oxygen to about 55 °F (13 °C). A flow sensor monitors the flow rate. Extra oxygen is added to the flow from a storage tank as necessary, downstream of the flow sensor. The oxygen is then returned to the suit at the back of the head, where it flows down over

2400-425: A wide enough bore to minimise flow resistance at the ambient pressure in the operational range for the equipment, are usually circular in cross section, and may be corrugated to let the user's head move about without the tube collapsing at kinks. Each end has an airtight connection to the adjacent component, and they may contain a one-way valve to keep the gas circulating the right way in a loop system. Depending on

2520-409: Is a device inserted into the flowing fluid that produces a physical property that can be accurately related to flow. For example, an orifice plate produces a pressure drop that is a function of the square of the volume rate of flow through the orifice. A vortex meter primary flow element produces a series of oscillations of pressure. Generally, the physical property generated by the primary flow element

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2640-468: Is a shortened version of a Venturi meter, with a lower pressure drop than an orifice plate. As with these flowmeters the flow rate in a Dall tube is determined by measuring the pressure drop caused by restriction in the conduit. The pressure differential is typically measured using diaphragm pressure transducers with digital readout. Since these meters have significantly lower permanent pressure losses than orifice meters, Dall tubes are widely used for measuring

2760-435: Is a small one-man articulated submersible of roughly anthropomorphic form, with limb joints which allow articulation under external pressure while maintaining an internal pressure of one atmosphere. Breathing gas supply may be surface supplied by umbilical, or from a rebreather carried on the suit. An emergency gas supply rebreather may also be fitted to a suit with either surface supply or rebreather for primary breathing gas. As

2880-414: Is a variable area orifice, where a spring-loaded tapered plunger is deflected by flow through an orifice. The displacement can be related to the flow rate. Optical flowmeters use light to determine flow rate. Small particles which accompany natural and industrial gases pass through two laser beams focused a short distance apart in the flow path in a pipe by illuminating optics. Laser light is scattered when

3000-428: Is a velocity type meter which has an impeller which rotates horizontally on a vertical shaft. The impeller element is in a housing in which multiple inlet ports direct the fluid flow at the impeller causing it to rotate in a specific direction in proportion to the flow velocity. This meter works mechanically much like a single jet meter except that the ports direct the flow at the impeller equally from several points around

3120-502: Is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, while also eliminating the bubbles otherwise produced by an open circuit system. The latter advantage over other systems is useful for covert military operations by frogmen , as well as for undisturbed observation of underwater wildlife. A rebreather

3240-402: Is calcium hydroxide, which is relatively cheap and easily available. Other components may be present in the absorbent. Sodium hydroxide is added to accelerate the reaction with carbon dioxide. Other chemicals may be added to prevent unwanted decomposition products when used with standard halogenated inhalation anaesthetics. An indicator may be included to show when carbon dioxide has dissolved in

3360-460: Is designed to record instantaneous velocity components at a single point with a relatively high frequency. Measurements are performed by measuring the velocity of particles in a remote sampling volume based upon the Doppler shift effect. Thermal mass flowmeters generally use combinations of heated elements and temperature sensors to measure the difference between static and flowing heat transfer to

3480-401: Is forced out of the meter as the gear teeth mesh and reduce the available pockets to nearly zero volume. Helical gear flowmeters get their name from the shape of their gears or rotors. These rotors resemble the shape of a helix, which is a spiral-shaped structure. As the fluid flows through the meter, it enters the compartments in the rotors, causing the rotors to rotate. The length of the rotor

3600-413: Is generally understood to be a portable apparatus carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system . Rebreather technology may be used where breathing gas supply is limited, such as underwater, in space, where the environment is toxic or hypoxic (as in firefighting), mine rescue, high-altitude operations, or where

3720-420: Is important, such as in space stations and space suits. Lithium peroxide also replenishes the oxygen during the scrubbing reaction. Another method of carbon dioxide removal occasionally used in portable rebreathers is to freeze it out, which is possible in a cryogenic rebreather which uses liquid oxygen. The liquid oxygen absorbs heat from the carbon dioxide in a heat exchanger to convert the oxygen to gas, which

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3840-425: Is indicated by a gearing and register arrangement, which is connected to the disk. It is reliable for flow measurements within 1 percent. The turbine flowmeter (better described as an axial turbine) translates the mechanical action of the turbine rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The turbine tends to have all the flow traveling around it. The turbine wheel

3960-613: Is less of a problem. The Soviet IDA71 rebreather was also manufactured in a high altitude version, which was operated as an oxygen rebreather. Anaesthetic machines can be configured as rebreathers to provide oxygen and anaesthetic gases to a patient during surgery or other procedures that require sedation. An absorbent is present in the machine to remove the carbon dioxide from the loop. Both semi-closed and fully closed circuit systems may be used for anaesthetic machines, and both push-pull (pendulum) two directional flow and one directional loop systems are used. The breathing circuit of

4080-404: Is less prone to errors. Commercially available optical flowmeters are capable of measuring flow from 0.1 m/s to faster than 100 m/s (1000:1 turn down ratio) and have been demonstrated to be effective for the measurement of flare gases from oil wells and refineries, a contributor to atmospheric pollution. Open channel flow describes cases where flowing liquid has a top surface open to

4200-439: Is more convenient to measure than the flow itself. The properties of the primary flow element, and the fidelity of the practical installation to the assumptions made in calibration, are critical factors in the accuracy of the flow measurement. A positive displacement meter may be compared to a bucket and a stopwatch. The stopwatch is started when the flow starts and stopped when the bucket reaches its limit. The volume divided by

4320-427: Is more economical than losing it to the environment in open circuit systems. The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours, and pressurised into storage containers, where it may be mixed with oxygen to the required composition for re-use, either immediately, or at a later date. The life support system provides breathing gas and other services to support life for

4440-679: Is not equivalent to the same gas under different conditions. References will be made to "actual" flow rate through a meter and "standard" or "base" flow rate through a meter with units such as acm/h (actual cubic meters per hour), sm /sec (standard cubic meters per second), kscm/h (thousand standard cubic meters per hour), LFM (linear feet per minute), or MMSCFD (million standard cubic feet per day). Gas mass flow rate can be directly measured, independent of pressure and temperature effects, with ultrasonic flow meters , thermal mass flowmeters , Coriolis mass flowmeters , or mass flow controllers . For liquids, various units are used depending upon

4560-423: Is set in the path of a fluid stream. The flowing fluid impinges on the turbine blades, imparting a force to the blade surface and setting the rotor in motion. When a steady rotation speed has been reached, the speed is proportional to fluid velocity. Turbine flowmeters are used for the measurement of natural gas and liquid flow. Turbine meters are less accurate than displacement and jet meters at low flow rates, but

4680-515: Is sufficient that the inlet and outlet are always separated from each other thus blocking a free flow of liquid. The mating helical rotors create a progressive cavity which opens to admit fluid, seals itself off and then opens up to the downstream side to release the fluid. This happens in a continuous fashion and the flowrate is calculated from the speed of rotation. This is the most commonly used measurement system for measuring water supply in houses. The fluid, most commonly water, enters in one side of

4800-399: Is sufficient to freeze the carbon dioxide. This process also chills the gas, which is sometimes, but not always, desirable. A breathing hose or sometimes breathing tube on a rebreather is a flexible tube for breathing gas to pass through at ambient pressure. They are distinguished from the low-, intermediate-, and high-pressure hoses which may also be parts of rebreather apparatus. They have

4920-481: Is the Thorpe tube flowmeter . Floats are made in many different shapes, with spheres and spherical ellipses being the most common. Some are designed to spin visibly in the fluid stream to aid the user in determining whether the float is stuck or not. Rotameters are available for a wide range of liquids but are most commonly used with water or air. They can be made to reliably measure flow down to 1% accuracy. Another type

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5040-614: Is the distance between the laser beams and t {\displaystyle t} is the time interval. Laser-based optical flowmeters measure the actual speed of particles, a property which is not dependent on thermal conductivity of gases, variations in gas flow or composition of gases. The operating principle enables optical laser technology to deliver highly accurate flow data, even in challenging environments which may include high temperature, low flow rates, high pressure, high humidity, pipe vibration and acoustic noise. Optical flowmeters are very stable with no moving parts and deliver

5160-427: Is the earliest type of rebreather and was commonly used by navies for submarine escape and shallow water diving work, for mine rescue, high altitude mountaineering and flight, and in industrial applications from the early twentieth century. Oxygen rebreathers can be remarkably simple and mechanically reliable, and they were invented before open-circuit scuba. They only supply oxygen, so there is no requirement to control

5280-457: Is the flow rate, K {\displaystyle K} is a constant, H {\displaystyle H} is the water level, and X {\displaystyle X} is an exponent which varies with the device used; or it is converted according to empirically derived level/flow data points (a "flow curve"). The flow rate can then be integrated over time into volumetric flow. Level to flow devices are commonly used to measure

5400-417: Is the quantification of bulk fluid movement. Flow can be measured using devices called flowmeters in various ways. The common types of flowmeters with industrial applications are listed below: Flow measurement methods other than positive-displacement flowmeters rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring

5520-400: Is the volumetric flow rate multiplied by the energy content per unit volume or mass flow rate multiplied by the energy content per unit mass. Energy flow rate is usually derived from mass or volumetric flow rate by the use of a flow computer . In engineering contexts, the volumetric flow rate is usually given the symbol Q {\displaystyle Q} , and the mass flow rate,

5640-522: Is then available again to react with more carbonic acid. 100 grams (3.5 oz) of this absorbent can remove about 15 to 25 litres (0.53 to 0.88 cu ft) of carbon dioxide at standard atmospheric pressure. This process also heats and humidifies the air, which is desirable for diving in cold water, or climbing at high altitudes, but not for working in hot environments. Other reactions may be used in special circumstances. Lithium hydroxide and particularly lithium peroxide may be used where low mass

5760-427: Is to provide the wearer with breathing gas. This can be done via an umbilical from the life-support systems of the spacecraft or habitat, or from a primary life support system carried on the suit. Both of these systems involve rebreather technology as they both remove carbon dioxide from the breathing gas and add oxygen to compensate for oxygen used by the wearer. Space suits usually use oxygen rebreathers as this allows

5880-421: Is usually necessary to eliminate the metabolic product carbon dioxide (CO 2 ). The breathing reflex is triggered by CO 2 concentration in the blood, not by the oxygen concentration, so even a small buildup of CO 2 in the inhaled gas quickly becomes intolerable; if a person tries to directly rebreathe their exhaled breathing gas, they will soon feel an acute sense of suffocation , so rebreathers must remove

6000-542: Is wasted. Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen. However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of hypercapnia , or carbon dioxide toxicity. A high ventilation rate

6120-419: The decompression status of the diver and record the dive profile . As a person breathes, the body consumes oxygen and produces carbon dioxide . Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen. The oxygen metabolised is generally about 4% to 5% of

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6240-447: The CO 2 in a component known as a carbon dioxide scrubber . By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved. The endurance of a rebreather, the duration for which it can be safely and comfortably used, is dependent on the oxygen supply at the oxygen consumption rate of the user, and

6360-755: The Earth weight of 3.1 kg) on the Moon). Similar systems have been used by Space Shuttle astronauts, and are currently used by International Space Station crews. The primary life support system for the EMU suit used on the Space Shuttle and International Space Station is manufactured by Hamilton Sundstrand . It is mounted to the back of the Hard Upper Torso (HUT) assembly. Oxygen (O 2 ), carbon dioxide (CO 2 ) and water vapor are drawn from

6480-574: The Oxygen Purge System (OPS), mounted on top of the PLSS, immediately behind the astronaut's helmet. The OPS maintained suit pressure and removed carbon dioxide, heat and water vapor through a continuous, one-way air flow vented to space. When activated, the OPS provided oxygen to a separate inlet on the pressure suit, once a vent valve on a separate suit outlet was manually opened. The OPS provided

6600-551: The air that the staff breathe, and at high altitude, where the partial pressure of oxygen is low, for high altitude mountaineering. In aerospace there are applications in unpressurised aircraft and for high altitude parachute drops, and above the Earth's atmosphere, in space suits for extra-vehicular activity . Similar technology is used in life-support systems in submarines, submersibles, atmospheric diving suits , underwater and surface saturation habitats, spacecraft, and space stations, and in gas reclaim systems used to recover

6720-408: The air; the cross-section of the flow is only determined by the shape of the channel on the lower side, and is variable depending on the depth of liquid in the channel. Techniques appropriate for a fixed cross-section of flow in a pipe are not useful in open channels. Measuring flow in waterways is an important open-channel flow application; such installations are known as stream gauges . The level of

6840-419: The ambient pressure breathing volume components, usually called the breathing loop in a circulating flow rebreather, and the make-up gas supply and control system. The counterlung is an airtight bag of strong flexible material that holds the volume of the exhaled gas until it is inhaled again. There may be a single counterlung, or one on each side of the scrubber, which allows a more even flow rate of gas through

6960-441: The ambient pressure breathing volume, either continuously, or when the user operates the oxygen addition valve, or via a demand valve in an oxygen rebreather, when the volume of gas in the breathing circuit becomes low and the pressure drops, or in an electronically controlled mixed gas rebreather, after a sensor has detected insufficient oxygen partial pressure, and activates a solenoid valve. Valves are needed to control gas flow in

7080-426: The application and industry, but might include gallons (U.S. or imperial) per minute, liters per second, liters per m per hour, bushels per minute or, when describing river flows, cumecs (cubic meters per second) or acre-feet per day. In oceanography a common unit to measure volume transport (volume of water transported by a current for example) is a sverdrup (Sv) equivalent to 10  m /s. A primary flow element

7200-475: The astronaut's face. By delivering oxygen to the helmet and drawing gas from the extremities, the suit is designed to ensure that the suit occupant breathes the freshest possible oxygen. The operating pressure of the space suit is maintained at 4.3  psi (30  kPa ) (0.3 atm ~ one third of Earth atmospheric pressure ) during extravehicular operations , and 0.7 psi (4.8 kPa) relative to external pressure while in intravehicular mode ( i.e. , inside

7320-470: The breathing gas is a mixture of oxygen and metabolically inactive diluent gas. These can be divided into semi-closed circuit, where the supply gas is a breathable mixture containing oxygen and inert diluents, usually nitrogen and helium, and which is replenished by adding more of the mixture as the oxygen is used up, sufficient to maintain a breathable partial pressure of oxygen in the loop, and closed circuit rebreathers, where two parallel gas supplies are used:

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7440-713: The breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases. Rebreathers are used in many environments: underwater, diving rebreathers are a type of self-contained underwater breathing apparatus which have provisions for both a primary and emergency gas supply. On land they are used in industrial applications where poisonous gases may be present or oxygen may be absent, firefighting , where firefighters may be required to operate in an atmosphere immediately dangerous to life and health for extended periods, in hospital anaesthesia breathing systems to supply controlled concentrations of anaesthetic gases to patients without contaminating

7560-692: The breathing volume, and gas feed from the storage container. They include: Oxygen sensors may be used to monitor partial pressure of oxygen in mixed gas rebreathers to ensure that it does not fall outside the safe limits, but are generally not used on oxygen rebreathers, as the oxygen content is fixed at 100%, and its partial pressure varies only with the ambient pressure. Re breathers can be primarily categorised as diving rebreathers, intended for hyperbaric use, and other rebreathers used at pressures from slightly more than normal atmospheric pressure at sea level to significantly lower ambient pressure at high altitudes and in space. Diving rebreathers must often deal with

7680-406: The capacity of the scrubber to remove carbon dioxide at the rate it is produced by the user. These variables are closely linked, as the carbon dioxide is a product of metabolic oxygen consumption , though not the only product. This is independent of depth, except for work of breathing increase due to gas density increase. There are two basic arrangements controlling the flow of breathing gas inside

7800-401: The carbon dioxide absorbent: 4KO 2 + 2CO 2 = 2K 2 CO 3 + 3O 2 . A small volume oxygen cylinder is needed to fill and purge the loop at the start of use. This technology may be applied to both oxygen and mixed gas rebreathers, and can be used for diving and other applications. Potassium superoxide reacts vigorously with liquid water, releasing considerable heat and oxygen, and causing

7920-454: The carbon dioxide from the breathing air, and circulated water in an open loop through a liquid-cooled garment , expelling the water into space, where it turned to ice crystals. Some of the water was also used to remove excess heat from the astronaut's breathing air, and collected for dumping into the spacecraft 's wastewater tank after an EVA. The PLSS also contained a radio transceiver and antenna for communications, which were relayed through

8040-445: The channel and measure the velocity from above and then use ultrasound to measure the depth of the water from above. Radar devices can only measure surface velocities, whereas laser-based devices can measure velocities sub-surface. A known amount of dye (or salt ) per unit time is added to a flow stream. After complete mixing, the concentration is measured. The dilution rate equals the flow rate. Acoustic Doppler velocimetry (ADV)

8160-530: The circumference of the element, not just one point; this minimizes uneven wear on the impeller and its shaft. Thus these types of meters are recommended to be installed horizontally with its roller index pointing skywards. The Pelton wheel turbine (better described as a radial turbine ) translates the mechanical action of the Pelton wheel rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The Pelton wheel tends to have all

8280-416: The complications of avoiding hyperbaric oxygen toxicity, while normobaric and hypobaric applications can use the relatively trivially simple oxygen rebreather technology, where there is no requirement to monitor oxygen partial pressure during use providing the ambient pressure is sufficient. Rebreathers can also be subdivided by functional principle as closed circuit and semi-closed circuit rebreathers. This

8400-441: The cross sectional area of the device to vary in response to the flow, causing some measurable effect that indicates the rate. A rotameter is an example of a variable area meter, where a weighted "float" rises in a tapered tube as the flow rate increases; the float stops rising when area between float and tube is large enough that the weight of the float is balanced by the drag of fluid flow. A kind of rotameter used for medical gases

8520-486: The cross-sectional area yields a flow rate which can be integrated into volumetric flow. There are two types of area velocity flowmeter: (1) wetted; and (2) non-contact. Wetted area velocity sensors have to be typically mounted on the bottom of a channel or river and use Doppler to measure the velocity of the entrained particles. With depth and a programmed cross-section this can then provide discharge flow measurement. Non-contact devices that use laser or radar are mounted above

8640-473: The diluent, to provide the bulk of the gas, and which is recycled, and oxygen, which is metabolically expended. Carbon dioxide is considered a waste product, and in a correctly functioning rebreather, is effectively removed when the gas passes through the scrubber. There have been a few rebreather designs (e.g. the Oxylite) which use potassium superoxide , which gives off oxygen as it absorbs carbon dioxide, as

8760-439: The diver continues to inhale. Oxygen can also be added manually by a button which activates the demand valve. Some simple oxygen rebreathers had no automatic supply system, but only the manual feed valve, and the diver had to operate the valve at intervals to refill the breathing bag as the volume of oxygen decreased below a comfortable level. All rebreathers other than oxygen rebreathers may be considered mixed gas rebreathers, as

8880-411: The extremities of the suit by the liquid cooling and ventilation garment or LCVG , which sends the gas to the PLSS. When gas enters the PLSS, activated charcoal removes odors and lithium hydroxide (LiOH) removes carbon dioxide. Next, the gas passes through a fan which maintains a flow rate of about six cubic feet per minute. A sublimator then condenses water vapor, which is removed by a "slurper" and

9000-447: The flow of surface waters (springs, streams, and rivers), industrial discharges, and sewage. Of these, weirs are used on flow streams with low solids (typically surface waters), while flumes are used on flows containing low or high solids contents. The cross-sectional area of the flow is calculated from a depth measurement and the average velocity of the flow is measured directly (Doppler and propeller methods are common). Velocity times

9120-663: The flow profile and fluid conditions. Turbine flowmeters are commonly best suited for low viscosity, as large particulate can damage the rotor. When choosing a meter for an application that requires particulate flowing through the pipe, it is best to use a meter without moving parts such as a Magnetic flowmeters . Fire meters are a specialized type of turbine meter with approvals for the high flow rates required in fire protection systems. They are often approved by Underwriters Laboratories (UL) or Factory Mutual (FM) or similar authorities for use in fire protection. Portable turbine meters may be temporarily installed to measure water used from

9240-421: The flow rate of large pipeworks. Differential pressure produced by a Dall tube is higher than Venturi tube and nozzle, all of them having same throat diameters. A pitot tube is used to measure fluid flow velocity. The tube is pointed into the flow and the difference between the stagnation pressure at the tip of the probe and the static pressure at its side is measured, yielding the dynamic pressure from which

9360-412: The flow the higher the frequency and the voltage output. The paddle wheel meter is designed to be inserted into a pipe fitting, either 'in-line' or insertion style. These are available with wide range of fittings styles, connection methods and materials such as PVDF, polypropylene, and stainless steel. Similar to turbine meters, the paddle wheel meter require a minimum run of straight pipe before and after

9480-416: The flow traveling around it with the inlet flow focused on the blades by a jet. The original Pelton wheels were used for the generation of power and consisted of a radial flow turbine with "reaction cups" which not only move with the force of the water on the face but return the flow in opposite direction using this change of fluid direction to further increase the efficiency of the turbine . Flow through

9600-470: The flow, much like a ducted fan; it can be considered a type of turbine flowmeter. They are commonly referred to as helix meters, and are popular at larger sizes. A single jet meter consists of a simple impeller with radial vanes, impinged upon by a single jet. They are increasing in popularity in the UK at larger sizes and are commonplace in the EU . Paddle wheel flowmeters consist of three primary components:

9720-413: The fluid velocity is calculated using Bernoulli's equation . A volumetric rate of flow may be determined by measuring the velocity at different points in the flow and generating the velocity profile. Averaging pitot tubes (also called impact probes) extend the theory of pitot tube to more than one dimension. A typical averaging pitot tube consists of three or more holes (depending on the type of probe) on

9840-410: The gas composition other than removing the carbon dioxide. In some rebreathers the oxygen cylinder has oxygen supply mechanisms in parallel. One is constant flow ; the other is a manual on-off valve called a bypass valve; both feed into the same hose which feeds the counterlung. Others are supplied via a demand valve on the counterlung. This will add gas at any time that the counterlung is emptied and

9960-435: The granules by size, or by moulding granules at a consistent size and shape. Gas flow through the scrubber may be in one direction in a loop rebreather, or both ways in a pendulum rebreather. The scrubber canister generally has an inlet on one side and an outlet on the other side. A typical absorbent is soda lime , which is made up of calcium hydroxide Ca(OH) 2 , and sodium hydroxide NaOH. The main component of soda lime

10080-475: The inspired volume at normal atmospheric pressure , or about 20% of the available oxygen in the air at sea level . Exhaled air at sea level contains roughly 13.5% to 16% oxygen. The situation is even more wasteful of oxygen when the oxygen fraction of the breathing gas is higher, and in underwater diving, the compression of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas

10200-401: The intermediate reaction, the carbonic acid reacts exothermically with sodium hydroxide to form sodium carbonate and water: H 2 CO 3 + 2NaOH –> Na 2 CO 3 + 2H 2 O + heat. In the final reaction, the sodium carbonate reacts with the slaked lime (calcium hydroxide) to form calcium carbonate and sodium hydroxide: Na 2 CO 3 + Ca(OH) 2 –> CaCO 3 + 2NaOH. The sodium hydroxide

10320-435: The internal pressure is maintained at one atmosphere, there is no risk of acute oxygen toxicity. This is an underwater diving application, but has more in common with industrial applications than with ambient pressure scuba rebreathers. Different design criteria apply to SCBA rebreathers for use only out of the water: Mountaineering rebreathers provide oxygen at a higher concentration than available from atmospheric air in

10440-534: The large volumes of helium used in saturation diving . The recycling of breathing gas comes at the cost of technological complexity and specific hazards, some of which depend on the application and type of rebreather used. Mass and bulk may be greater or less than open circuit depending on circumstances. Electronically controlled diving rebreathers may automatically maintain a partial pressure of oxygen between programmable upper and lower limits, or set points, and be integrated with decompression computers to monitor

10560-444: The material's density . The density of a liquid is almost independent of conditions. This is not the case for gases, the densities of which depend greatly upon pressure, temperature and to a lesser extent, composition. When gases or liquids are transferred for their energy content, as in the sale of natural gas , the flow rate may also be expressed in terms of energy flow, such as gigajoule per hour or BTU per day. The energy flow rate

10680-418: The measured differential pressure is linearly proportional to the flow and to the fluid viscosity. Such flow is called viscous drag flow or laminar flow, as opposed to the turbulent flow measured by orifice plates, Venturis and other meters mentioned in this section, and is characterized by Reynolds numbers below 2000. The primary flow element may consist of a single long capillary tube, a bundle of such tubes, or

10800-421: The measuring element does not occupy or severely restrict the entire path of flow. The flow direction is generally straight through the meter, allowing for higher flow rates and less pressure loss than displacement-type meters. They are the meter of choice for large commercial users, fire protection, and as master meters for the water distribution system . Strainers are generally required to be installed in front of

10920-450: The measuring tip arranged in a specific pattern. More holes allow the instrument to measure the direction of the flow velocity in addition to its magnitude (after appropriate calibration). Three holes arranged in a line allow the pressure probes to measure the velocity vector in two dimensions. Introduction of more holes, e.g. five holes arranged in a "plus" formation, allow measurement of the three-dimensional velocity vector. Cone meters are

11040-405: The meter and strikes the nutating disk, which is eccentrically mounted. The disk must then "wobble" or nutate about the vertical axis, since the bottom and the top of the disk remain in contact with the mounting chamber. A partition separates the inlet and outlet chambers. As the disk nutates, it gives direct indication of the volume of the liquid that has passed through the meter as volumetric flow

11160-476: The meter to protect the measuring element from gravel or other debris that could enter the water distribution system. Turbine meters are generally available for 4 to 30 cm ( 1 + 1 ⁄ 2 –12 in) or higher pipe sizes. Turbine meter bodies are commonly made of stainless steel, bronze, cast Iron, or ductile iron. Internal turbine elements can be plastic or non-corrosive metal alloys. They are accurate in normal working conditions but are greatly affected by

11280-521: The outlet port. Meanwhile, fluid entering the inlet port will be driven into the measurement chamber of side A, which is now open. The teeth on side B will now close off the fluid from entering side B. This cycle continues as the gears rotate and fluid is metered through alternating measurement chambers. Permanent magnets in the rotating gears can transmit a signal to an electric reed switch or current transducer for flow measurement. Though claims for high performance are made, they are generally not as precise as

11400-415: The paddle wheel sensor, the pipe fitting and the display/controller. The paddle wheel sensor consists of a freely rotating wheel/impeller with embedded magnets which are perpendicular to the flow and will rotate when inserted in the flowing medium. As the magnets in the blades spin past the sensor, the paddle wheel meter generates a frequency and voltage signal which is proportional to the flow rate. The faster

11520-400: The personnel under pressure in the accommodation chambers and closed diving bell. It includes the following components: The life support system for the bell provides and monitors the main supply of breathing gas, and the control station monitors the deployment and communications with the divers. Primary gas supply, power and communications to the bell are through a bell umbilical, made up from

11640-402: The photo, benefit from easier field repair if a tear or hole while helical corrugations allow efficient drainage after cleaning. Breathing hoses are usually long enough to connect the apparatus to the user's head in all attitudes of their head, but should not be unnecessarily long, which will cause additional weight, hydrodynamic drag , risk snagging on things, or contain excess dead space in

11760-412: The piston chamber. Through a gear mechanism and, sometimes, a magnetic drive, a needle dial and odometer type display are advanced. An oval gear meter is a positive displacement meter that uses two or more oblong gears configured to rotate at right angles to one another, forming a T shape. Such a meter has two sides, which can be called A and B. No fluid passes through the center of the meter, where

11880-697: The pressure loss of fluids as they pass that constriction, or by measuring static and stagnation pressures to derive the dynamic pressure . A Venturi meter constricts the flow in some fashion, and pressure sensors measure the differential pressure before and within the constriction. This method is widely used to measure flow rate in the transmission of gas through pipelines , and has been used since Roman Empire times. The coefficient of discharge of Venturi meter ranges from 0.93 to 0.97. The first large-scale Venturi meters to measure liquid flows were developed by Clemens Herschel , who used them to measure small and large flows of water and wastewater beginning at

12000-403: The pressurized spacecraft). Technologies being considered for application in future PLSSs include pressure swing adsorption (PSA), a process by which CO 2 can be separated from gas more efficiently, and through a repeatable process, as opposed to the current LiOH canisters, which become saturated with each use, and are limited to around eight hours. By regenenerating the sorbent during EVA,

12120-418: The rebreather, known as the pendulum and loop systems. In the pendulum configuration, the user inhales gas from the counterlung through a breathing hose, and exhaled gas returns to the counterlung by flowing back through the same hose. The scrubber is usually between the breathing hose and the counterlung bag, and gas flow is bi-directional. All of the flow passages between the user and the active absorbent in

12240-467: The scrubber are dead space – volume containing gas which is rebreathed without modification by the rebreather. The dead space increases as the absorbent is depleted. Breathing hose volume must be minimised to limit dead space. In the loop configuration, the user inhales gas through one hose, and exhales through a second hose. Exhaled gas flows into the scrubber from one side, and exits at the other side. There may be one large counterlung, on either side of

12360-621: The scrubber contents from freezing, and helps reduce heat loss from the user. Both chemical and compressed gas oxygen have been used in experimental closed-circuit oxygen systems – the first on Mount Everest in 1938 . The 1953 expedition used closed-circuit oxygen equipment developed by Tom Bourdillon and his father for the first assault team of Bourdillon and Evans ; with one "dural" 800l compressed oxygen cylinder and soda lime canister (the second (successful) assault team of Hillary and Tenzing used open-circuit equipment). Similar requirement and working environment to mountaineering, but weight

12480-463: The scrubber, or two smaller counterlungs, one on each side of the scrubber. Flow is in one direction, enforced by non-return valves, which are usually in the breathing hoses where they join the mouthpiece. Only the flow passage in the mouthpiece before the split between inhalation and exhalation hoses is dead space, and this is not affected by hose volume. There are some components that are common to almost all personal portable rebreathers. These include

12600-436: The scrubber, which can reduce work of breathing and improve scrubber efficiency by a more consistent dwell time . The scrubber is a container filled with carbon dioxide absorbent material, mostly strong bases , through which the exhaled gas passes to remove the carbon dioxide. The absorbent may be granular or in the form of a moulded cartridge. Granular absorbent may be manufactured by breaking up lumps of lime and sorting

12720-497: The sensor. Flow displays and controllers are used to receive the signal from the paddle wheel meter and convert it into actual flow rate or total flow values. The processed signal can be used to control the process, generate an alarm, send signals to external etc. Paddle wheel flowmeters (also known as Pelton wheel sensors) offer a relatively low cost, high accuracy option for many flow system applications, typically with water or water-like fluids. A multiple jet or multijet meter

12840-442: The service, they may be made of a flexible polymer, an elastomer , a fibre or cloth reinforced elastomer, or elastomer covered with a woven fabric for reinforcement or abrasion resistance. If the woven layer is bonded to the outside surface it protects the rubber from damage from scrapes but makes it more difficult to wash off contaminants. Breathing hoses typically come in two types of corrugation. Annular corrugations, as depicted in

12960-409: The size and weight of the sorbent canister can be greatly reduced. PSA accomplishes this by venting CO 2 and water vapor into space. Rebreather A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen

13080-426: The sliding vane design. Gear meters differ from oval gear meters in that the measurement chambers are made up of the gaps between the teeth of the gears. These openings divide up the fluid stream and as the gears rotate away from the inlet port, the meter's inner wall closes off the chamber to hold the fixed amount of fluid. The outlet port is located in the area where the gears are coming back together. The fluid

13200-580: The spacecraft's communication system to Earth. PLSS controls were provided in the Remote Control Unit (RCU) mounted on the astronaut's chest. Oxygen and water were rechargeable for multiple EVAs from the spacecraft's environmental control system. Lunar surface EVA times for the first four missions (Apollo 11 through 14) were limited to 4 hours, with oxygen stored at 1,020 pounds per square inch (7.0 MPa), 3.0 pounds (1.4 kg) of lithium hydroxide, 8.5 pounds (3.9 liters) of cooling water, and

13320-505: The symbol m ˙ {\displaystyle {\dot {m}}} . For a fluid having density ρ {\displaystyle \rho } , mass and volumetric flow rates may be related by m ˙ = ρ Q {\displaystyle {\dot {m}}=\rho Q} . Gases are compressible and change volume when placed under pressure, are heated or are cooled. A volume of gas under one set of pressure and temperature conditions

13440-429: The teeth of the two gears always mesh. On one side of the meter (A), the teeth of the gears close off the fluid flow because the elongated gear on side A is protruding into the measurement chamber, while on the other side of the meter (B), a cavity holds a fixed volume of fluid in a measurement chamber. As the fluid pushes the gears, it rotates them, allowing the fluid in the measurement chamber on side B to be released into

13560-420: The time gives the flow rate. For continuous measurements, we need a system of continually filling and emptying buckets to divide the flow without letting it out of the pipe. These continuously forming and collapsing volumetric displacements may take the form of pistons reciprocating in cylinders, gear teeth mating against the internal wall of a meter or through a progressive cavity created by rotating oval gears or

13680-489: The traverse of the current meters. Methods for testing hydroelectric turbines are given in IEC standard 41. Such flow measurements are often commercially important when testing the efficiency of large turbines. There are several types of flowmeter that rely on Bernoulli's principle . The pressure is measured either by using laminar plates, an orifice, a nozzle, or a Venturi tube to create an artificial constriction and then measure

13800-416: The type include: A cryogenic rebreather removes the carbon dioxide by freezing it out in a "snow box" by the low temperature produced as liquid oxygen evaporates to replace the oxygen used. This may be compared with some applications of open-circuit breathing apparatus: The widest variety of rebreather types is used in diving, as the consequences of breathing under pressure complicate the requirements, and

13920-429: The velocity of fluid over a known area. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope. Both gas and liquid flow can be measured in physical quantities of kind volumetric flow rate or mass flow rates , with respective SI units such as cubic meters per second or kilograms per second, respectively. These measurements are related by

14040-402: The very end of the 19th century. An orifice plate is a plate with a hole through it, placed perpendicular to the flow; it constricts the flow, and measuring the pressure differential across the constriction gives the flow rate. It is basically a crude form of Venturi meter , but with higher energy losses. There are three type of orifice: concentric, eccentric, and segmental. The Dall tube

14160-391: The water is measured at a designated point behind weir or in flume using various secondary devices (bubblers, ultrasonic, float, and differential pressure are common methods). This depth is converted to a flow rate according to a theoretical formula of the form Q = K H X {\displaystyle Q=KH^{X}} where Q {\displaystyle Q}

14280-425: The water of the soda lime and formed carbonic acid, changing the pH from basic to acid, as the change of colour shows that the absorbent has reached saturation with carbon dioxide and must be changed. The carbon dioxide combines with water or water vapor to produce a weak carbonic acid: CO 2 + H 2 O –> H 2 CO 3 . This reacts with the hydroxides to produce carbonates and water in an exothermic reaction. In

14400-598: Was tested at the Houston Flight Center by James P. Lucas, working for Hamilton Standard , and by various astronauts in neutral buoyancy tanks at Dallas. It was tested in space for the first time by Rusty Schweickart in a stand-up EVA in Earth orbit on Apollo 9 . His PLSS weighed 84 pounds (38 kg) on Earth, but only 14 lb (equivalent to the Earth weight of 6.4 kg) on the Moon. The OPS weighed 41 pounds (19 kg) on Earth (6.8 lb (equivalent to

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