Pressure regulator

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Oxygen and MAPP gas cylinders with two-stage pressure regulators Compressed gas cylinders.mapp and oxygen.triddle.jpg
Oxygen and MAPP gas cylinders with two-stage pressure regulators
Schematic diagram of pressure reducing regulator (A) and back-pressure regulator (B). The upper diagrams show the normal state for the valves, which is normally open for pressure reducers and normally closed for back-pressure valves.
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1. Pressure setting screw
2. Spring
3. Actuator
4. Inlet port (high pressure)
5. Outlet port (low pressure)
6. Valve body
7. Valve crown and seat Pressure regulators schematic.png
Schematic diagram of pressure reducing regulator (A) and back-pressure regulator (B). The upper diagrams show the normal state for the valves, which is normally open for pressure reducers and normally closed for back-pressure valves.
  • 1. Pressure setting screw
  • 2. Spring
  • 3. Actuator
  • 4. Inlet port (high pressure)
  • 5. Outlet port (low pressure)
  • 6. Valve body
  • 7. Valve crown and seat
Diagram symbols for pressure reduction and back pressure regulators. The conceptual difference is mainly in which side the feedback is taken from. Pressure regulators symbols.png
Diagram symbols for pressure reduction and back pressure regulators. The conceptual difference is mainly in which side the feedback is taken from.

A pressure regulator is a valve that controls the pressure of a fluid to a desired value, using negative feedback from the controlled pressure. Regulators are used for gases and liquids, and can be an integral device with a pressure setting, a restrictor and a sensor all in the one body, or consist of a separate pressure sensor, controller and flow valve.

Contents

Two types are found: The pressure reduction regulator and the back-pressure regulator.

Both types of regulator use feedback of the regulated pressure as input to the control mechanism, and are commonly actuated by a spring loaded diaphragm or piston reacting to changes in the feedback pressure to control the valve opening, and in both cases the valve should be opened only enough to maintain the set regulated pressure. The actual mechanism may be very similar in all respects except the placing of the feedback pressure tap. [2] As in other feedback control mechanisms, the level of damping is important to achieve a balance between fast response to a change in the measured pressure, and stability of output. Insufficient damping may lead to hunting oscillation of the controlled pressure, while excessive friction of moving parts may cause hysteresis.

Pressure reducing regulator

Operation

A pressure reducing regulator's primary function is to match the flow of gas through the regulator to the demand for fluid placed upon it, whilst maintaining a sufficiently constant output pressure. If the load flow decreases, then the regulator flow must decrease as well. If the load flow increases, then the regulator flow must increase in order to keep the controlled pressure from decreasing due to a shortage of fluid in the pressure system. It is desirable that the controlled pressure does not vary greatly from the set point for a wide range of flow rates, but it is also desirable that flow through the regulator is stable and the regulated pressure is not subject to excessive oscillation.[ citation needed ]

A pressure regulator includes a restricting element, a loading element, and a measuring element:

In the pictured single-stage regulator, a force balance is used on the diaphragm to control a poppet valve in order to regulate pressure. With no inlet pressure, the spring above the diaphragm pushes it down on the poppet valve, holding it open. Once inlet pressure is introduced, the open poppet allows flow to the diaphragm and pressure in the upper chamber increases, until the diaphragm is pushed upward against the spring, causing the poppet to reduce flow, finally stopping further increase of pressure. By adjusting the top screw, the downward pressure on the diaphragm can be increased, requiring more pressure in the upper chamber to maintain equilibrium. In this way, the outlet pressure of the regulator is controlled.[ citation needed ]






Single stage regulator

Single-stage pressure regulator Single-stage-regulator.svg
Single-stage pressure regulator

High pressure gas from the supply enters the regulator through the inlet port. The inlet pressure gauge will indicate this pressure. The gas then passes through the normally open pressure control valve orifice and the downstream pressure rises until the valve actuating diaphragm is deflected sufficiently to close the valve, preventing any more gas from entering the low pressure side until the pressure drops again. The outlet pressure gauge will indicate this pressure.[ citation needed ]

The outlet pressure on the diaphragm and the inlet pressure and poppet spring force on the upstream part of the valve hold the diaphragm/poppet assembly in the closed position against the force of the diaphragm loading spring. If the supply pressure falls, the closing force due to supply pressure is reduced, and downstream pressure will rise slightly to compensate. Thus, if the supply pressure falls, the outlet pressure will increase, provided the outlet pressure remains below the falling supply pressure. This is the cause of end-of-tank dump where the supply is provided by a pressurized gas tank.[ citation needed ] The operator can compensate for this effect by adjusting the spring load by turning the knob to restore outlet pressure to the desired level. With a single stage regulator, when the supply pressure gets low, the lower inlet pressure causes the outlet pressure to climb. If the diaphragm loading spring compression is not adjusted to compensate, the poppet can remain open and allow the tank to rapidly dump its remaining contents.[ citation needed ]

Double stage regulator

Two-stage pressure regulator Two-stage-regulator.svg
Two-stage pressure regulator

Two stage regulators are two regulators in series in the same housing that operate to reduce the pressure progressively in two steps instead of one. The first stage, which is preset, reduces the pressure of the supply gas to an intermediate stage; gas at that pressure passes into the second stage. The gas emerges from the second stage at a pressure (working pressure) set by user by adjusting the pressure control knob at the diaphragm loading spring. Two stage regulators may have two safety valves, so that if there is any excess pressure between stages due to a leak at the first stage valve seat the rising pressure will not overload the structure and cause an explosion.[ citation needed ]

An unbalanced single stage regulator may need frequent adjustment. As the supply pressure falls, the outlet pressure may change, necessitating adjustment. In the two stage regulator, there is improved compensation for any drop in the supply pressure.[ citation needed ]

Applications

Pressure reducing regulators

Air compressors

Air compressors are used in industrial, commercial, and home workshop environments to perform an assortment of jobs including blowing things clean; running air powered tools; and inflating things like tires, balls, etc. Regulators are often used to adjust the pressure coming out of an air receiver (tank) to match what is needed for the task. Often, when one large compressor is used to supply compressed air for multiple uses (often referred to as "shop air" if built as a permanent installation of pipes throughout a building), additional regulators will be used to ensure that each separate tool or function receives the pressure it needs. This is important because some air tools, or uses for compressed air, require pressures that may cause damage to other tools or materials.[ citation needed ]

Aircraft

Pressure regulators are found in aircraft cabin pressurization, canopy seal pressure control, potable water systems, and waveguide pressurization. [3]

Aerospace

Aerospace pressure regulators have applications in propulsion pressurant control for reaction control systems (RCS) and Attitude Control Systems (ACS), where high vibration, large temperature extremes and corrosive fluids are present. [4]

Cooking

Pressurized vessels can be used to cook food much more rapidly than at atmospheric pressure, as the higher pressure raises the boiling point of the contents. All modern pressure cookers will have a pressure regulator valve and a pressure relief valve as a safety mechanism to prevent explosion in the event that the pressure regulator valve fails to adequately release pressure. Some older models lack a safety release valve[ citation needed ]. Most home cooking models are built to maintain a low and high pressure setting. These settings are usually 7 to 15 pounds per square inch (0.48 to 1.03 bar). Almost all home cooking units will employ a very simple single-stage pressure regulator. Older models will simply use a small weight on top of an opening that will be lifted by excessive pressure to allow excess steam to escape. Newer models usually incorporate a spring-loaded valve that lifts and allows pressure to escape as pressure in the vessel rises. Some pressure cookers will have a quick release setting on the pressure regulator valve that will, essentially, lower the spring tension to allow the pressure to escape at a quick, but still safe rate. Commercial kitchens also use pressure cookers, in some cases using oil based pressure cookers to quickly deep fry fast food. Pressure vessels of this sort can also be used as autoclaves to sterilize small batches of equipment and in home canning operations.[ citation needed ]

Water pressure reduction

Pressure regulator for domestic water supply. Outlet pressure is set with the blue handwheel and shown on the vertical scale. Optima Druckminderer 315-4516.jpg
Pressure regulator for domestic water supply. Outlet pressure is set with the blue handwheel and shown on the vertical scale.

A water pressure regulating valve limits inflow by dynamically changing the valve opening so that when less pressure is on the outside, the valve opens up fully, and too much pressure on the outside causes the valve to shut. In a no pressure situation, where water could flow backwards, it won't be impeded. A water pressure regulating valve does not function as a check valve.[ citation needed ][ clarification needed ]

They are used in applications where the water pressure is too high at the end of the line to avoid damage to appliances or pipes.

Welding and cutting

Oxy-fuel welding and cutting processes require gases at specific pressures, and regulators will generally be used to reduce the high pressures of storage cylinders to those usable for cutting and welding. Oxygen and fuel gas regulators usually have two stages: The first stage of the regulator releases the gas at a constant pressure from the cylinder despite the pressure in the cylinder becoming less as the gas is released. The second stage of the regulator controls the pressure reduction from the intermediate pressure to low pressure. The final flow rate may be adjusted at the torch. The regulator assembly usually has two pressure gauges, one indicating cylinder pressure, the other indicating delivery pressure. Inert gas shielded arc welding also uses gas stored at high pressure provided through a regulator. There may be a flow gauge calibrated to the specific gas.[ citation needed ]

Propane/LP gas

All propane and LP gas applications require the use of a regulator. Because pressures in propane tanks can fluctuate significantly with temperature, regulators must be present to deliver a steady pressure to downstream appliances. These regulators normally compensate for tank pressures between 30–200 pounds per square inch (2.1–13.8 bar) and commonly deliver 11 inches water column 0.4 pounds per square inch (28 mbar) for residential applications and 35 inches of water column 1.3 pounds per square inch (90 mbar) for industrial applications. Propane regulators differ in size and shape, delivery pressure and adjustability, but are uniform in their purpose to deliver a constant outlet pressure for downstream requirements. Common international settings for domestic LP gas regulators are 28 mbar for butane and 37 mbar for propane.

Gas powered vehicles

All vehicular motors that run on compressed gas as a fuel (internal combustion engine or fuel cell electric power train) require a pressure regulator to reduce the stored gas (CNG or Hydrogen) pressure from 700, 500, 350 or 200 bar (or 70, 50, 35 and 20 MPa) to operating pressure.[ citation needed ])

Recreational vehicles

For recreational vehicles with plumbing, a pressure regulator is required to reduce the pressure of an external water supply connected to the vehicle plumbing, as the supply may be a much higher elevation than the campground, and water pressure depends on the height of the water column. Without a pressure regulator, the intense pressure encountered at some campgrounds in mountainous areas may be enough to burst the camper's water pipes or unseat the plumbing joints, causing flooding. Pressure regulators for this purpose are typically sold as small screw-on accessories that fit inline with the hoses used to connect an RV to the water supply, which are almost always screw-thread-compatible with the common garden hose.[ citation needed ]

Breathing gas supply

Two-gauge pressure regulator connected to gas cylinder used for breathing gas supply Depiction of a two-gauge pressure regulator connected to a cylinder.png
Two-gauge pressure regulator connected to gas cylinder used for breathing gas supply

Pressure regulators are used with diving cylinders for Scuba diving. The tank may contain pressures in excess of 3,000 pounds per square inch (210 bar), which could cause a fatal barotrauma injury to a person breathing it directly. A demand controlled regulator provides a flow of breathing gas at the ambient pressure (which varies by depth in the water). Pressure reducing regulators are also use to supply breathing gas to surface-supplied divers, [5] and people who use self-contained breathing apparatus (SCBA) for rescue and hazmat work on land. The interstage pressure for SCBA at normal atmospheric pressure can generally be left constant at a factory setting, but for surface supplied divers it is controlled by the gas panel operator, depending on the diver depth and flow rate requirements. Supplementary oxygen for high altitude flight in unpressurised aircraft and medical gases are also commonly dispensed through pressure reducing regulators from high-pressure storage. [6] [7]

Supplementary oxygen may also be dispensed through a regulator which both reduces the pressure, and supplies the gas at a metered flow rate, to be mixed with ambient air. [8] One way of producing a constant mass flow at variable ambient pressure is to use a choked flow, where the flow through the metering orifice is sonic. For a given gas in choked flow, the mass flow rate may be controlled by setting the orifice size or the upstream pressure. To produce a choked flow in oxygen, the absolute pressure ratio of upstream and downstream gas must exceed 1.893 at 20 °C. At normal atmospheric pressure this requires an upstream pressure of more than 1.013 × 1.893 = 1.918 bar. A typical nominal regulated gauge pressure from a medical oxygen regulator is 3.4 bars (50 psi), for an absolute pressure of approximately 4.4 bar and a pressure ratio of about 4.4 without back pressure, so they will have choked flow in the metering orifices for a downstream (outlet) pressure of up to about 2.3 bar absolute. This type of regulator commonly uses a rotor plate with calibrated orifices and detents to hold it in place when the orifice corresponding to the desired flow rate is selected. This type of regulator may also have one or two uncalibrated takeoff connections from the intermediate pressure chamber with diameter index safety system (DISS) or similar connectors to supply gas to other equipment, and the high pressure connection is commonly a pin index safety system (PISS) yoke clamp. [9] Similar mechanisms can be used for flow rate control for aviation and mountaineering regulators.

Mining industry

As the pressure in water pipes builds rapidly with depth, underground mining operations require a fairly complex water system with pressure reducing valves. These devices must be installed at a certain vertical interval, usually 600 feet (180 m).[ citation needed ] Without such valves, pipes could burst and pressure would be too great for equipment operation.

Natural gas industry

Pressure regulators are used extensively within the natural gas industry. Natural gas is compressed to high pressures in order to be distributed throughout the country through large transmission pipelines. The transmission pressure can be over 1,000 pounds per square inch (69 bar) and must be reduced through various stages to a usable pressure for industrial, commercial, and residential applications. There are three main pressure reduction locations in this distribution system. The first reduction is located at the city gate, whereas the transmission pressure is dropped to a distribution pressure to feed throughout the city. This is also the location where the odorless natural gas is odorized with mercaptan. The distribution pressure is further reduced at a district regulator station, located at various points in the city, to below 60 psig. The final cut would occur at the end users location. Generally, the end user reduction is taken to low pressures ranging from 0.25 psig to 5 psig. Some industrial applications can require a higher pressure.[ citation needed ]

Back-pressure regulators

Hyperbaric chambers

Where the pressure drop on a built-in breathing system exhaust system is too great, typically in saturation systems, a back-pressure regulator may be used to reduce the exhaust pressure drop to a safer and more manageable pressure. [10] [12]

Reclaim diving helmets

The depth at which most heliox breathing mixtures are used in surface-supplied diving is generally at least 5 bar above surface atmospheric pressure, and the exhaust gas from the diver must pass through a reclaim valve, which is a back-pressure valve activated by the increase in pressure in the diver's helmet above ambient pressure caused by diver exhalation. [13] [14] The reclaim gas hose which carries the exhaled gas back to the surface for recycling must not be at too great a pressure difference from the ambient pressure at the diver. An additional back-pressure regulator in this line allows finer setting of the reclaim valve for lower work of breathing at variable depths. [15]

See also

Related Research Articles

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A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. Scuba is an anacronym for self-contained underwater breathing apparatus. Although strictly speaking the scuba set is only the diving equipment that is required for providing breathing gas to the diver, general usage includes the harness or rigging by which it is carried and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge. In the looser sense, scuba set has been used to refer to all the diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment or scuba gear. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface-supplied diving systems and is allowed by the relevant legislation and code of practice.

<span class="mw-page-title-main">Valve</span> Flow control device

A valve is a device or natural object that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.

<span class="mw-page-title-main">Aqua-Lung</span> Original name for open-circuit scuba equipment

Aqua-Lung was the first open-circuit, self-contained underwater breathing apparatus to achieve worldwide popularity and commercial success. This class of equipment is now commonly referred to as a twin-hose diving regulator, or demand valve. The Aqua-Lung was invented in France during the winter of 1942–1943 by two Frenchmen: engineer Émile Gagnan and Jacques Cousteau, who was a Naval Lieutenant. It allowed Cousteau and Gagnan to film and explore underwater more easily.

<span class="mw-page-title-main">Ice diving</span> Underwater diving under ice

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<span class="mw-page-title-main">Check valve</span> Flow control device

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<span class="mw-page-title-main">Diving regulator</span> Mechanism that controls the pressure of a breathing gas supply for diving

A diving regulator or underwater diving regulator is a pressure regulator that controls the pressure of breathing gas for underwater diving. The most commonly recognised application is to reduce pressurized breathing gas to ambient pressure and deliver it to the diver, but there are also other types of gas pressure regulator used for diving applications. The gas may be air or one of a variety of specially blended breathing gases. The gas may be supplied from a scuba cylinder carried by the diver, in which case it is called a scuba regulator, or via a hose from a compressor or high-pressure storage cylinders at the surface in surface-supplied diving. A gas pressure regulator has one or more valves in series which reduce pressure from the source, and use the downstream pressure as feedback to control the delivered pressure, or the upstream pressure as feedback to prevent excessive flow rates, lowering the pressure at each stage.

<span class="mw-page-title-main">Diving air compressor</span> Machine used to compress breathing air for use by underwater divers

A diving air compressor is a breathing air compressor that can provide breathing air directly to a surface-supplied diver, or fill diving cylinders with high-pressure air pure enough to be used as a hyperbaric breathing gas. A low pressure diving air compressor usually has a delivery pressure of up to 30 bar, which is regulated to suit the depth of the dive. A high pressure diving compressor has a delivery pressure which is usually over 150 bar, and is commonly between 200 and 300 bar. The pressure is limited by an overpressure valve which may be adjustable.

<span class="mw-page-title-main">Rocketdyne J-2</span> Rocket engine

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<span class="mw-page-title-main">Scuba manifold</span> Scuba component used to functionally connect diving cylinders

A scuba manifold is a device incorporating one or more valves and one or more gas outlets with scuba regulator connections, used to connect two or more diving cylinders containing breathing gas, providing a greater amount of gas for longer dive times or deeper dives. An isolation manifold allows the connection between the cylinders to be closed in the case of a leak from one of the cylinders or its valve or regulator, conserving the gas in the other cylinder. Diving with two or more cylinders is often associated with technical diving. Almost all manifold assemblies include one cylinder valve for each cylinder, and the overwhelming majority are for two cylinders.

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<span class="mw-page-title-main">Instrumentation in petrochemical industries</span>

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Freeflow in underwater diving apparatus is a continuous flow of gas from a storage or supply unit. In scuba diving it is usually undesirable and considered a malfunction, while in surface supplied diving it may be a malfunction or a user selected option in demand systems, or the standard mode of operation in freeflow systems.

<span class="mw-page-title-main">Interspiro DCSC</span> Military semi-closed circuit passive addition diving rebreather

The Interspiro DCSC is a semi-closed circuit nitrox rebreather manufactured by Interspiro of Sweden for military applications. Interspiro was formerly a division of AGA and has been manufacturing self-contained breathing apparatus for diving, firefighting and rescue applications since the 1950s.

<span class="mw-page-title-main">Surface-supplied diving equipment</span> Equipment used specifically for surface supplied diving

Surface-supplied diving equipment (SSDE) is the equipment required for surface-supplied diving. The essential aspect of surface-supplied diving is that breathing gas is supplied from the surface, either from a specialised diving compressor, high-pressure gas storage cylinders, or both. In commercial and military surface-supplied diving, a backup source of surface-supplied breathing gas should always be present in case the primary supply fails. The diver may also wear a bailout cylinder which can provide self-contained breathing gas in an emergency. Thus, the surface-supplied diver is less likely to have an "out-of-air" emergency than a scuba diver using a single gas supply, as there are normally two alternative breathing gas sources available. Surface-supplied diving equipment usually includes communication capability with the surface, which improves the safety and efficiency of the working diver.

Diving hazards are the agents or situations that pose a threat to the underwater diver or their equipment. Divers operate in an environment for which the human body is not well suited. They face special physical and health risks when they go underwater or use high pressure breathing gas. The consequences of diving incidents range from merely annoying to rapidly fatal, and the result often depends on the equipment, skill, response and fitness of the diver and diving team. The classes of hazards include the aquatic environment, the use of breathing equipment in an underwater environment, exposure to a pressurised environment and pressure changes, particularly pressure changes during descent and ascent, and breathing gases at high ambient pressure. Diving equipment other than breathing apparatus is usually reliable, but has been known to fail, and loss of buoyancy control or thermal protection can be a major burden which may lead to more serious problems. There are also hazards of the specific diving environment, and hazards related to access to and egress from the water, which vary from place to place, and may also vary with time. Hazards inherent in the diver include pre-existing physiological and psychological conditions and the personal behaviour and competence of the individual. For those pursuing other activities while diving, there are additional hazards of task loading, of the dive task and of special equipment associated with the task.

<span class="mw-page-title-main">Built-in breathing system</span> System for supply of breathing gas on demand within a confined space

A built-in breathing system is a source of breathing gas installed in a confined space where an alternative to the ambient gas may be required for medical treatment, emergency use, or to minimise a hazard. They are found in diving chambers, hyperbaric treatment chambers, and submarines.

<span class="mw-page-title-main">Scuba cylinder valve</span> Valve controlling flow of breathing gas into and out of a scuba cylinder

A scuba cylinder valve or pillar valve is a high pressure manually operated screw-down shut off valve fitted to the neck of a scuba cylinder to control breathing gas flow to and from the pressure vessel and to provide a connection with the scuba regulator or filling whip. Cylinder valves are usually machined from brass and finished with a protective and decorative layer of chrome plating. A metal or plastic dip tube or valve snorkel screwed into the bottom of the valve extends into the cylinder to reduce the risk of liquid or particulate contaminants in the cylinder getting into the gas passages when the cylinder is inverted, and blocking or jamming the regulator.

<span class="mw-page-title-main">Diving rebreather</span> Closed or semi-closed circuit scuba

A Diving rebreather is an underwater breathing apparatus that absorbs the carbon dioxide of a diver's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the diver. 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, and, for covert military use by frogmen or observation of underwater life, to eliminate the bubbles produced by an open circuit system. A diving rebreather is generally understood to be a portable unit carried by the user, and is therefore a type of self-contained underwater breathing apparatus (scuba). A semi-closed rebreather carried by the diver may also be known as a gas extender. The same technology on a submersible or surface installation is more likely to be referred to as a life-support system.

<span class="mw-page-title-main">Mechanism of diving regulators</span> Arrangement and function of the components of regulators for underwater diving

The mechanism of diving regulators is the arrangement of components and function of gas pressure regulators used in the systems which supply breathing gases for underwater diving. Both free-flow and demand regulators use mechanical feedback of the downstream pressure to control the opening of a valve which controls gas flow from the upstream, high-pressure side, to the downstream, low-pressure side of each stage. Flow capacity must be sufficient to allow the downstream pressure to be maintained at maximum demand, and sensitivity must be appropriate to deliver maximum required flow rate with a small variation in downstream pressure, and for a large variation in supply pressure, without instability of flow. Open circuit scuba regulators must also deliver against a variable ambient pressure. They must be robust and reliable, as they are life-support equipment which must function in the relatively hostile seawater environment, and the human interface must be comfortable over periods of several hours.

References

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