Air, oxygen and helium gas blending system

Gas blending or gas mixing is the filling of diving cylinders with non-air breathing gases. Image File history File linksMetadata Download high resolution version (1296x972, 223 KB) Summary A gas blending system consisting of a blending panel with air inputs from 3 bank cylinders, located and blown by an electric powered compressor in the room behind, 3 inputs, for cascading, of oxygen J cylinders and... Image File history File linksMetadata Download high resolution version (1296x972, 223 KB) Summary A gas blending system consisting of a blending panel with air inputs from 3 bank cylinders, located and blown by an electric powered compressor in the room behind, 3 inputs, for cascading, of oxygen J cylinders and... 12 litre and 3 litre steel diving cylinders A diving cylinder or SCUBA tank is used to store and transport high pressure breathing gas as a component of an Aqua-Lung. ... Look up air in Wiktionary, the free dictionary. ... Air is the most common and only natural breathing gas. ...

Hazards

There are several hazards with gas mixing:

• cylinders are being filled with high pressure gas. So, if there is any damage or corrosion in the pressure vessel or valves of the cylinder, this is the occasion when they are most likely to fail.
• oxygen supports combustion. So, if it comes into contact with fuel and heat the three ingredients for a fire exist. Fires in the presence of high concentrations of oxygen burn more vigorously than those in air. A fire in the presence of high-pressure gas may cause cylinder failures.
• other high pressure equipment such as whips, compressors, gas banks and valves are being used, which can cause injury
• there are dangers from the fuel and electric power supplies of the compressor
• there are dangers from the moving parts of the compressor

It is possible for gas blenders to create toxic and dangerous gas mixes for divers. Too much or too little oxygen in the mix can be fatal for the diver. Oxygen analysers are used to measure the oxygen content of the mix. In good blending sites, this is done in the presence of the diver who acknowledges the contents by signing a log. Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface. ... Rust, the most familiar example of corrosion. ... A pressure vessel is a container designed to hold gases or liquids at a pressure different from the ambient pressure. ... A valve is a device that regulates the flow of fluids (either gases, fluidised solids, slurries or liquids) by opening, closing, or partially obstructing various passageways. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... Fuel is a material with one type of energy which can be transformed into another usable energy. ... In physics, heat is defined as energy in transit. ... A large bonfire. ... An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ...

It is possible that poisonous additives, such as carbon monoxide or hydrocarbon lubricants, will enter the cylinders from the diving air compressor. This is generally a problem with the compressor maintenance or location of the air input to the compressor. Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, flammable and highly toxic gas. ... Lubricants are an essential part of modern machinery. ... A Diving Air Compressor is a gas compressor, which can fill diving cylinders with high pressure air that is pure enough to be used as a breathing gas. ...

Poisonous additives can also get into the breathing mix if any material inside the blending valves or pipes burns, for instance when adiabatic heating occurs when decanting oxygen. This article covers adiabatic processes in thermodynamics. ...

Oxygen Precautions

In the presence of large volumes of high-pressure oxygen, one corner of Fire Triangle exists in good measure. It is vital the other two corners are not allowed to exist. The fire triangle. ...

Internally, the blending equipment and diving cylinders must be oxygen clean; all fuels and particles which could be sources of ignition must be removed. The materials chosen for use in the valves, joints and compressors must be oxygen compatible: they must not burn or degrade readily in high oxygen environments. Fuel is a material with one type of energy which can be transformed into another usable energy. ... Ignition occurs when the heat produced by a reaction becomes sufficient to sustain the reaction, whether it be a fire, an explosion, or nuclear fusion. ...

In gas blending, high temperatures are easily produced, by adiabatic heating, simply by decanting high-pressure gas into lower pressure pipes or cylinders. The pressure falls as the gas leaves the opened valve but then increases when the gas encounters obstructions such as a cylinder or a bend, constriction or particle in the pipe-work. This article covers adiabatic processes in thermodynamics. ...

One simple way to reduce the heat of decanting is to open valves slowly. With sensitive valves, such as needle valves, the gas can slowly be allowed through the valve so that the pressure increase is slow on the low pressure side. The pipe-work, joints and valves in the blending system should be designed to minimise sharp bends and sudden constrictions. Sometimes 360 degree loops are present in the pipe-work to reduce vibration. A needle valve is a type of valve usually used in flow metering applications. ... See Oscillator (disambiguation) for particular types of oscillation and oscillators. ...

Spaces where gas is blended or oxygen is stored should be well ventilated to avoid high concentrations of oxygen and the risk of fire.

Blending Nitrox

With nitrox there are several methods of gas mixing: Typical decal used on scuba cylinders containing Nitrox Nitrox is a breathing gas consisting of oxygen and nitrogen (similar to air), but with a higher proportion of oxygen than the normal 20. ...

• Mixing by partial pressure: a measured pressure of oxygen is decanted into the cylinder and cylinder is "topped up" with air from the diving air compressor
• Pre-mix decanting: the gas supplier provides large cylinders with popular mixes such as 32% and 36%
• Mixing by continuous blending: measured quantities of oxygen are introduced to the compressor inlet
• Mixing by density (weight): oxygen is added to a partially full cylinder that is accurately weighed until the required mix is achieved
• Mixing by gas separation: a nitrogen permeable membrane is used to remove smaller nitrogen molecules from the mix until the required mix is achieved

General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... A Diving Air Compressor is a gas compressor, which can fill diving cylinders with high pressure air that is pure enough to be used as a breathing gas. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ...

Blending helium mixes

With trimix, measured pressures of oxygen and helium are decanted into a cylinder, which is "topped up" with air from the diving gas compressor. Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used during the deep phase of dives carried out using Technical diving techniques. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...

With heliox, measured pressures of oxygen and helium are decanted into a cylinder. Heliox is a gas that is composed of a mixture of helium (He) and oxygen (O2). ...

With heliair, a measured pressure of helium is decanted into a cylinder, which is "topped up" with air from the diving gas compressor. Heliair is a breathing gas consisting of mixture of oxygen, nitrogen and helium and is often used during the deep phase of dives carried out using technical diving techniques. ...

A combined oxygen and helium gas analyser measuring a trimix fill

Image File history File linksMetadata Download high resolution version (1296x972, 206 KB) Summary An Analox combined oxygen and helium gas analyser being used to measure a trimix fill in a 3 litre cylinder Licensing I, the creator of this work, hereby release it into the public domain. ... Image File history File linksMetadata Download high resolution version (1296x972, 206 KB) Summary An Analox combined oxygen and helium gas analyser being used to measure a trimix fill in a 3 litre cylinder Licensing I, the creator of this work, hereby release it into the public domain. ...

Quantities and accuracy

To plan a dive to avoid oxygen toxicity and decompression sickness, the diver needs both specify the required mix for the gas blender to create and to check the proportions of oxygen and inert gases in the final mix before diving. Generally the tolerance of each final component gas fraction should be within +/-1% of the required fraction. Oxygen toxicity or oxygen toxicity syndrome is severe hyperoxia caused by breathing oxygen at elevated partial pressures. ... Decompression sickness (DCS), divers disease, the bends, or caisson disease is the name given to a variety of symptoms suffered by a person exposed to a reduction in the pressure surrounding their body. ...

Calculating composition

When blending mixes with pressures less than 250 bar / 3600 psi, the Ideal gas law holds and simple equations can be used to calculate the pressures of each component gas needed create the mix. Above this pressure, the composition of the final mix is difficult to predict using simple equations but needs the more complex Van der Waals equation. Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface. ... Isotherms of an ideal gas The ideal gas law is the equation of state of an ideal gas. ... The van der Waals equation is an equation of state for a fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle force (such as the van der Waals force. ...

Effects of adiabatic heating

Increases in temperature when filling make it difficult to accurately decant or pump a measured quantity of gas. When cylinders are filled with gas quickly, typically in 10 to 60 minutes at a dive filling station, the cylinder get hot, heating the gas inside, which increases the pressure of the gas. When the cylinder cools the gas pressure falls.

There are several solutions to this problem:

• fill the cylinder to the required pressure and let the cylinder cool, measure the pressure and then repeat the process until the correct pressure is achieved. The cooling interval needed depends on the ambient temperature.
• fill the cylinders in a water bath. The higher thermal conductivity of water than that of air means that heat in the cylinder is more quickly removed from the cylinder as it fills.
• fill the cylinders with 5 to 20% more gas than required. If the overfill is well judged, when the cylinder cools the final pressure will be with to the required pressure.

Gas analysis

Before a gas mix leaves the blending station and before the diver breathes from it, the fraction of oxygen in the mix should be checked. Usually electro-galvanic fuel cells are used to measure the oxygen fraction. Helium gas analysers also exist, although they are expensive at present, which allow the Trimix diver to find out the proportion of helium in the mix. An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ...