Filling Scuba Cylinders/Glossary

Definitions given here are in layman’s terms and should not be considered legally binding. Meanings given are in context of breathing air compression and there may be alternative meanings not mentioned here.

A

• AA6061: Aluminium Alloy 6061 (not subject to sustained load cracking)
• AA6351: Aluminium Alloy 6351 (subject to sustained load cracking – requires eddy current testing)
• A-clamp fitting/valve: See Yoke fitting/valve
• A-clamp adaptor: see Yoke adaptor
• activated charcoal/carbon: A filter medium
• air comprimé: Compressed air (French)
• aire comprimido: Compressed air (Spanish)
• ambient pressure: Pressure of the surroundings
• aria appiattita: Compressed air (Italian)
• assessment: Process by which knowledge and skills or observable conditions are compared to a standard before making a decision.

B

• block adaptor: Screw-in adaptor fitting which is fitted to a 200/240 bar DIN pillar valve to allow connection of a yoke regulator or filling whip
• booster: Machine used to increase pressure of a gas. Usually refers to case where inlet pressure is above ambient pressure already. (see also compressor)

C

• cascade filling: Decanting from several cylinders in succession, generally using a procedure to maximise charge pressures.
• charging pressure: Pressure stamped on a container for a permanent gas to indicate the maximum gauge pressure (measured or corrected to 15ºC) that may be applied at the time of filling
• commercial diving: Working under pressure: Occupational activity where gas is breathed at pressure in excess of atmospheric pressure
• competent person: Person who is able to perform a task or operation safely and according to required procedures. May require formal assessment or accreditation, or registration with government body.
• compressed air: Air at a pressure greater than ambient.
• compressor: Machine which pressurises gas. Generally intake gas is at ambient pressure, outlet gas at higher pressure. High pressure breathing air compressor output pressure is usually 200 to 330 bar
• compressor log: Book or file containing records of compressor operation, filling of cylinders and maintenance records
• compressor operator: Person who operates a compressor
• condensate: Liquid resulting from phase change from gas due to cooling or pressure change.
• cylinder: 1. (SANS 10019) Refillable container of water capacity between 0,5 L and 150 L. 2. That part of a reciprocating compressor or booster in which the piston is moved to compress the air. The internal space is cylindrical with a circular section. The external surface is usually finned for air cooling
• cylinder valve: Valve fitted to compressed gas cylinder to control gas flow into and out of the cylinder. Also Pillar valve
• Cyrillic markings: Markings in the Cyrillic alphabet, used by Russian and several other eastern European languages. Some typical examples of Russian language Cyrillic markings that a compressor operator is likely to encounter on compressed gas cylinders for diving:

Кислород (Keeslorod) Oxygen

Воздуха (Vozdoocha) Air

Нитрокс (Neetroks) Nitrox

Гелий (Geleey) Helium

Азот (Ahzot) Nitrogen

D

• decant: Transfer gas between cylinders by differential pressure. No energy is input, flow will stop when pressures equalised.
• DIN fitting/valve/thread: Usually refers to G5/8” x 14 parallel thread fittings used to connect cylinder valve to filling connection or regulator first stage. Available in 200 bar and 300 bar versions which should only be inter-connectable in safe combinations, but are sometimes modified. More reliable than the alternative Yoke connector.
• DIN plug: Screw in adaptor which can be used with many recent 200/240 bar DIN pillar valves to allow connection of Yoke regulators or filling whips.
• Druckluft: Compressed Air (German)
• Dräger (Draeger) tube: Indicator tube used for testing air quality

E

• eddy current test: Use of electromagnetic induction to detect flaws in conductive materials. It is used to detect cracks in parallel neck threads of aluminium cylinders. Also called Visual Plus inspection. Required for cylinders of AA6351 alloy

F

• fatigue cracking: Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.
• filtration: Process for removing impurities from a fluid. Particulates are commonly removed by passing the fluid through porous material with pore size small enough to trap the particles (e.g. micron filters). Liquids and gases are commonly absorbed or adsorbed by the surface of the filter medium (Activated carbon, Molecular sieve, Silica gel), or may be chemically combined with the medium (Sodalime) or catalytically converted (Hopcalite) into a less objectionable substance

G

• gaseous impurities: Contaminants in the compressed breathing air or gas mixture which are in gaseous form. Compare with particulate and condensate impurities.

H

• H-valve: Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
• heliox: Mixture of helium and oxygen for use as a breathing gas
• hopcalite: Catalyst sometimes used in air filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide
• hydrostatic test: Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (qv) and measured for permanent set.
• hyperfilter: Additional filter to produce air of oxygen compatible quality. This may be built into the filling system or temporarily connected when required.

I

• internal condition of cylinder: The state of the internal surface of a cylinder regarding corrosion, contamination and cracking.

J

• J-valve: Scuba cylinder valve with lever operated reserve mechanism
• J-cylinder: Bulk gas storage cylinder with internal volume ????

K

• K-valve: Scuba cylinder valve without reserve mechanism

L

• learning outcomes: The demonstrable abilities of the learner who may be assessed as competent in terms of the training standard. These include Skills, Knowledge and Attitudes, though attitudes may be difficult to validate.
• lubrication: Use of a third substance to reduce friction and wear between two surfaces where there is sliding relative motion. Commonly oils and greases are used for this purpose.

M

• manufacturing standard/code: Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.
• molecular sieve: Material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level.
• multiple stage compressor: Compressor in which gases are compressed more than once, often with cooling between stages. Used to improve efficiency and reduce temperatures.

N

• nitrox: Mixture of nitrogen and oxygen for use as breathing gas. Usually with oxygen percentage higher than air. Also called “Enriched Air Nitrox” (EAN)

O

• OHS Act: South African Occupational Health and Safety Act, 1993 (Act No 85 of 1993)
• outcomes: see Learning Outcomes
• ossigeno: Oxygen (Italian)
• oxígeno: Oxygen (Spanish)
• oxygen clean: Cleaned for oxygen service by appropriate methods and materials and tested for contaminants.
• oxygen compatible: Made from materials which are suitable for oxygen service.
• oxygen compatible air: Air which has been filtered to reduce contaminants to a level suitable for blending with high pressure oxygen.

P

• personal safety equipment: Equipment worn by personnel to reduce risk of injury at sites where it is not practicable to eliminate the hazard, including ear protectors, safety glasses, hard hats, gloves, overalls, respirators etc
• pillar valve: see Cylinder valve
• positive displacement: (of compressor) Compresses gas by reducing volume of compression chamber (cylinder) by mechanical means (piston) to produce higher pressure of the contents.
• pre-fill external inspection: Examination of the external condition of a pressure vessel and fittings to ensure that it complies with requirements before accepting for filling.
• presión de carga: Charging pressure (Spanish)
• pression de remplissage: Charging pressure (French)
• Pressluft: Compressed Air (German)

R

• RPL: Recognition of Prior Learning: Principle which recognises that learning of a skill can occur by non-formal means, and provides methods for formal recognition of those skills.
• reciprocating compressor: Compressor in which the volume of the compression chamber/s is cyclically changed by reversing linear motion. Eg: a piston moving back and forth in a cylinder.
• reject criteria: Features, states or conditions which are not acceptable.
• residual gas: Gas remaining in cylinder from previous fill.
• residual pressure: Pressure of gas in cylinder from previous fill.
• Russian terms: see Cyrillic markings

S

• SCBA: Self Contained Breathing Apparatus (not for underwater use)
• SCUBA or scuba: Self Contained Underwater Breathing Apparatus
• SSDE: Surface Supply Diving Equipment
• separator: Device which facilitates the separation of liquid particles from the compressed gas, usually with a drain to periodically remove accumulated liquid from the system.
• serial number: Number stamped on the cylinder by the manufacturer in the shoulder area which identifies the cylinder. In combination with the manufacturer’s identification this will be unique to the cylinder.
• silica gel: A desiccant filter medium used to adsorb water.
• sintered: Partiulate or granular material bonded together by the application of pressure and sufficient heat to partially melt the surface of the particles and weld them together. The product is usually porous.
• slingshot valve: see Y-valve
• standard operating procedure: Procedure compiled by an organisation prescribing the processes to be followed when performing specified tasks.
• sustained load cracking: The development of cracks in a material subjected over long term to static stress significantly less than the yield stress. There is a significant risk of this mode of failure in pressure vessels of AA6351 alloy

T

• test pressure: Pressure at which the cylinder will be hydrostatically tested for revalidation
• top up: To reconnect a cylinder where the charge pressure is lower than the acceptable limit and add gas until the pressure is sufficient
• Trade Metrology Act: South African Government Act no. 77 of 1973. To consolidate and amend the law (of South Africa) relating to trade metrology (measurement)
• trimix: Mixture of three gases for breathing. Oxygen, Nitrogen and Helium are the gases used. The gas fractions will usually be specified.

V

• visual Inspection: Internal and external inspection of a pressure vessel as part of revalidation procedure.
• Visual Plus: Eddy current test (q.v.) of parallel neck threads of aluminium cylinders.

W

• water capacity: Of a cylinder: The internal volume. The amount of water it would hold at ambient pressure at 20°C
• water trap: Mechanism to trap liquid water carried by the compressed gas
• working pressure: Maximum filling pressure rating for the cylinder at standard temperature. (also Charging pressure)

Y

• Y-valve: Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to H-valve but in Y configuration. Also known as Slingshot valve.