Scuba cylinders that are used for Nitrox/Trimix must be specially cleaned for use with oxygen. This is because nitrox mixes are typically prepared by emptying the cylinder first, then adding 100% oxygen to the required amount before topping up with air to get the right mix. Oxygen cleaning must be carried out every 18 months due to the risk of contamination. In order for a cylinder to be filled with Nitrox / Trimix it must have a valid oxygen test label. If this is not present, or it is out of date, then the cylinder will not be filled with Nitrox/Trimix.
During the oxygen cleaning process, the cylinder is washed, cleaned to remove all traces of hydrocarbons, and the valve refitted with oxygen compatible (viton) o-rings.
Why must high-pressure cylinders be tested? All high pressure cylinders with an internal volume greater than 0.5 litres must be hydrostatically tested every 5 years from the date of manufacture (stamped on the cylinder) to ensure that the cylinder is structurally sound.
What is a hydrotstaic test?
A hydrostatic test is an approved way to test the structural integrity of a high-pressure compressed gas cylinderIt is carried out by removing the valve, filling the container with water, and then pressurising the cylinder above its operating limit. The expansionof the cylinderis measured, recorded, and analyzed. All high pressure cylinders with an internal volume greater than 0.5 litres must be hydrostatically tested every 5 years.
Why do air gun cylinders only need testing every 5 years?
Cylinders not used for scuba diving that have a special surface valve fitted, only require hydrostatic tresting every 5 years. This is because there is little risk of water entering the cylinder.
Why do scuba cylinders require testing every 30 months? Cylinders used for scuba diving must be tested every 30 months due to the risk of water getting inside the cylinder. The test will either be a visual test with valve service, or a hydrostatic test with valve service. Hydrostatic tests must be carried out every 5 years.
Why must cylinders be cleaned for Nitrox/Trimix?
Scuba cylinders that are used for Nitrox/Trimix must be specially cleaned for use with oxygen. This is because nitrox mixes are typically prepared by emptying the cylinder first, then adding 100% oxygen to the required amount before topping up with air to get the right mix. Oxygen cleaning must be carried out every 18 months due to the risk of contamination.
Why might a cylinder require an internal shot blast?
It is possible that steel cylinders may accumulate rust on the internal surface of the cylinder. This could be due to water getting into the cylinder or from air fills that contain hugh levels of moisture. Rust if severe can lead to weakening of the cylinder wall and therefore the cylinder being condemned. Small amounts of surface rust can removed through shot blasting the inside of the cylinder with particles.
