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Cylinder Testing

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Cylinder Testing

As the new diving season is approaching it is important that the maintenance of your scuba equipment is up-to-date and you ensure anything outstanding is dealt with. Your diving cylinder is an essential piece of diving equipment but is often overlooked. Statutory Regulations require scuba diving cylinders are tested regularly at defined intervals. Not following these regulations is a threat not just to your ability to dive, as refills will be refused by air fill centres, but also to your safety and the safety of those filling your cylinder. Cylinders out of test should not be used.

Cylinders require inspection at least every 2.5 years from the date of manufacturing or from the previous baseline date stamped on the cylinder. Every 5 years the cylinder needs to be hydrostatically tested (pressure tested) to make sure they are fit for purpose. Each time a hydrostatic / hydraulic test takes place the shoulder of the cylinder will be metal stamped by the test house with a new baseline date.

Cylinders should be inspected before each dive for any damage or anomalies.

Periodic Inspection and test (PIAT)

By statute all cylinders are metal stamped on the cylinder shoulder on manufacture and after each successful five year Hydrostatic Test. These are baseline dates. The stamp will consist of the test centre mark along with the YEAR and the MONTH that the test was done.  The blue quadrant label, used by IDEST Test Centres, will also be put on the cylinder shoulder near the metal stamping as a visual reminder by which time a future test is required and a paper test certificate will be issued.  The label will show an ‘H’ on the left-hand side to indicate a hydraulic test has been conducted.   On the right-hand side a letter ‘V’ will be readable as a visual reminder that the next visit will involve a visual inspection.  IDEST labels are made from a ‘tamper-evident’ material and any attempt to remove the label will result in the label breaking up into small pieces.  If a label is lost or damaged the advice is to return to the test centre and get a replacement fitted or have the test certificate handy to show a centre filler.

Hydrostatic / Hydraulic – five year cylinder tests
A hydrostatic test involves a visual and full pressure test. The cylinder is pressurised with water to its test pressure and measuring its volume before and after the test. Water, which is almost incompressible, is added to the cylinder creating pressure in the bottle and is raised to the test pressure which will be well above the operating pressure of your scuba tank. To measure the change in volume, the whole cylinder is immersed in a test chamber which is also filled with water. This chamber’s water volume is measured with a burette which will show any increase in the cylinder’s volume by forcing more water out of the chamber. An increase above the tolerated level means the cylinder will not pass the test and is permanently disabled from further use.

Visual – 30 month intermediate cylinder tests
To remain operable each cylinder requires a visual test to be carried at least evert two and a half years (30 months), depending on a risk assessment or diving regime, after the hydrostatic test has taken place. More frequent visual tests can be carried out.  If a cylinder is not tested within eighteen months of a visual test being required ie four years after a hydrostatic test a new full hydrostatic test will be required.  Prior to the visual inspection the cylinder is checked for an illegible, incorrect, or unauthorised permanent metal stamp marking which is always the baseline for any testing required. The procedure for conducting a visual inspection starts with the removal of the cylinder valve. Subsequently the cylinder undergoes an external visual inspection for damage such as dents, cracks, gouges, cuts, bulges, lamination, and excessive wear. When any damage is found it will be evaluated against rejection criteria. The internal visual inspection follows a similar process and is performed using a mirror and illumination to identify damage or defects. The valve and thread of the neck of the cylinder are also inspected for damage or defects. The valve will be stripped down, cleaned, worn parts will be replaced and it is then re-assembled. After the cylinder has passed the visual inspection a new IDEST label will be placed on the cylinder shoulder to indicate a visual test has taken place.  The label will show a letter ‘V’ on the left side indicating a visual test has taken place. On the right side a letter ‘H’ will be readable as a visual reminder that the next visit will involve a hydrostatic test. Significant corrosion of the cylinder inside or out can lead to the cylinder being permanently disabled from further use.

Oxygen Cleaning
Cylinder servicing can also include Oxygen cleaning for diving on Nitrox and other oxygen enriched gases. Cleaning ensures the correct greases and cleaning techniques are employed that make oxygen enriched gases safe to use. The tank will also be marked as O2 cleaned so gas filling stations know. Cylinders should be marked to show they are in oxygen service and require re-inspection / certification every 15 months.


The better the maintenance the longer your equipment will last . Good maintenance after every drive should be normal practice. Cleaning your cylinder with fresh water and leaving it to dry is as important as safe storage. Unfortunately this is often neglected and corrosion can set in.  When storing your cylinders you should maintain a slight positive pressure of at least 20 Bar in them. Holding this pressure prevents moist air entering and causing internal corrosion. Cylinders either standing up-right or in a rack. Never store the cylinder on bare concrete or any surface that may hold moisture or scrape and degrade the surface.




Regulators should be serviced in line with the manufacturers’ recommendations, which is commonly annually. In addition, any abnormality or fault should be checked out by a qualified service technician.

Before each dive check you can breathe through both regulator and octopus easily and that when the cylinder is turned off and after breathing down the regulator you are not able to breathe.  If you are able to breath the exhale valve(s) are worn and need replacing

All hoses should be checked before each dive for any signs of damage, abrasion or splitting. Likewise, all connections should be checked for leakage.


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