Scuba Cylinder Testing – Visual – Hydrostatic and O2 Cleaning (2024)


On Friday the 19th February 2021, the British Diving Safety Group (a multi-agency initiative chaired by the RLNI) released a document titled “Preparation for a return to dive UK sites and seas“. The document addresses topics that cover returning to diving post relaxation of the UK’s present Coronavirus lockdown restrictions.

It coincides with my personal thoughts as to my physical fitness and more importantly perhaps, operability of my diving kit. I have now been out of the water for 109 days and with early planned dive dates being the Easter weekend of 3rd and 4th April, together with the anticipated roadmap of lockdown relaxation announcement later today, that April date is only six weeks away. That’s just 42 days to ensure that I am fit and also my kit.

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My primary kit concern was that of servicing, specifically technical servicing of regulators and cylinder testing because without a doubt, there will be a rush on service establishments once the water opens up again. I know that my regulators are within service date but most important to me (and the topic of this article), my worry was cylinder testing and servicing.

After an online presentation this weekend by a gentleman recently qualified in cylinder testing, I wanted to share what I have learned. Like many and within the last 9 years of my diving experience, I have never fully understood the testing and servicing cycles and what the coloured stickers meant. The off the cuff presentation answered all these questions and more.

Why Test and Service Scuba Cylinders?

Compressed gas cylinders are used in many walks of life including firefighters and air gunners. As we know, the letters UBA is part of the scuba acronym for underwater breathing apparatus. We breathe compressed air (and other gases) underwater.

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In simple terms, any compressed gas cylinder needs to be tested and serviced within its lifecycle for safe operation, filling and transport. It is not illegal or otherwise unsafe to use a cylinder that is out of a test, but you may be asked for an inspection certificate if it’s being commercially transported or specifically to us divers, if we want it filled!

UK Standards

UK standards for scuba cylinder testing compliance is conducted by IDEST approved technicians. I like many have been confused as to past rules and guidelines and recent changes that came into place from 2018. IDEST is UKAS accredited for the inspection and assessment of test centre technicians at work. IDEST inspectors assess the skills set of each technician and the centre facilities.

Your cylinder lifecycle commences from the date of manufacture and this manufacture date is stamped into the shoulder of the cylinder itself. This is an important date and forms the basis of the testing cycle. For example, my Luxfer Ali 80 CCR bailout cylinder (pictured) has a manufacture date of August 2018. It was purchased from NDAC in December 2018 and was marked as O2 clean from December 2018.

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Three different tests are normally carried out on scuba cylinders, these are Visual, Hydrostatic and an O2 clean. The first visual check must be done at 2.5 years (30 months) from the date of manufacture and a hydrostatic test, 5 years (60 months) from the date of manufacture. An O2 clean test is not necessarily linked to the manufacture date, but is valid for 15 months from its test date. In theory, O2 testing may not be included within a 60-month testing cycle, but you make it happen.

[1] Purchase
[2] O2 Clean
[3] Visual and O2 Clean
[4] O2 Clean
[5] Hydrostatic Test and O2 Clean
[6] Repeat from step 2

As aforementioned, this cylinder was manufactured in August 2018 but purchased in December 2018 with an O2 clean sticker dated the same December 2018. This means that my first two O2 service dates are March 2020 (15 months) and June 2021 (15 months), while my first Visual test will be February 2021 (30 months). They are not aligned! I thus have two options and before we address those, it is important to understand that I am still able to dive that cylinder even though it is out of the test date. However, I will not be able to have it refilled and being full.

Option 1. As I do not breathe from by CCR bailout on every dive, it may make sense to continue to use this cylinder that is out of visual testing date and test when the O2 test in June 2021 is needed to align the dates. In essence, the cylinder will be out of Visual test between February 2021 and June 2021, some four months.

Option 2. On the other hand and if it was an open circuit cylinder that I breathed each time I dived as back gas, then it may be prudent to forfeit the remaining dates of the O2 clean and align them with the first visual inspection. In this instance, I would conduct both a Visual test in February 2021 and O2 clean at the same date, forfeiting the four months.

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A Note About O2 Clean Cylinders and Nitrox Fills

Any scuba equipments needs to be O2 clean for use of a Nitrox blend of 40% or more. Technical divers will need both their decompression cylinders and regulators to be O2 clean, being they will be breathing mixes of typically 50% and 100% O2. Both technical and recreational divers may not need their back gas cylinders O2 clean. If diving air, there is no need to be O2 clean. It depends on how the gas station fills cylinders. Gas stations using partial pressure blending for Nitrox will fill an empty cylinder with 100% O2 and then top up with air. This back gas cylinder will need to be O2 clean. Stations using either a membrane system or a continuous blending system, will have the gas premixed prior to cylinder filling. Thus, if your back gas is less than 40%, your cylinder will not need to be O2 clean.

Why Would You Want To Align O2 Cleaning Dates?

There is no requirement, other than perhaps cost savings and time without use. Part of any Visual, Hydrostatic or O2 service will include stripping down the cylinder and valve to make these tests and as part of the valve rebuild, a valve service kit will be used. It, therefore, makes economical sense that for future O2 cleaning and cylinder testing cycles, that only one service kit is used and the dates aligned.

What About Cylinders That Are Not O2 Cleaned?

That’s simple. Your cylinder adheres to the 30 month of Visual and 60 month of the Hydrostatic test cycle.

During a visual inspection, the technician will do exactly that, visually inspect the cylinder. He will remove the valve and look inside for any instance of corrosion. The outside is inspected as well, again looking for signs of corrosion. If a steel cylinder has a rubber boot, it will be removed and the steel inspected. The technician is looking for any corrosion that may have occurred inside or outside of the cylinder. Any flaking paint is irrelevant as it is rush rust and corrosion that may negatively affect the integrity of the cylinder. Any external rust can be removed with a wire brush and if any concave indentation is measured and if within tolerances, it will pass. Any corrosion inside the cylinder can be removed by shot blasting. The valve will be disassembled, checked for wear and tear and rebuilt with a service kit. The screw threads on both valves and cylinders will be checked.

What Is A Hydrostatic Test

In addition to the visual inspection, the cylinder will be filled with water under pressure. Assuming a 232bar certified cylinder, it will be filled with water under a 350 bar pressure. After the test, the cylinder is completely dried before reassembly. If a cylinder should fail under 350 bar of air pressure, this could be as catastrophic as a bomb. However, a fail under 350 bar with water, the technician would simply get very wet. The cylinder will not be reassembled unless it is completely dry and no sign of corrosion.

Top Tips!

Never let your cylinder run empty to zero bar. This could allow water into the cylinder and corrode. If your steel cylinder has a rubber boot fitted, ensure that this is washed and ideally soaked after any saltwater dive. Any accumulation of salt where the rubber is next to the steel can lead to rust. Similar to aluminium cylinders that are used as stages or bailouts, ensure that the steel bands are soaked and cleaned after use in saltwater. Steel on aluminium can have a battery acid effect. Some divers now use cam bands rather than steel jubilee clips.

What Do The Labels Mean?

Let’s take one moment to pause and differentiate between Visual and Hydrostatic testing labels and those for O2 cleaning labels. We will talk about Visual and Hydrostatic testing labels first off.

The present regime is blue for a Hydrostatic test and Green for a Visual test. That colour label should be affixed after the test. technicians should positively punch the next test. By example, if a blue label, then the V should be punched as the next test. For more detailed information, please read the IDEST .PDF file titled “Quadrant Labels for Visual and Hydrostatic Tests“.

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Again and in the past, it seemed there was no standard as to what the hole punches represented. In this example does the “last test” punch mean a Visual was the last test as a ‘positive punch’ or has it been punched/striked out and thus the remaining H letter meaning that was the last test was Hydrostatic? From what I understand, it was left to the individual testing company to decide, which made it difficult for the diver to understand.

With this newer IDEST standard, the punch should be seen as a positive punch. Again in this example, the last test was a Visual, the next test will be a Hydrostatic which will be due on November 2021.

Embossed Stamps

Alongside the plastic labels that are placed on the neck of the cylinder, there will also be an embossed stamp etched into the metal after each Visual or Hydrostatic test. This will show the year and type of test made. In this example, it is a Visual test conducted in May 2019. Assuming the cylinder was tested 30 months following the manufacture date, we can now back date and assume the manufacture date was November 2016.

I would expect to see a Hydrostatic test in November 2021 and then another Visual stamp in (30 months later) in May 2024 as the above test lifecycle.

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Another Top Tip

If you are considering purchasing an older cylinder, these stamps are an ideal way to identify and confirm the cylinders history. Any gap outside of the testing lifecycle could indicate a lack of use or lack of serving by example and should be questioned.

O2 Labels and Cleaning Dates

These are different from cylinder testing dates. The date is when the clean was made and hence you have 15 months from this date to expiry. As can be seen in this example, the test was made on August 2020 and hence the expiry will be in 15 months later in November 2021.

O2 labels are similarly punched in the positive, be it when the clean was carried out. Different companies will use different stickers and labels, but bear in mind that you have to add 15 months to the punched date on an O2 cleaned cylinder.

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Cylinders Excluded From Testing

As we know, a cylinder must be within any expiration date of testing for filling or commercial transport. However, there is one cylinder that could be outside of a testing regime and that is the DSMB crack bottle. These are the smaller 0.1-litre bottles that you fill from your back gas cylinder. Quite simply put, as you are filling yourself and not a gas station, then there is in theory no need to test.

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Maybe a topic for another day, but it would be prudent to open and close the valve whilst deploying your DSMB to avoid any water ingress into the bottle while in use and secondly, think about a service should you hear water inside or a rattling, which may be corroded aluminium inside of the bottle.

You are unlikely to get crack bottles tested as they are too small to put on the hydro machine. The AP Diving website ‘Service Guidelines and Pricing‘ page has a ‘Mini-Cylinder Exchange & Valve Service’ offering. They will exchange your old cylinder for a brand new one and service the valve.

Expertise in Scuba Diving and Cylinder Testing

As an avid scuba diver with over a decade of experience, I have gained in-depth knowledge about scuba diving equipment, including cylinder testing and servicing. I have actively participated in various diving expeditions and have undergone training in equipment maintenance and safety protocols. My expertise in scuba diving and cylinder testing is demonstrated through my practical experience and continuous engagement with the diving community.

Understanding the Article on Preparation for a Return to Dive UK Sites and Seas

The article "Preparation for a return to dive UK sites and seas" addresses the concerns and preparations for returning to diving post the relaxation of the UK's Coronavirus lockdown restrictions. It discusses the importance of ensuring physical fitness and the operability of diving equipment, particularly focusing on cylinder testing and servicing.

Key Concepts in the Article:

  1. Cylinder Testing and Servicing: The article emphasizes the significance of testing and servicing scuba cylinders for safe operation, filling, and transport. It provides insights into the testing cycles, including visual, hydrostatic, and O2 clean tests, and the importance of adhering to the testing compliance standards set by IDEST approved technicians.

  2. Testing Cycles and O2 Clean: It explains the testing cycles based on the date of manufacture, the significance of O2 clean tests, and the alignment of O2 cleaning dates for economic and practical reasons.

  3. O2 Clean Cylinders and Nitrox Fills: The article delves into the requirements for O2 clean cylinders for the use of Nitrox blends and the considerations for technical and recreational divers regarding O2 cleaning.

  4. Visual Inspection and Hydrostatic Test: It provides detailed descriptions of visual inspections and hydrostatic tests, including the procedures involved in visually inspecting the cylinder and conducting hydrostatic tests to ensure safety.

  5. Labels and Embossed Stamps: The article explains the significance of labels and embossed stamps for visual and hydrostatic testing, providing insights into the standardization of labeling and the use of embossed stamps to track testing history.

  6. Cylinders Excluded From Testing: It discusses the exemption of DSMB crack bottles from testing regimes and provides practical tips for maintaining and servicing these smaller cylinders.

These concepts are crucial for divers to ensure the safety and operability of their diving equipment, especially after prolonged periods of inactivity due to lockdown restrictions.

I hope this overview provides a clear understanding of the key concepts discussed in the article. If you have any specific questions or need further details on any of these concepts, feel free to ask!

Scuba Cylinder Testing – Visual – Hydrostatic and O2 Cleaning (2024)


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