Appendix 2 | Some Parts & Pieces

I have intentionally shied away from providing very specific component specifications throughout this content since the fundamental principles and design theory can be applied with anyone’s favorite flavor of parts. However, I do think it’s valuable to present a few parts and pieces that seem to surface through numerous rebreather home build, maintenance, and modification projects, particularly when assembling hoses or other plumbing.

The following is some must-have information that may provide a useful reference someday.

Fittings

An entire manuscript could be compiled on the subject of fittings alone. For discussion here, I am presenting just a very small few of the more commonly encountered threads within dive systems. Interestingly, with exhaustive research into the topic, one will discover that most fittings used in diving have been borrowed from the automotive, medical, aviation, and welding industries.

Browse our comprehensive collection of fittings and adapters.

Today, adapters for just about every combination of thread to thread can be sourced. For those who frequently build their own hoses or makeup more comprehensive save-a-dive kits, the following chart are a few key threads to recognize and have on hand.

I use oxygen fittings very routinely in my diving equipment. They are easy to source, inexpensive, and very commonly used in commercial diving. Both barbed ends and threaded ends make it possible to make-up custom hose assemblies very quickly and with only a few parts.

Browse our selection of oxygen fittings.                  

Glands & Penetrators

Glands are often used to pass cables through the rebreather head and into the ambient pressure space of the rebreather. This pass through allows wiring to oxygen cells or other sensors. Glands do not need to be incredibly pressure tolerant since they simply create a watertight seal at ambient pressure. Glands will compression fit against the cable’s jacket to create this seal. The threaded end of the gland is often a standard pipe thread, which can be sealed with Teflon tape or a small amount of RTV sealant.

Threads commonly found in cable glands for rebreather apparatus include:

• 1/4 NPT
• 3/8 NPT
• PG7
• PG9
• M12x1.5

Some systems are beginning to evolve to embrace glands and threads more commonplace in subsea robotics. These include:

• M10x1.5
• 7/16-20 UNF

We are in the process of migrating to M10x1.5 penetrators throughout our rebreather and other electronic assemblies. These are becoming the standard within other subsea electronics and are purpose built for underwater applications. View options here.

Hoses

For rebreather gas supplies, I typically use hose that is overrated for its intended working pressure by at least double. This mitigates the minimal risk of blowing a hose and instills some confidence without having to move towards rigid stainless-steel tubing. On the ambient pressure feed side, nearly any hose will do, though I typically use the same hose as the supply side since it’s convenient and visually consistent.

Most standard scuba hoses have an inside diameter of ¼”. Hoses with ‘higher flow’ may be 5/16” inside diameter. In commercial diving, umbilicals are often 3/8” inside diameter. Always use the proper barb for the given hose. Metric equivalents for either hose or fittings are typically suitable. The ID for most barbed fittings common in SCUBA is 5mm. Smaller than that will restrict flow and potentially cause issues with adequate breathing gas volumes on demand. Larger than that is always airing on the side of conservatism.

Making your own hose in a pinch can be done with small pinch clamps. Match the clamps ID with the hose OD and you are in business. This is very simple, and reliable, and a great set of tools and supplies to have in a save-a-dive kit. Custom hose lengths can always be made up by a hose supplier, or one can invest in swaging tools, though I’ve found the little pinch clamps to be reliable and are my go-to for custom hose assemblies. For high pressure hose, I typically use two clamps per hose fitting for peace of mind, and this is a regulatory requirement for commercial diving umbillicals.