FAQ ABOUT HARDWARE AND SOFTGOODS
There is no reliable visual inspection method to determine O-ring material composition, only specialized materials testing equipment can make that determination. Acrylonitrile butadiene rubber elastomers (aka NBR, aka Nitrile, aka Buna-N) are considered to have good resistance to oxygen with a 15 year shelf life. Fluorocarbon elastomers (aka FKM, aka FPM, aka Viton) are considered to have excellent resistance to oxygen, with an essentially unlimited shelf life. To ensure specific composition, O-ring material must be specified at time of purchase and then segregated from other O-rings.
There are no O-ring color coding standards and thus color or appearance is not an indication of the material or quality. O-rings are available in nearly any color, although most commonly seen in black regardless of material. Even though most fluorocarbon O-rings are black, the loose FKM O-rings sold by Dive Gear Express are oxygen compatible and usually brown or green; simply to make them easily distinguishable from more common NBR O-rings which are usually black. However, O-rings inside equipment (valves, regulators, hoses, service kits, etc.) are almost always black regardless of material. O-ring materials also can not be distinguished from each other by their surface appearance, more a function of the manufacturer than the material. NBR is incorrectly said to have a shiny surface and FKM a matte surface. This is not a reliable indicator, and certainly not true if the O-ring has been lubricated.
Just to be clear, the COLOR and SURFACE APPEARANCE of the O-ring is MEANINGLESS regarding their compatibility with oxygen.
Yes. Many divers are surprised to learn the SCUBA industry convention of using fluorocarbon elastomers (FKM or FPM, aka Viton o-rings) with Nitrox is not a matter of oxygen fire safety. The introduction of Nitrox in recreational diving included a recommendation to use FKM for seals in gas blending equipment whose wetted surfaces contact pure Oxygen. This was frequently confused with the very important safety requirement for oxygen cleanliness (i.e. the absence of readily combustible materials); creating a mistaken but widely held belief that Viton is also somehow related to safety of Nitrox for diving equipment such as SCUBA regulators and cylinder valves.
FKM is no more 'safe' in Nitrox diving applications than ordinary synthetic nitrile rubber (NBR aka Buna-N). While FKM has a slightly higher temperature of ignition at {~ 900°F | 500°C} than NBR at {~ 750°F | 400°C}, nearly any material can still serve as fuel in the kindling chain to an oxygen fire that will reach {~ 5000°F | 2700°C}. The reason for preferring FKM in high oxygen content applications is because the service life is typically longer than NBR, i.e. Viton is more resistant to oxidation than nitrile rubber although FKM also exhibits a tendency to swell slightly in high-pressure oxygen. While FKM o-rings theoretically outperform NBR o-rings, in practice there is no safety reason to prefer them in Nitrox SCUBA life-support applications such as regulators and valves given the periodic service requirements of such equipment.
Regardless, Dive Gear Express specifies oxygen compatible and oxygen clean products whenever possible, and we only use viton O-rings and O2 compatible lubricants in equipment service. Any products we identify as Nitrox Ready or Oxygen Service will meet industry standards for both oxygen compatibility and oxygen cleanliness prior to initial use.
The short answer is NO. The longer answer is it depends on the exact product formulation and gas pressure but as a practical matter the answer is still no. Silicone "grease" is a generic term for a variety of lubricant formulations that are based on some form of pure silicone oil, most commonly polydimethylsiloxane (PDMS). While pure PDMS itself is a chemically inert inorganic substance that is not combustible; in order to make the little tub or spray can of generic 'scuba lube', the PDMS is mixed with thickeners and/or organic solvents that typically are readily combustible. Lubricant contamination in high pressure compressed gas equipment is a frequent cause of oxygen fires. In general, lubrication in oxygen service applications should be avoided whenever possible. Oxygen service applications in SCUBA that require lubrication must use specialized (and relatively expensive) lubricants, typically based on polytetrafluoroethylene (PTFE) or polychlorotrifluoroethylene (PCTFE) compounds.
It is true that in low pressure Nitrox applications such as regulator second stages and rebreather loops, the type of lubricant is pretty much irrelevant to oxygen fire safety. Occasionally, the desire to minimize use of expensive oxygen compatible lubricants can lead to the erroneous assumption that inexpensive silicone lubricants might used in ambient or low pressure applications that are in close proximity to high pressure applications. However, the high tack and adhesion property of silicone lubes also makes them very migratory and difficult to completely remove. In practice, we find silicone lubrication on the low pressure side of equipment will eventually be transferred to the high pressure side such as a first stage connector or valve outlet. Never use silicone lubricants with electrical contacts, even though this is an often suggested practice. Silicone products will react with plastics and other contaminates to form insulating films and silicone carbide compounds which can cause intermittent connections in low-current applications such as rebreather oxygen sensors. When multiple lubricants are available, there is also the very real increased risk of inadvertently applying the wrong lubricant. In practice, if lubrication is required it is best to only use oxygen compatible lubricant consistently throughout all equipment in service with Nitrox regardless of pressure.
Dive Gear Express avoids silicone lubricants in our facility, using only oxygen compatible lubricants for all SCUBA applications that require lubrication. Any products we identify as Nitrox Ready or Oxygen Service will meet industry standards for both oxygen compatibility and oxygen cleanliness prior to initial use.
Yes. Shock cord, surgical tubing, and nylon webbing are all priced and ordered in units of {1 ft | 30 cm}, but we would look pretty foolish if we actually shipped it in little pieces. Orders of cord and webbing up to {50 ft | 15 m} are shipped as one continuous piece. Surgical tubing is different; tubing orders up to {10 ft | 3 m} are shipped as one continuous piece. For example, if you want a continuous length of ten feet or three meters, order ten units.
If you need a large amount of the cord or tubing, we also sell it in bulk rolls at a better price.
Unfortunately, there is no meaningful number we can use to describe the stiffness of our DGX Gears {2 in | 5 cm} harness webbing. The best answer we can give is that our webbing is what we believe to be the "correct amount" of compromise between flexibility and stiffness for the specific application of SCUBA diving BCD harnesses - stiffer than "seat-belt" webbing but less stiff than "tank-strap" webbing. The webbing may seem a little too stiff at first, but once wet and "broken-in" it will be the correct amount of stiffness to hold a shape and be comfortable.
Assembly screws are also called "book screws" or "sex bolts", and are available in both metal and plastic versions. Years ago our suppliers used to include a metal set with their wings and later switched to a plastic set, but have not included either for a long time because assembly screws are often counterproductive.
The plastic assembly screws can be used to attach the wing directly to a hard metal backplate when rigged for a single tank without a single tank adapter. Note that this function is just cosmetic, omitting the assembly screws does not cause a problem. Without the assembly screws, when the BCD is taken off a single tank, the wing will hang loose on the cam straps.
The metal assembly screws can be used to attach accessories to the holes on edges of metal backplates, but in our opinion the plastic ones actually work better. Don't be concerned about the strength of plastic vs metal; the plastic version is plenty strong for these applications plus they are not subject to galvanic action and don't cause wear on materials rubbing against them.