The Submersible Pressure Gauge
The Submersible Pressure Gauge is vital piece of equipment for every diver—functioning as a cylinder contents gauge, much like the fuel gauge of a car.
Most people learn to dive using a console containing an SPG, a compass and either a computer or depth gauge. Superficially, this seems like a good idea, keeping all those handy instruments in one place. However, there are some serious drawbacks to such an approach.
Multipurpose consoles are large and cumbersome, often dragging along the bottom or catching on coral or wrecks. In an overhead environment stirring up silt could be disasterous, reduced visibility leading to disorientation or worse. Ask yourself how often you have seen a console dragging along, impacting the environment and out of reach when needed.
The computer or depth gauge and compass are better positioned on the wrist where they are easily referenced without subsuming your entire focus and unable to impact anything—leaving only the SPG on a shorter, cleanly stowed high pressure hose.
SPGs are best made of brass and glass. Plastics are easily broken and scratches on a plastic facing can make the gauge difficult to read. On deep dives plastic can even flex inward causing the needle to stick and the gauge to read incorrectly. A brass and glass SPG withstands higher pressures at depth and gauges manufactured this way tend to be of a higher quality and more accurate.
High pressure hoses are usually around 36”/92cm, an excessive length that bows out from the body, causing additional drag and potentially snagging. Ideally, a high pressure hose should be 24”/61cm and clipped off to the left hip using a stainless steel bolt snap. Stowed this way the SPG and hose are streamlined and protected. Like anything, practice is needed to become proficient at quickly unclipping and reclipping the SPG when referencing it.
The bolt snap should be fastened to the SPG with cave line, allowing it to be cut away in the unlikely event the bolt snap jams. Using cave line instead of o-rings or zip ties is far less prone to unexpected breaks.
The connection between the SPG and high pressure hose contains a tiny swivel pin sealed by two tiny o-rings. These o-rings wear over time and the degradation is accelerated by salt, grit and sand. Consequently, you should keep your SPG clipped off and out of harms way when not reading it. With the SPG safely stowed, we also no longer need a rubber boot protecting it. These boots seem like a good idea initially, but actually trap salt, grit and sand, simultaneously degrading the swivel pin o-rings, while hiding any damage and potential leaks.
Configuring your SPG this way simplifies your equipment, makes deploying and referencing the gauge clean and easy and keeps the SPG safely tucked away, minimising drag and damage to both it and the environment—all contributing to a more pleasant, comfortable and safe diving experience.