By Mario Medarevic
Published on DiveWorld.ca
The submersible pressure gauge—commonly known as the SPG—is one of the most fundamental components in a diver’s gear setup. Despite its simple, analog design, it’s often misunderstood. In an age where digital dive computers and wireless transmitters dominate the conversation, it’s easy to overlook the value of this compact device.
Let’s clear up some common misconceptions about SPGs and explore why they still play an essential role in safe, informed diving.
Nearly all SPGs feature a red section below 50 bar, which many divers interpret as a reserve indicator—similar to a fuel warning light in a car.
But that’s not what it means.
The red zone isn’t a countdown to empty. It’s a manufacturer-issued caution that readings below 50 bar may be less accurate due to the gauge’s internal mechanics. It’s not a safety threshold, nor does it reflect the volume of gas remaining.
Here’s the nuance:
50 bar in a small single tank contains far less usable gas than 50 bar in twin cylinders
While the pressure is the same, the total gas volume differs drastically
Some dive operators still require divers to surface with at least 50 bar, which is a fair safety margin—but interpreting the red zone as a “reserve” can lead to misunderstandings. It’s there for accuracy, not urgency.
It’s true that wireless air integration has brought convenience and innovation to modern dive computers. But does that mean SPGs are outdated?
Not at all.
Analog SPGs offer advantages that digital devices can’t fully replace:
They provide mechanical feedback—a worn needle or sluggish movement can indicate issues like internal wear or blockage
They don’t rely on batteries, signals, or software
They’re rugged, dependable, and simple to maintain
Unlike most other hoses in a regulator system, the high-pressure SPG hose has no relief path. If water enters the first stage and travels into the SPG, it can accumulate, leading to corrosion or debris buildup. An experienced diver can often identify these problems just by observing how the SPG behaves during pressurization or purging.
In short, SPGs don’t just give you numbers—they give you insight into your system’s health.
There’s a widely repeated tip among divers to “turn the SPG away from your face” when opening a tank, in case the glass explodes.
Let’s debunk that.
SPGs operate under high pressure, yes—but they are low-flow devices. The internal orifice that allows pressure through the hose is extremely small, meaning that even in a rare failure, the pressure is released gradually, not explosively.
Tests and demonstrations consistently show that even damaged SPGs depressurize in a slow, controlled manner. They’re designed to withstand pressure safely, and the risk of injury is extremely low.
An SPG isn’t your dive computer—and it’s not your primary planning tool. Its job is to confirm that your gas usage matches what you’ve already planned.
Smart divers estimate their gas consumption in advance using known variables like:
Surface consumption rate (SCR) in liters per minute
Tank volume to convert liters into bar per minute
Dive depth, to calculate gas use under pressure
This proactive approach helps you anticipate gas use and recognize inconsistencies. Rather than reacting to SPG readings mid-dive, you check whether the reading aligns with your expectations. It’s also the best way to catch a faulty gauge early.
In poor visibility, digital displays can become hard to read. But an analog SPG, with its high-contrast dial and simple needle, offers clear, instant visual feedback—even when conditions aren’t ideal.
You don’t need a stack of backup gauges. A single, well-maintained SPG is more than enough—because it’s not about the gear making decisions. It’s about you making informed choices, with the SPG there to validate your plan.
In an emergency, like air sharing, an SPG is universally understood. There’s no need to interpret someone else’s computer display or search for the right reading—just show the dial.
Whether you dive with transmitters, SPGs, or both, understanding how your equipment works is key to diving safely and confidently. If you’re unsure about how to check for wear, test accuracy, or calculate your own gas consumption, we’re here to help.
Scuba gear should empower you—not complicate your dive. Trust your training, plan ahead, and use your SPG as the reliable tool it was designed to be.
Questions? Call us at 416-503-3483 and speak to an experienced professional.