1At a glance
- Typical Operating Pressure (Steel)
- 200-232 bar (3,000-3,500 psi)
- Typical Operating Pressure (Aluminium)
- 138-207 bar (2,000-3,000 psi)
- Common Capacity (Litres)
- 10, 12, 15, 18 litres
- Common Capacity (Cubic Feet)
- 80, 100 cubic feet (cf)
- Material Options
- Aluminium alloy, Steel alloy
- Valve Types
- DIN, Yoke (A-Clamp)
- Inspection Requirements
- Visual inspection annually, Hydrostatic test every 5 years (international standards)
2How scuba tanks work and are maintained
A scuba tank functions as a reservoir for compressed breathing gas, usually air or enriched air nitrox. The gas is stored at high pressure within the cylinder, and its volume is measured in litres (cubic feet). A valve assembly at the top of the tank regulates the outflow of gas. When a regulator is attached, it reduces the high pressure from the tank to a breathable pressure, delivering it to the diver.
Tanks are constructed from either aluminium or steel alloys. Aluminium tanks are generally lighter out of water, but become positively buoyant when empty. Steel tanks are heavier overall and tend to remain negatively buoyant even when empty, which can reduce the amount of weight a diver needs to carry on their weight belt. Both types are designed to withstand extreme pressures and are rigorously tested during manufacturing.
Regular maintenance and inspection are crucial for scuba tank safety. This includes an annual visual inspection (VIP) to check for internal and external corrosion, damage, and thread integrity, and a hydrostatic test every five years (though this can vary by region) to verify the tank's structural integrity under extreme pressure. Proper storage, avoiding extreme temperatures, and never completely emptying a tank to prevent moisture ingress are also key practices.
3Aluminium vs. Steel Scuba Tanks
| Feature | Aluminium Tanks | Steel Tanks |
|---|---|---|
| Material Composition | Aluminium alloy (e.g., 6061-T6) | High-strength steel alloy |
| Out-of-Water Weight | Lighter | Heavier |
| Buoyancy Characteristics | Negatively buoyant when full, becomes positively buoyant when empty. | Negatively buoyant when full, remains negatively or neutrally buoyant when empty. |
| Corrosion Resistance | More resistant to external corrosion, but susceptible to internal pitting. | More susceptible to external rust if uncoated, high resistance to internal corrosion when properly maintained. |
| Typical Maximum Pressure | 138-207 bar (2,000-3,000 psi) | 200-300 bar (3,000-4,350 psi) |
| Durability/Impact Resistance | Can dent; threads can be more fragile. | More impact-resistant; threads are generally more robust. |
4What scuba tanks mean for your liveaboard trip
On a liveaboard, scuba tanks are typically provided as part of your package, simplifying logistics. The crew manages the filling and placement of tanks, often setting them up on the dive deck with your BCD and regulator for each dive. This convenience allows divers to focus on preparing themselves rather than handling heavy cylinders.
Liveaboards usually carry a range of tank sizes, with 12-litre (80 cf) or 15-litre (100 cf) being the most common. If you have a high air consumption rate, or are doing deeper or longer dives, requesting a larger tank (e.g., 18-litre or 100 cf) in advance is advisable. Similarly, smaller tanks may be available for divers with lower air consumption or children.
Divers also need to be aware of the tank valve type – DIN or Yoke. Liveaboards usually have tanks with convertible valves or adapters, but it's always good practice to confirm compatibility with your regulator before travel. Many liveaboards also offer Nitrox fills, which require dedicated tanks or thorough cleaning procedures if tanks are swapped between air and Nitrox use.
5Common Scuba Tank Specifications and Uses
| Tank Type | Volume (Litres) | Volume (Cubic Feet) | Common Use Cases |
|---|---|---|---|
| Aluminium 80 (AL80) | 11.1 litres | 80 cf | Most common recreational tank, widely used for single-tank dives. |
| Aluminium 63 (AL63) | 8.7 litres | 63 cf | Often used as pony bottles or for divers with very low air consumption. |
| Steel 12L | 12 litres | 80 cf (approx.) | Popular recreational tank, especially where negative buoyancy is preferred. |
| Steel 15L | 15 litres | 100 cf (approx.) | Used by divers with higher air consumption, or for longer/deeper recreational dives. |
| Steel 18L | 18 litres | 120 cf (approx.) | Primarily for technical diving, extended bottom times, or very high consumption divers. |
6Common misconceptions
Myth: Scuba tanks are filled with pure oxygen. Fact: Recreational scuba tanks are typically filled with compressed air (79% nitrogen, 21% oxygen), or enriched air nitrox (EANx) with a higher oxygen percentage (e.g., 32% or 36%). Pure oxygen is highly toxic at depth and is only used for very specific technical diving applications, often at shallow depths for decompression stops.
Myth: A full tank of air lasts a fixed amount of time. Fact: How long a tank lasts depends entirely on the diver's air consumption rate (SAC rate), which varies with individual fitness, stress levels, depth, workload, and experience. Deeper dives consume gas faster due to increased ambient pressure, and factors like current or exertion also increase consumption.
Myth: Tanks can explode if dropped. Fact: Scuba tanks are built to extremely high safety standards and are incredibly robust. While dropping a tank can damage the valve or the tank itself, leading to gas leakage or rendering it unsafe for future use, an explosion due to a simple drop is highly unlikely. Proper handling, however, is always essential to prevent damage.
Myth: All tanks have the same connection for regulators. Fact: There are two main types of regulator connections: Yoke (or A-Clamp) and DIN. While many modern tanks or valves are convertible or adapters are available, divers must ensure their regulator matches the tank valve type available at the dive centre or on the liveaboard. Most liveaboards are equipped for both.
FAQ
What gas is inside a scuba tank?
Most recreational scuba tanks are filled with compressed air, which is a mixture of approximately 21% oxygen and 79% nitrogen. Some divers use enriched air nitrox, which has a higher percentage of oxygen and a lower percentage of nitrogen.
How do I know what size tank I need?
The ideal tank size depends on your air consumption rate, the depth and duration of your planned dives, and your physical comfort. Most liveaboards provide 12-litre (80 cf) tanks, but larger 15-litre (100 cf) tanks are often available for divers who consume more air.
What's the difference between DIN and Yoke valves?
A Yoke (or A-Clamp) valve secures the regulator to the tank with a clamp. A DIN valve screws directly into the tank's outlet, providing a more secure metal-to-metal seal. Many liveaboards offer tanks with convertible valves or have adapters available for both types.
Are scuba tanks made of aluminium or steel?
Scuba tanks are typically made from either aluminium alloy or steel alloy. Aluminium tanks are generally lighter out of water and become buoyant when empty. Steel tanks are heavier and tend to remain negatively buoyant even when empty, requiring less weight on the diver's belt.
How often are scuba tanks inspected?
Scuba tanks typically undergo an annual visual inspection (VIP) to check for internal and external damage. They also require a hydrostatic test every five years (though this can vary by region) to verify their structural integrity under high pressure.
Can I use my own scuba tank on a liveaboard?
While possible, it is generally not practical or necessary as liveaboards provide tanks as part of the package. Transporting personal tanks can be complex and expensive due to airline restrictions and weight limits. Always check with the liveaboard operator if you wish to bring your own specialized tank.