Proper Post-Dive Maintenance for Your Small Diving Tank
To clean and store a small diving tank after a dive, you must immediately rinse it with fresh water, internally and externally, to remove salt, chlorine, sand, and biological contaminants. After rinsing, you must drain it completely and store it in a cool, dry place with about 200-500 PSI of pressure inside to prevent moisture ingress. The entire process is a non-negotiable routine that directly impacts the tank’s structural integrity, your safety, and the longevity of your investment. Neglecting even one step can lead to costly hydrostatic tests failing or, in a worst-case scenario, a catastrophic tank failure.
The first and most critical step begins the moment you exit the water. Saltwater is highly corrosive, and even chlorinated pool water can degrade valves and fittings over time. Sand and microscopic organic matter can clog valves and create pockets for corrosion to start. Here’s the immediate post-dive action plan:
External Rinse: Use a hose with a gentle spray attachment. Never use a high-pressure nozzle, as it can force water past the O-ring into the valve. Thoroughly spray the entire exterior, paying close attention to the tank boot (if equipped), the valve assembly, and any grooves or threads. Scrub lightly with a soft brush to remove any stubborn debris or algae.
Internal Rinse (The Most Overlooked Step): This is crucial. You need a specialized tank rinsing tool that connects to your hose and has a long tube to reach the bottom of the tank. Fill the tank about one-third full with fresh, clean water. Recap the valve and agitate the tank vigorously by rolling it and shaking it for at least 60 seconds. This sloshing action dislodges any moisture or contaminants that condensed inside during the dive. Drain the tank completely by inverting it and opening the valve slightly to let the water flow out. Repeat this internal rinse at least twice until the water runs completely clear.
After the thorough rinse, drying is paramount. Any residual moisture inside the tank is the primary enemy, leading to internal corrosion that can weaken the metal from the inside out. Follow this drying procedure meticulously:
1. Leave the valve slightly open (cracked).
2. Invert the tank and place it on a soft, stable surface, like a carpet scrap or in its storage rack, to allow all water to drain from the neck.
3. Let it air dry in a well-ventilated area away from direct sunlight for a minimum of 2-4 hours, or ideally overnight.
Once you are confident the tank is completely dry, you must prepare it for storage. This is not simply putting it in a closet. The correct storage procedure preserves the tank’s pressure integrity.
Pressure Retention: You should never store a tank completely empty. A small amount of positive pressure, typically recommended to be between 200 and 500 PSI (14-34 bar), must be left inside. This serves a vital purpose: it prevents ambient moist air from being drawn into the tank. If a tank is stored at zero pressure, temperature fluctuations can cause the internal air to contract and expand, sucking in humid air that will condense and cause internal corrosion.
Valve Protection: Screw the plastic valve cover back on securely. This protects the critical valve threads and the O-ring seat from damage, dust, and insects.
Understanding the Science of Tank Corrosion
To appreciate the cleaning ritual, you need to understand what you’re fighting. The two main types of corrosion that affect diving tanks are general corrosion and sustained load cracking.
General Corrosion: This is the gradual degradation of the metal surface caused by a chemical or electrochemical reaction with the environment. In a diving tank, the electrolyte is water—specifically, water contaminated with salts or chlorides. The reaction creates rust (iron oxide for steel tanks) or aluminum oxide. Internal corrosion is particularly dangerous because it’s hidden from view and can significantly reduce the wall thickness of the tank, compromising its strength. The following table outlines the key differences between aluminum and steel tanks regarding corrosion.
| Factor | Aluminum Tank | Steel Tank |
|---|---|---|
| Primary Corrosion Type | Pitting Corrosion. Creates small, deep pits rather than widespread rust. | General Surface Rust. Appears as a reddish-brown coating. |
| Visual Indicator | White, powdery aluminum oxide coating inside. | Flaky or pitted reddish-brown rust inside. |
Hydro Test Impact| Pitting can lead to failure if deep enough to compromise minimum wall thickness. | Rust can be “tumbled” out if superficial, but pitting is a serious concern. | |
| Susceptibility to Moisture | Highly susceptible. Aluminum oxide layer can be penetrated by chlorides. | Highly susceptible, especially if the interior paint or coating is compromised. |
Sustained Load Cracking (SLC): This is a more complex failure mode. It occurs when a small crack, often initiated by a corrosion pit or a microscopic manufacturing flaw, slowly grows over time under the constant high pressure (the sustained load) inside the tank. Proper cleaning and drying directly combat this by eliminating the corrosion pits that can be the starting point for SLC.
The Non-Negotiables: Visual Inspections and Hydrostatic Tests
Your cleaning and storage routine is only one part of the safety triangle. Regular professional inspections are mandated by law and common sense.
Visual Inspection (VIP): This should be performed by a certified inspector annually. The inspector will remove the valve and use a specialized borescope (a tiny camera on a flexible cable) to examine the entire interior surface of the tank for any signs of corrosion, pitting, or contamination. They will also inspect the exterior for dents, gouges, and thread integrity. A failed visual inspection means your tank cannot be filled until the issue is resolved, which sometimes is impossible, meaning the tank must be condemned.
Hydrostatic Test: This is a test of the tank’s structural strength and elasticity. It is required every 5 years in most countries, including the United States (per DOT regulations). The tank is placed inside a water-filled chamber (a “hydrotest bomb”) and pressurized to 5/3 of its working pressure. For a standard 3000 PSI tank, that means it’s pressurized to 5000 PSI. The technician measures the permanent expansion of the tank. If the tank does not return to its original size after the pressure is released, it fails the test and is permanently condemned, typically by drilling a hole through the shoulder.
Creating the Ideal Long-Term Storage Environment
Where and how you store your tank between diving seasons is as important as the immediate cleaning. The ideal storage location has three key characteristics: cool, dry, and stable.
Temperature: Store the tank in an area with a stable, moderate temperature. Avoid garages or sheds where temperatures can exceed 100°F (38°C) or drop below freezing. Extreme heat can potentially affect the temper of the metal over very long periods, while freezing can cause any residual moisture to expand.
Humidity: This is the storage killer. The storage area must have low humidity. A basement with a dehumidifier is far better than a dry but hot attic. The goal is to prevent any moisture from condensing on or inside the tank.
Position & Security: Store the tank upright in a dedicated tank rack or securely propped against a wall where it cannot fall over. A falling tank can damage the valve, create a dangerous projectile if the valve is sheared off, or cause a dent in the tank body which is a cause for immediate failure during a visual inspection. If you own a high-quality small diving tank, protecting it with proper storage is the final step in ensuring its decade-long service life.
Finally, be mindful of what you put in your tank. Only use air from a reputable dive shop that specializes in breathing air for scuba diving. Regular industrial compressed air or, worse, gas station air, contains oils, hydrocarbons, and excessive moisture that will contaminate your tank and create a serious health risk and a corrosive environment. The air should meet or exceed the CGA Grade E (United States) or ISO 8573-1:2010 [Class 0] (international) standard for breathing air. This is non-negotiable for your safety.