Depending on where you’re diving, you may know them as scuba cylinders, tanks or bottles. These aluminum or steel vessels retain our breathing gas at incredibly high pressures. Modern regulators then convert that high-pressure gas to intermediate and then ambient pressure, meaning that, whatever your depth, you should receive a smooth flow of breathing gas.
When it comes to our dive equipment, we often forget about our scuba cylinder. Yet it is vital. We often take for granted that our cylinders are safe, and that dive staff has tested and properly cared for them. But if a cylinder “goes bad,” it can have life-changing (or even life-ending) consequences for the diver or whomever is filling it. Scuba cylinders leave the factory tested to strict engineering standards. However, once in use — much like your car or motorcycle — the onus and responsibility for cylinder care lies with the user.
Impact damage to cylinder walls, valve damage and moisture entering the internals of the cylinder are most concerning. With that in mind, here are some practical hints and tips when it comes to taking care of scuba cylinders.
Care of scuba cylinders
- Don’t leave your cylinder standing up unattended or transport it in an upright position, unless you secure it well. Impact can damage cylinders, which compromises their structural integrity. Don’t leave them in a position where they may fall over. Also, if your cylinder rolls over someone’s toes on a boat, you will not be popular.
- Impact damage can also affect cylinder valves. When transporting cylinders in a vehicle, lay them down, but not in a position where other items can knock into or crush the valve. The vehicle’s movement can also negatively impact a cylinder valve.
- Be gentle with the cylinder valve. Don’t wrench it open or shut it forcefully. Closing the valve extremely hard can damage the valve seat. Similarly, when opening the valve, turn gently until you reach the “fully on” position, then make a small semi-turn back. If you’re technical diving, leave the cylinder fully open to avoid confusion on gas shut-downs.
- Just as with your other gear, rinse the valve and cylinder with fresh water at the end of your dive trip.
- Always store your cylinder with a small amount of gas inside, e.g. 200 to 300 psi or 10 to 20 bar. This reduces the chances of moisture entering the tank. If you’re filling your tank, don’t inadvertently force moisture into the cylinder when filling. Be sure the cylinder valve is dry before connecting the compressor whip. An experienced compressor operator will give the cylinder and whip a little blast or wipe. This will remove any moisture before connecting the two.
- Only a reputable dive center or trustworthy source should fill your cylinder. Moisture can contaminate the tank from poorly maintained compressors where the air is not correctly filtered. This leads to internal corrosion and potentially bad consequences.
Cylinders require regular testing to check their strength and function. Depending on where you are, a regular combination of visual and hydrostatic testing will be necessary.
If you’re using or, especially, filling a cylinder, always check that it is “in test.” Look for the IDEST sticker or stamp, or ask the dive operator for evidence that the cylinder is serviced. And don’t be surprised if a dive center won’t fill your cylinder without evidence that you’ve hof the required testing.
Visual testing is often an annual affair. Dive centers will completely drain the cylinders and remove the valves. Then, the servicing engineer will visually inspect the tank walls for damage, pitting and corrosion. He or she will often service the valve at the same time.
Hydrostatic testing, sometimes known as a “hydro test” by divers, sometimes alternates — depending on location — with the simpler visual test. During a hydrostatic test, the scuba cylinder is filled with water and pressurized to a massive 5/3 of its working pressure. Testers measure the “flexing” of the cylinder wall to ensure that it still retains elasticity and structural safety. Water can’t be compressed. Therefore, if the cylinder is defective it won’t explode if it fails, as it would when pumped with compressed air.
When scuba cylinders go bad
Of everything that could go wrong with a cylinder, luckily, explosions are rare. Of those few recorded failures, most appear to be with the sometimes-more brittle aluminum cylinders. These instances are statistically very small in comparison to the millions of cylinders in circulation worldwide, but there are a few other issues that can arise with cylinders.
Always undertake visual checks, particularly when renting a cylinder. When the shop assigns you a cylinder, look for a service or test sticker or stamp on its side. Requirements and markings vary from location to location so if you’re not sure, ask one of the dive team.
Dive center staff often load dozens of cylinders from boats and trucks and inevitably tanks may become scratched or sometimes damaged. Expect light scratches on the exterior, but if you see severe, deep scratches or dents, point them out to dive center staff for further investigation and, also, for their safety when they fill the tank.
Internal corrosion can lead to a full failure when filling a cylinder, but more likely on the first instance is contamination of breathing gas. Complete a pre-dive safety check on each dive and take a few breaths from your regulator. Does the gas taste strange? Tell the staff if you have any concerns.
Leaks are one of the most common wear-and-tear issues when it comes to cylinders. When you first set up your scuba unit, make sure the O-ring in the cylinder valve is in good condition. Listen for leaks and hisses. If gas is escaping, try re-seating your first stage or ask the dive crew to change the O-ring. If the hissing is coming from where the valve joins the tank, it may not be tightened to the correct torque setting. Equally worrying, there may be tiny cracks at the neck of the tank. Either way, report it to the dive crew.
Cylinder valves that are stiff to open, close or turn are relatively common as they near their service date. If the valve itself is leaking, report your concerns.
Don’t leave the care, regular testing and maintenance of your own scuba cylinders as an afterthought to your equipment preparation. And if you’re renting a cylinder, make sure it’s been tested, is in reasonable condition and that the gas tastes okay before diving with it. If in doubt, speak with the dive operator.