Deep Thoughts About: Tanks! From Annie F

The Bomb On Your Back: Testing your Tank!

You’ve all seen the reflective “bumper stickers” on the back of scuba tanks, usually near the lip of the rubber boot that keeps the tanks from falling over: the little sticker with extreme stickiness that has the Dive Utah logo with a month and day stamped out (you’ve probably even taken the ones with only a Dive Utah logo on them). If you have your own tanks, you probably know a little more about them than the average diver, but most divers ask what they are and why dive shop staff care so much about them!

Let’s go for a dive, shall we?

It’s a bright summer day and as you and your buddy think about your plans for the weekend, a dive-along at a nearby dive site, you can almost smell the neoprene and salt air! You are a frequent diver and, in preparation for the big dives, you and your buddy take your buddy’s personal scuba tanks into the local dive shop to get them filled. You’re hoping to get in and out without having to go past the tantalizing dive computer case but after only a moment and a quick glance at your cylinder, the shop staff dashes your dreams. They inhale and meet you and your buddy with every hurried diver’s least favorite words: “Looks like one of your tanks is out of viz. We’ll need to do an inspection,” or (worse yet!), “We’re going to need to get a current hydro on this before we can fill this up.”

You might groan, “How long is that going to take? Great, there go my dive plans!” or even glare at the shop employee (who is helpless and gives you an apologetic grimace, shrugging beneath your scrutinizing gaze), and you may also wonder why these fill station operators are such sticklers. Can’t they just let it slide? One fill! Don’t shop employees want you to go diving??

            Not so fast, eager diver. Let’s talk about what a “viz” is and what a “hydro” is, and why they are so important.  

You may recall from your open water class that scuba tanks need to undergo two different kind of inspections- one is a yearly “viz” (visual) inspection and the other is a hydrostatic inspection, which happens every 5 years. A viz may also need to happen if you completely drain a tank, and a hydrostatic inspection may need to occur if your tank’s previous hydro test has lapsed after 5 years (check the date on the neck- it will look like 05 □14), if a valve’s burst disk ruptures, or if it gets dropped and there is external damage. Let’s go into where these happen, what each entail, and what can happen if you try to ignore them.

What happens during a visual inspection?

Dive Utah has two specially trained and certified cylinder inspectors who know what to look for in order to say with certainty that a tank is good for another year; Steve and Annie. We have a special “to-do list” that we created to help us remember all the steps we need to take and, at the end of an inspection, we like to give a copy to the tank’s owner so they can see if there were any noted issues or things to watch out for.

So…what happens when we take a tank your tank to the garage for a viz?

We first drain the tank, and then use a rubber mallet to loosen the valve.

We take that valve off and inspect the threads and the “dip tube”, a protection which keeps any moisture inside the tank from getting into the first stage on a dive (helpful hint: if you ever hear rattling inside your tank, 9 times out of 10, it’s the dip tube!). We make sure the valve is functioning and we inspect the tank neck O-ring. Once we are done with the valve, we inspect the outside of the tank for corrosion, scratches, pitting or any other issues.

We then go inside the tank and inspect the threads of the neck, the neck itself, and then we insert a light into the tank and s…l…o…w…l…y go around the inside with the beam, checking for any cracks, pits, waves, bubbles, or striations.

            If everything passes, we put the valve back on and refill your tank. When it’s nice and warm from its fill, we scrape the old sticker off and then put the new viz sticker (good for one year!) on the back of the tank. The warmth of a nice toasty fill seems to help those stickers come off a little easier than they do when the tank is cold.

Hydrostatic Testing

Dive Utah doesn’t do hydrostatic testing on-site. We are not set up for that or for tank tumbling. There is a special company locally who tests cylinders being used for everything from diving, to vats holding liquid nitrogen for those fancy new “subzero” ice cream parlors, to oxygen for medical use. Depending on how busy they are, a hydro service can take anywhere from 2-3 days to up to 2 weeks.

When a tank arrives at hydro, the hydro testing facility inspect it themselves, fill the tank with water. After filling it, they will pressurize the tank to a specific amount, testing and checking for stretching or leaks. Tanks should be able to withstand much more than their “working pressure”, the amount stamped into the side of your cylinder. If for some reason they can’t withstand that certain percentage above WP, the tank is condemned. It’s not a “we can try to fix this and test it again” situation either- if a tank fails, it fails for good and is condemned.

My tank was visually condemned and/or hydrostatically condemned- what now?

Perhaps most confusingly of all, just because a tank doesn’t pass a visual inspection doesn’t mean it’s done for. Sometimes we make stipulations- we ask for the owner to get it tumbled to remove rust or calcifications, or we may clean it out with soap and water to remove particulates or other irritants. Once that process is done, it may undergo another visual inspection. Most of the time, at least here at the shop, the tanks we get which are condemned get a red paint-pen mark to demonstrate it has been condemned and we let the customer know why it failed inspection. If it’s a visual inspection, we write up a bit of how the inspection went, and what was the problem. We may explain about why the issue is cause for failure, and, if that reason was interesting enough, we may actually offer compensation in exchange for the tank. We often use a machine to cut out the affected part of the tank and use it as an example for future cylinder inspection courses as well as our Equipment Specialty course. If it’s really really cool, we will take pictures and then post them on our social media, talking about why they’re really neat (for example, check out these stress striations!! These happen when someone MAJORLY overfills a tank).

Are there any kinds of cylinders Dive Utah can’t fill?

The long and short of it is yes; while we can happily fill most cylinders, there are some tanks that we can’t fill.

Some potential customers want their cylinders filled to extremely high pressures; some tanks are specifically designed for this! Certain SCBA tanks, for example (usually used by the fire department or other professions where they use self-contained breathing systems similar to the system we use when we dive), as well as the small mounted pressurized cylinders mounted to paintball guns. They require adapters which we don’t have and, because we don’t get requests to fill them often, don’t carry. We DO fill avalanche bottles (BCA and SnowPulse are our two usuals) though. Being in Utah, especially when a majority of our staff and students are also avid skiers, we do have the adapter necessary to fill avi bottles.

Are there any tanks Dive Utah won’t fill?

Yes- there is one specific kind that we won’t even take back into the garage. That type of tank is a carbon fiber cylinder. These specially created cylinders are regularly pressurized to about 4500psi. Beside the fact that our compressor is not able to fill that high, there is an issue of safety. When carbon fiber tanks are damaged, if they get any kind of moisture inside the wrapped layers of glazed/set material, the water will completely unwind it. And when that happens, it becomes an innocent-looking yet literal bomb.

In our cylinder inspection class, we heard horror stories of cars with carbon fiber tanks exploding and taking people by surprise. We can’t fill them to their proper working pressure, and so we ask that those who own them find someone else to fill them.

Enjoy a news-provided picture of a natural gas vehicle that had a damaged tank and exploded- that feathery looking thing IS THE TANK. When it exploded, it damaged 5 businesses. No thank you.

So! Check your personal cylinders for up-to-date visual inspection stickers, understand why we deliver the news that we cannot fill them or need to test them, and understand the danger that an un-cared-for cylinder can present to both the diver and our dive shop employees.

Part of having a successful dive is having the right equipment- properly maintained and serviced. Make sure that includes your tank!