Three scuba cylinders, all holding basically the same volume of air, but each a different size and a different weight. Which one would you want to wear?
When is the last time you took a look over your shoulder at your scuba tank? When’s the last time you gave your tank a second thought? We’re betting it’s been a while.
Most scuba divers who got certified in the last 20 years or so more than likely learned to dive strapped to an 80-cubic-foot aluminum cylinder. And once certified, chances are an aluminum 80 is what you rented, and it’s probably the first tank you bought. Even today, go on vacation to the tropics and you’ll find the tanks your dive resort supplies you with will be, yep, aluminum 80s.
Aluminum 80s are so ubiquitous in today’s dive world that many divers strap them on without giving it a second thought. Is this a bad thing? Not at all. The aluminum 80 is a reliable scuba cylinder, and for many divers it may still be the best choice. But it’s not the only choice.
In recent years both low-pressure and high-pressure scuba cylinders made of chromium molybdenum steel—also known as chromoly—have arrived largely unnoticed on the diving scene. While perhaps not for everyone, these 21st Century cylinders could just possibly change your entire diving experience, both under water and on the surface.
That’s a pretty big claim, to be sure, one that got our investigative juices flowing. So we pulled one of our standard aluminum 80s from the tank rack, along with two of the new steel tanks that also hold approximately 80 cubic feet of gas (a HP steel 80 and a LP steel 85) and we compared them head to head.
Aluminum 80 – Old Reliable
The standard 3,000 psi aluminum 80, currently manufactured by Catalina Cylinders, Luxfer and Worthington Cylinders, hasn’t changed much over the past three decades, and it’s not likely to change much going forward. The popularity of the aluminum 80 boils down to its two biggest advantages, neither of which, ironically, have anything to do with actually using the tank in the water.
First and foremost is price. Running in the neighborhood of $150, a standard aluminum 80 costs about half as much as a steel cylinder offering comparable gas volume. And being aluminum, this tank also doesn’t rust, which theoretically results in lower maintenance costs, especially in high-humidity locales.
Recommended Scuba Diving Tank – Sea Pearls 80
The downsides to standard aluminum 80s start showing themselves when you’re preparing to hit the water. First there’s the weight issue: since aluminum isn’t as strong as steel, the construction of a cylinder has to be beefed up to withstand the 3,000-plus psi pressures. This makes for a heavier tank—between 31 and 32 pounds versus, say, a HP steel 80 which weighs about 30 pounds. (A couple extra pounds may not sound like such a big deal when you’re sitting in front of your laptop, but you may change your tune after a few trips hauling those tanks up and down that stairway to the beach.)
At just under 26 inches, an aluminum 80 is also a taller tank than either a HP steel 80 or a LP steel 85, so it tends to be less comfortable to wear. Both when gearing up and during an actual scuba dive, aluminum 80s are notorious for boinking divers in the back of the head, or in the butt, or both. But without question the biggest downside to an aluminum 80 is the buoyancy issue. A standard aluminum 80 is 1.6 pounds negatively buoyant when topped off with gas, and 2.8 pounds positively buoyant at 500 psi. Also, as pressure gets down to 500 psi, the tank boot end of an aluminum 80 tends to get more buoyant than the valve end (how many times have you seen divers at their safety stops with the bottoms of their tanks lifting away from their backs while the tank valve knocks them in the head?). This is not only annoying, it also messes up your trim at the end of a dive.
Finally, a standard aluminum 80 actually carries less gas than comparable steel tanks. When filled to its rated 3,000 psi, the aluminum 80 offers only 77.4 cubic feet of gas. Casual recreational divers might not mind being short-changed by 2.6 cubic feet, but to serious bubble-blowers who like to squeeze every minute of bottom time out of their dives, this means possibly running short of gas just when things start getting interesting.
Note: The above is based on the performance attributes of a “standard” aluminum 80. There are, in fact, a couple “specialized” aluminum 80 models that have slightly better buoyancy characteristics (Catalina’s C80, for example), but they cost quite a bit more too.
HP Steel 80 – New Kid on the Block
While low-pressure steel tanks have been around since Jacques Cousteau started diving, high-pressure steel tanks, manufactured by Worthington Cylinders and Faber, are relatively new to the diving scene. It takes only a dive or two strapped to a high-pressure steel tank to become a fan. First and foremost, these cylinders can store some gas. A full fill at 3,442 psi on a HP steel 80 will actually give you 81 cubic feet of gas volume. More gas equals more bottom time. A HP steel 80 is also a couple pounds lighter than an aluminum 80 and about six inches shorter, which means the tank that’s packing more gas is also a more compact package that rides more comfortably on your back.
Recommended Scuba Diving Tank – Faber FX Series 80
But best of all, the HP steel 80’s buoyancy characteristics simply can’t be beat. At nine pounds negative buoyancy when full and three pounds negative buoyancy when empty, a properly-weighted diver switching from an aluminum 80 to a HP steel 80 could theoretically take six pounds off his or her weight system. In a sport where minimizing ballast has a direct effect on your comfort, mobility and overall enjoyment in the water, this is major.
However, all this sweet stuff comes at a cost—like around 300 bucks. And if that isn’t painful enough, the higher service pressure of 3,442 psi that enables a HP steel 80 to hold so much gas is not available everywhere. If there’s no one in your neighborhood able to crank the pressure high enough to give you a full fill, you’ve lost a major motivation for owning this tank.
LP steel 85 – Low Pressure, High Volume
The LP steel 85 is a more efficient remake of the low pressure steel 72s that were the tanks of choice back in the ‘60s and ‘70s. Divers who love the buoyancy benefits of a steel cylinder but don’t have access to high-pressure fill stations will probably gravitate to the LP steel 85. Able to maximize gas volume at a lower fill pressure, a LP steel 85, at a fill pressure of, say, 2,640 psi, will deliver almost 83 cubic feet of gas volume—outshining even the HP steel 80 for increasing your bottom time.
Recommended Scuba Diving Tank – Faber Low Pressure 85 Steel Tank
Dimension-wise, a LP steel 85 is not that much different than an aluminum 80—about an inch shorter, a few pounds heavier. However, its buoyancy characteristics are much better. At just over seven pounds negative buoyancy full and .7 pounds negative buoyancy at 500 psi, a properly weighted diver switching from an aluminum 80 to a LP steel 85 could theoretically remove about 3.5 pounds from his or her weight system.
The downside is, like the HP steel 80, the LP steel 85, offered at around $275, is substantially pricier than an aluminum 80, and it is steel, so it can rust, although it generally won’t if you make even a minimal effort at rinsing it down with fresh water after a dive.
For divers on a strict budget or who live in the tropics, the aluminum 80 is a perfectly workable way to haul around your breathing gas. For divers looking for maximum volume in a small, relatively lightweight tank that’s easy to wear, plus allows you the opportunity to shed up to six pounds from your ballast system, the HP steel 80 is the ticket—IF you have access to high-pressure fill stations. If you don’t, the LP steel 85—a bit larger, a bit heavier, but with similar buoyancy characteristics, would be your best bet.
Each route will be the right route for some divers, and the wrong route for others. It all depends on individual diving styles, diving locales and budgets. It’s just nice to know that, even when it comes to scuba tanks, we do have choices.
A Dual-Purpose Tank
During our investigation into HP steel cylinders we discovered another cylinder that’s only slightly larger than the HP steel 80, yet offers a level of gas volume that will make you simply giddy, regardless of where you happen to get it filled. It’s called the HP steel 100.
This versatile tank provides 99.5 cubic feet of gas with a 3,442 psi fill, and 87 cubic feet of gas with a 3,000 psi fill. That’s 10 cubic feet more gas than you’d get with an aluminum 80, and 17 cubic feet more gas than a HP steel 80 at the same fill pressure. So even when you can’t hook into a high-pressure fill station you can still score a hefty load of gas for extended bottom time, with a tank that’s very similar in size and weight to a HP steel 80.
Also, like the HP steel 80, the HP steel 100 has excellent buoyancy characteristics. Ranging from 10 pounds negative when full to 2.5 pounds negative when empty, a properly weighted diver switching from an aluminum 80 to a HP steel 100 could theoretically shed five and a half pounds from his or her weight system.
Selling for about $355, it’s pricier than the steel 80s mentioned above, but with its similar size and buoyancy characteristics, and its ability to offer a substantial increase in gas volume, regardless of where it’s filled, the HP steel 100 is RDC’s choice as the best all-around tank for serious divers looking to increase diving comfort as well as bottom time.
A Few Words on Tank Valves
There are now three options available when choosing a tank valve. The most basic is the standard yoke-style “K-valve,” then there’s the combination yoke/DIN valve that features a removable insert that lets you easily convert a yoke-style valve into a 230-bar DIN valve, and finally there’s the dedicated 300-bar DIN valve.
Our favorite is the combination DIN/yoke style, because it allows you to use either a yoke or a DIN regulator on the same tank. Even better, a DIN/yoke style valve costs only a few bucks more than a basic K-Valve.
You can also now get tank valves that are ready for nitrox service right out of the box. These valves come with Viton and EPDM O-rings, Christo-lube lubrication, and nylon seat material. It’s much cheaper to buy a valve that’s nitrox-ready than to have a standard valve prepped for nitrox. In fact, the difference in price between a basic yoke valve designed for air-only service, and a DIN/yoke convertible valve with nitrox-ready components, is only about 10 bucks.
Valves are also safer now with one-piece shielded burst discs and color-coded valve handles. The burst disc is designed to rupture and vent air if the internal pressure gets too high due to overfilling or excessive external temperature. This new design uses a one-piece assembly that is recessed into the valve to prevent damage or injury if ruptured.
Some tanks now come with valves handles that have color-coded sleeves, providing an easy visual indication if the valve is closed (red) or open (green) or somewhere in between. These are also available as aftermarket items for retro-fitting on your current tank valve.
While tanks and valves require little maintenance other than a good rinse, manufacturers recommend having the valve serviced at least every five years when the cylinder is taken out of service for the DOT required Hydrostatic test. O-rings, seats and the burst disc assembly should be replaced at this time.
I’ve been a diving addict since my 14th birthday when my parents took me to the Bahamas and had my first scuba diving experience. I’ve been an active diver ever since but in the last few years my focus shifted on sharing my thoughts and experience on diving gear, writing product reviews and gave up on organizing dive tours.