Deciphering Cylinder-Neck Hieroglyphics

For many divers, the markings around the neck(top) of the tank may well be like reading hieroglyphics. The only real numbers most divers need to know is the tank pressure that the tank will hold, the annual inspection date, and when the periodic tank inspection is due. I will talk about all these as well as the metal types of the of most popular tanks. All dive shop owners will be able to help you interrupt the markings as well as taking care of your tank. Please visit your local dive shop for more information. The marking are not hard to learn and I will attempt to take the mystery out of the markings.



FIRST ROW
GOVERNMENT APPROVAL
First set of letters either DOT or DOT/CTC. These stand for US Department of transportation and the Canadian Transportation Commission. If you travel to Canada and take tanks across the boarder, make sure it has this CTC marking on it. Most tanks sold in the US have the DOT stamp on it.

METAL TYPE
Next set of letters tell what type metal the tank is made from. The 3A denotes carbon steel. Used for early tanks. This tank more prone to corrosion than chrome steel of aluminum.

The 3AA stands for chrome-molybdenum steel. It appears on virtually all steel tanks today.

Aluminum cylinders may bear the designations SP6498, E6498, or most times it is 3AL. First two designations identify permit numbers under which aluminum cylinders are manufactured. But the 3AL is the usual mark you will see on tanks manufactured in the US after July 1, 1982.

WORKING PRESSURE
The next set of numbers, usually four, is the working pressure of the tank. This is expressed in pounds-per-square inch. The cylinder should not be filled past this point. The single exception to this is when you see a + sign at the end of the second row or next to this pressure. That plus sign is usually assigned to steel tank and means you can fill by 10% increase. Most aluminum tanks go to 3000 psi, a few go to 3300 psi. You need to look at this to see what your tank is rated at. Of course the dive shop you take you tanks to will look at this number.

SUBSEQUENT ROWS
SERIAL NUMBERS
Some tanks have a second row while others may have more. All tanks have an unique number assigned to them to identify the tank, this is the serial number. May represent the size and lot number.

MANUFACTURER IDENTIFICATION
This usually follows the serial number and describes the dealer who made the tank. PST is Pressed Steel Company, Luxfer, and Kidde are the common.

HYDROSTATIC DATE
The cylinders initial date follows the manufacturer name. It consist of numbers representing month and year that the cylinder was tested. These numbers will be separated by the hydrostatic tester's initials or a special symbol that the tested had registered with the DOT. Each tank needs to be re-tested every 5 years. Each 5 year test date will appear somewhere at the top around the neck.

This is a brief explanation of tank markings. Like I mentioned above, ask you local dive shop to help you determine what your specific markings mean.

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B.W.R.A.F.-What Does That Mean and Is It Important

If you were a pilot getting ready to fly a plane, no matter what size or type, there are certain things you must do before you leave the ground for the 'wide blue yonder'. That one thing is a basic inspection of the plane. They call this a pre-flight inspection. They check the gauges, make sure they have fuel in the wings, make sure all controls are "free and clear." They do this because, if they found something wrong, the pilot or crew could take care of it on the ground better than in the air. Make sense.



As in diving, we have a similar inspection, we call it the BWRAF (Begin With Review And Friend.) I will cover what each letter means and some important points to each. It is important to always dive with a buddy. Your buddy will do this brief inspection on you and then you will return the favor. Your buddy can also help you get your gear on and off. So DIVE WITH A BUDDY.

B - BCD (BUOYANCY COMPENSATION DEVICE)

Make sure that it is the correct size, and that there are no obvious problems with it. Do an over-all look at it. Is it torn in places that cause a problem, does it "just look" safe ? Check the inflators, do they work, both orally and manually.

W - WEIGHTS and WEIGHT SYSTEMS

Did they remember to put them in. You do not want to be in the water and forget your weights. I have seen divers that did it. Is the amount weight they have fit the suit and water they are going to dive. Are you diving with a wet suit or dry suit; fresh water or salt water; it does makes a difference.

R - RELEASES

Do you know where every one is located ? Start at the top and work your way down. They may have a chest strap, belly strap, and cumber bun. Don't forget to look at the weight system they have. Integrated or external ? If they are using a weight belt, do they have a right hand release ? Check them all.


A - AIR SUPPLY

Check the valve to make sure the air is on. There is nothing worse than getting in the water and forgetting to turn your air on. Check your air gauge and make sure you have enough air for the dive you plan to make. Are you making a long, deep dive - get a fresh tank. Short shallow dive may be able to use less than a full tank. But know before you get in the water. Lastly, taste the air to ensure that is it not stale. Put the regulator in your mouth and take a few breathes and taste it.


F - FRIEND - FINAL OK

Do a final look over your buddy's system to ensure that you did not forget anything. That you have all your equipment in place, that nothing is dangling.If all is OK, then give your dive buddy a 'thumbs' up.

After you do this, have your buddy return the favor. This only takes about 5 minutes, but it is time well spent.

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Buoyancy Control - Explain what it is and why it is important when we dive

Buoyancy is the force that causes an object to float or sink, and can be described as an upward force exerted on any object placed in a fluid, whether it sinks or floats. Wow, what does that mean ? Means that a force equal to the weight of the fluid displaced by the object. A heavy object will displaced more fluid and sink, while a light object will displace less fluid and rise. This principle is best known as the Archimedes Principle.

With all this being said, there are 3 types of buoyancy. They are positive, negative and neutral buoyancy. If any object weighs less than the water it displaces, we call this positively buoyant. If an object weighs more than the water it displaces, we call this negatively buoyant. And finally, if the object and the water weigh the same, this is neutrally buoyant.



Ascend is the positive side, meaning that you are lighter than the water you displace and you will rise or float. Descend is the negative side where you are heavier than the water and will sink. As divers we need to strive to maintain neutral buoyancy like the diver in the middle.

So as in diving, when we enter the water and we are at the surface we are displaying positive buoyancy. When it is time for us to go under the water, we will become heavier than the water to allow us to be negatively buoyant. Once underwater, and at our depth, we will maintain a neutral state, and hover.

Buoyancy is important for two reasons, one at the surface and one underwater. At the surface we are positive, and we float thereby conserving energy. While underwater we should maintain a neutral position so we can stay off the bottom, and avoid crushing or damaging delicate aquatic life and plants.

Buoyancy control is one of the most important skills you can learn and master as a diver. It is a skill that you will improve on dive after dive. On every dive you must continue to fine tune your buoyancy skills. Good buoyancy skills means that your dive will be fun and effortless.

Lastly, keep in mind salt water verses fresh water has different effects on buoyancy which we will discuss on future lessons. Until next time, "Make Every Dive a Good Dive, and Let's Get Wet."

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