Perfect Diver Magazine issue 23

tips & curiosities

STAGE CYLINDER (STAGE)

HOW TO BECOME A BETTER DIVER?

Text Wojciech A. Filip

Astage is an additional tank mounted at the side of a diver and taken under water in addition to a single tank or twinset for 3 reasons*:

- as´ an additional bottom gas cylinder

as a decompression gas cylinder

as a gas cylinder for filling/suppling additional devices

How to choose its size? Why recreational divers do not use stages? Current stage cylinder users are invited to refresh their knowledge and those of you who have seen such a tank only in photographs are invited to explore newknowledge.

* This article is about using stage cylinders in the OC backmount configuration, i.e. a situation where the diver is using a single tank or twinset as their basic source of gas.

Photo Jon Borg

ALUMINUM OR STEEL?

Opinions differ in this matter – sometimes people using a stage made from a particular material with a random capacity only because such a tank was at hand and this is how it goes.

My suggestion: aluminum.

If filled even with a very heavy gas (high oxygen content), the tank will have a neutral buoyancy at some 100 bars of pressure (11.1 L capacity). In other words, the tank will not pull the diver to either side and when detached, it will float next to its owner. This will not happen in the case of the smallest 5.7 L aluminum tanks. A good idea is to check how the stage behaves with different amounts of gas.

WHICH CAPACITY?

Theory has it that there is no such thing as too much gas, but having too little can be dangerous. Is an 11.1 L aluminum tank the best? This is a universal gas container. In the case of recreational diving, taking such a tank under water may extend your diving time significantly. If we are planning to only take oxygen in a stage cylinder as a decompression gas and the decompression time with this gas is slightly over ten minutes or so, consider takinga smaller tank. Oxygen is the heaviest of breathing gases that we can take underwater. A large stage cylinder filled with this gas will have negative buoyancy for the entire dive (it will hang low, giving a distinctive overweight feeling). To avoid having to deal with such overweight, you can attach such a tank to your hip d-ringon a special leash, hanging between the diver’s legs. If I do not need a very large amount of oxygen, a smaller tank will bemore convenient.

Photo Mariusz Czajka

HINT

Take your stage cylinder filled up to 200 bar for a simple dive. Breathe gas from it and check the tank’s buoyancy at 50 bar intervals. If you are using 11.1 L tanks (a big aluminum tank, very often called an aluminum 12L), be careful when the pressure is low. A freely released tank will slowly resurface.

Explanation for recreational divers:

when we dive, our dive time usually depends on the amount of gas in ourtank. We very rarely resurface because the planned time ended and much moreoften the pressure gauge arrow is nearing the 50 bar red field.

Things vary slightly when it comesto technical diving. We start planning by determining the amount of decompression gases that we can safely take for the dive, and this in turn will help us determine how long can we stay and how deep can we go. Many stage cylinders look good on photos, but they mostly get in your way while diving.

Why recreational divers do not use stage cylinders?

First, it’s a technical matter. Every diver usinga single tank on their back can add 1, 2 or more stage cylinders without any problems. Before doing so, they should check the capacity of their equipment. Modular buoyancy compensator devices, e.g. Tecline Peanut 21, ensure a vast freedom of movement when diving with 1 tank on the back and several stage cylinders.

I am an AOWD diver. Does it mean that I can dive with additional tanks? I do not recommend this solution without good prior training under the supervision of an experienced trainer, however there is no such training in the recreational diving market. Before diving with a stage cylinder, learn how to plan diving longer than the socalled “no decompression” dives and advanced skills related to properly configuring the equipment and achieve very good buoyancy control.

ADVICE FOR REC DIVERS

Ask your instructor how to calculate gas consumption at different depths. You will see that dive planning is a cool and extremely useful skill. It is like going on vacation somewhere where the number of gas stations is very low. In such a situation you should learn how much fuel does the car take and how far can you go without refueling.

IMPROPER TANK CARRYING AND THE RESULTS IN WATER

Photo Jon Borg

Photo Jon Borg

PROPER TANK CARRYING AND THE RESULTS IN WATER

Photo Jon Borg

Photo Jon Borg

Photo Jon Borg

…meanwhile in technical diving :)

HERE IS SOME USEFUL INFORMATION FOR DIVING WITH STAGE CYLINDERS

1. The stage cylinder harness is used to stabilize the valve and consequently the regulator and pressure gauge in the water. It should be very tight. This way we can not only constantly observe the pressure gauge without the need to turn the tank around, but also freely conduct a modified v-drill. The harness is not intended for carrying the tank (carry the tank by the valve). If carried by the harness on the surface, the tank will turn around its axis in the water once attached to the diver. The valve becomes lowest point, which can easily get caught on guide lines, the 2nd stage regulator hose will be very tight, pulling the regulator out of your mouth and controlling the pressure gauge will require turning the tank every time.

2. Stage cylinder marking, i.e. the socalled MOD sticker, should be placed right below the cylinder bell, on both sides of the tank. Proper attachment is a guarantee of easy gas identification also in difficult conditions (e.g. stress, low visibility). Put the tank on the ground with the valve pointing up. The first MOD sticker is placed so as to allow to read it while standing on the side of the knob, as a numerical value running horizontally, e.g. 21. We attach the same sticker on the other side of the tank.

3. Information on the tank owner should be placed on the bottom part, at a 90 degrees angle to the MOD. If done properly, we can see no other mark while reading the MOD.

4. When diving with 1 stage cylinder, you may shorten the bottom part of the harness so that the tank will not extend beyond the twinset contour when empty. You can do it by putting the bottom snap under the harness counter-clockwise, if the tank is mounted on the left side of the diver (clockwise, if the tank is mounted on the right side). This in turn will improve the tank valve location.

5. If you use 2 or more stage cylinders, usually 2 are left at the front of the diver. We attach the tank emptied from gas closer to the diver’s body. This is how we get an equal position of both tanks (the empty one raisesthe full one slightly) and easier access to the valve of the tank currently used.

Photo Jon Borg

ROTATION OF STAGE CYLINDERS

This means changing tanks under the water (if there are more than 2) so that the tank with the gas needed at a given depth is located in the most convenient position for the diver.

6. During complex dives, the diver canuse more than one stage cylinder. Usually, there are 3 to 6 tanks. Each one contains a gas needed at different depths. In order to move freely and not be overweighted, no more than 2 tanks are mounted on the side of the diver. The rest is attached to special loop scalled “leashes” on the diver’s hipd-rings that you slip between your legs.

7. Overhead diving requires distributing so-called “deposits”. These are stage cylinders mounted to the guideline at specific locations in a cave orwreck. This way the diver has more freedom, because they do not need to constantly transport all the tanks.

8. In open water diving, you may “release” empty tanks to the surface using a line attached to a surface marker buoy. 11.1 L tanks resurface with their bottom up, so it is better to mount them to the line using the top snap. Every organization that trains divers in using stage cylinders is using specific procedures. It is vital to learn them thoroughly and master them. Compare the methods you follow with the ones described in our article. Practical tests will help you find the perfect configuration.

Dive safe, WAF

PS. You can write to the Perfect Diver’s editorial team with any reflections. If you prefer to talk in person, come to the Tecline Academy.

https://teclinediving.eu/tecline-academy/#/