A scuba set – or also called scuba gear – allows breathing and the possibility of free movement underwater. It is also referred to as SCUBA (self-contained underwater breathing apparatus).
Basic knowledge for Open Water Diver* (OWD*)
A diving cylinder is one component of a scuba set. It consists of the cylinder itself, a valve and a boot. The cylinder is made of either steel, aluminum or – rarely used in recreational diving – carbon and glass fiber reinforced plastic. Diving cylinders are filled either with a compressor or from large storage cylinders.
Cylinders especially for diving are offered with a volume of 5, 7, 8, 10, 12, 15 and 20 liters. The choice of the cylinder size depends on physique, use, depth and time. The most common sizes in recreational diving are 10 l, 12 l and 15 l. Most diving cylinders are filled with a pressure of 200 bar. There are also cylinders available that can be filled up to 300 bar. Be aware that if you buy a 300 bar cylinder, the valve and the first stage of your regulator must be rated accordingly. Depending on the manufacturing process, the cylinder weight (without valve) is 10% to 15% higher than the volume and is engraved in the neck of the cylinder. Because of the lower strength of aluminum, the wall thickness must be much larger compared to steel. Therefore aluminum cylinders are about 2 kg heavier than steel cylinders.
Diving cylinders must undergo a visual inspection and pressure test regularly, depending on national regulations and laws. The date (year / month) of the next test is engraved on the bottleneck together with the stamp or sticker of the testing facility.
To protect against damage to the tank surface and to ensure a secure stand each cylinder should be equipped with a boot. You should remove the boot every now and then and check the surface for rusty spots. Diving cylinders should always be stored in a dry place and in an upright position. Always leave at least 30 bar in your tank to avoid moister entering the inside.
Special care has to be taken when carrying your diving cylinder in a vehicle. Make sure it is properly secured against any movement. Be aware that local laws may regulate the transport of compressed air cylinders in private vehicles. Local laws may have also different regulations for carrying diving cylinders in commercial vehicles. Dive boats are usually equipped with holders to prevent the cylinders from rolling around. Taking your scuba set out on a private boat or yacht, make sure the cylinder is secure tight down and the valve is closed. The scuba set should be assembled just before the dive.
When diving in areas with water temperatures below +10°C, two regulators should be installed due to the danger of icing. In the event of icing, the valve outlet for the main regulator can be closed by the diver himself or by its buddy. Handles in different colors are recommended, as it should be clear in the event of icing which handle must be closed. If only one regulator is mounted on such valves, the second outlet must be sealed with an appropriate screw, otherwise water can enter into the area of the upper spindle. The water then enters the cylinder when filling through this outlet and can cause internal icing of the regulator.
In most European countries, valves are provided with a DIN connection. There are screw-in adapters for mounting regulators with INT connections. The valve is fitted with a water protection tube inside the diving cylinder to prevent rust or water from entering the regulator when descending head down. It is better to have a sintered filter installed instead of the water protection pipe.
The installation of a valve on the diving cylinder may only be carried out by a specialist. Incorrect installation or wrong combination can cause mortal danger!
All information can be found in the article Regulator.
All information can be found in the article Buoyancy control device.
- Preparation: Place the diving cylinder on a straight and clean surface in front of you with the valve opening facing away from you. Place the regulator and the BCD within reach.
- Mount BCD: Hold the BCD on the side of the cylinder facing away from you (the side on which the valve opening is located) and put the tank strap over the cylinder. Place the strap so that the top edge of the BCD is at about the same height as the position where the cylinder valve is mounted to to diving cylinder. Make sure the tank strap is properly tightened. It is good practice to wet the tank strap before mounting the BCD to the cylinder. This way the strap already stretches to its maximum while tightening it and does not get loose when you enter the water.
- Install regulator: First check the high pressure inlet of the regulator. It must be dry and the O-ring clean and undamaged in place. The regulator must be mounted an a way that the main second stage and the octopus are on your right hand side and the SPG and inflator hose on your left hand side. Screw the first stage with the hand wheel hand-tight into the valve opening. Then connect inflator hose with the inflator.
- Open valve: Hold the window of the SPG towards the floor and open the cylinder valve slowly until you hear the air flowing into the system. Soon as your regulator is pressurized open the valve completely.
- Functional testing: Test the function of the inflator and the dump valves of your BCD. Take some breaths from your main second stage while looking at the SPG. If breathing is easy and comfortable and the needle of the SPG stays steady your regulator is in working order. Repeat this with all second stages of your regulators. Confirm on the SPG that you have sufficient air supply for the planned dive. Attach the octopus to the bracket provided. Finally, listen for air leakages.
- Stow safely: If you leave your scuba set unattended, lay it on the floor with all hoses tagged inside the BCD. Never leave your scuba set or a diving cylinder standing upright while unattended. If stowed on a boat, make sure it cannot role around and second stages are secured in brackets provided on the BCD.
- Wearing the scuba set: Since a scuba gear is quite heavy, it is good practice to help each other in putting it on the back. Your VIT instructor will show you various ways without hurting your back.
After the dive you have to disassemble the scuba set again:
- Close valve: First add some air to the BCD with the inflator and then close the cylinder valves.
- Depressurize regulator: Press the purge button on your second stages until the system is completely depressurized. If there is still some remaining pressure you are not able to unscrew the first stage from the cylinder valve.
- Remove regulator: Disconnect the inflator hose from the inflator and unscrew the regulator from the cylinder valve. Dry the protective cap and attach it to the high pressure inlet of the regulator.
- Remove BCD: Open the tank strap and remove the BCD from the diving cylinder.
- Drain BCD: Some water may have accumulated inside the BCD. Turn it over, hold the inflator down and drain the water with the inflator's purge button.
- Stow safely: Lay the diving cylinder on the floor or place it into an existing bracket. Make sure that neither dirt nor water can get into the valve opening. Stow away BCD and regulator. Make sure that the hoses are not kinked.
- Cleaning and care: Pay attention to the care instructions in the articles BCD and Regulator.