CYLINDER
The cylinder is the container that allows the diver to carry a reserve of breathable air underwater. The tank is made up of a bottle in steel or aluminium and a mechanism to regulate the airflow. The bottle is a cylindrical container, which has one closed end. The other end of the cylinder has a neck on it, which has a threaded hole, which allows a valve to be fitted for regulating the airflow. Generally it has a filling pressure of 232 atm. At the shoulder of the bottle all the details about the cylinder are printed, the volume, weight of the bottle, its number, the maximum pressure, test pressure, date of manufa
cture and the name of the manufacturer. Because of the material used the pressure to which they are exposed and environment in which they are used the cylinders are tested in authorised centers with a variable expiring date according to the rules of the different countries where they are used. The test consists of checking inside and outside for corrosion and pressure resistance test using pressure of 50% higher than in normal use. In the UK the first test is carried out 4 years after the date of construction and then after every two years. The date of testing is generally stamped under the manufacturing date, the cylinder, if made of steel is equipped with plastic support, which keep it upright. If it is in aluminium the bottom is already flat. An o-ring secures the sealing of the valves that is screwed to the bottle. For the assembly of regulator there are two types of fitting: DIN with five or seven thread female and INT with a yoke (A clamp). After diving the cylinder must be washed and stored in a dry place.
REGULATOR
This is what enables the diver to breathe underwater. This part the equipment allows air supply at ambient pressure.
At present most of the regulators available on the market are two—stage whereas the earliest ones were single-stage. Single stage regulators have single valve assemblies that reduces cylinder pressure to ambient pressure. Two stage regulators have a first stage that reduces cylinder pressure to ambient pressure plus a pre-set intermediate pressure and a second stage which reduces ambient plus intermediate pressure to simply ambient pressure. The first stages of the regulators can work with a piston or a diaphragm to reduce the cylinder pressure, and are normally with a balanced configuration, which allows better performance of the second stage.
ALTERNATIVE AIR SOURCE (Octopus)
Together with the main regulator it is advisable to have an alternative source of air in order to have a safer diving. This is an extra safety measure in case the main regulator stops functioning or if a buddy breathing needs to be carried out.
The A.A.S. is:A second stage or “Octopus” It is fixed to a low-pressure port of the first stage through a hose longer than the normal one. Its colour is different, generally yellow, so as it can be easily spotted. Spare regulator It consists of a complete regulator fixed to a second outlet valve of the tank. Even in this case the A.A.S. has an easily spotted colour.
Alternative air source inflators It consists of a B.C.D. inflator functioning as an octopus second stage by means of inflating low-pressure hose. (E.g. auto-air) Independent source It is possible to find on the market extra small cylinders of 0.5 or 1 lt., known as “Pony bottles”; these are equipped with an outlet valve that allows you to fix an extra regulator.
PRESSURE GAUGE
The pressure gauge is linked through a hose to the High Pressure (HP) of the first stage and shows the level of pressure in the cylinder, so that it can give a continual readout of the amount of air during diving. The pressure gauge must have a safety valve that will blow before the glass does, so that the glass will not explode into the face of a diver if there is a fault with the gauge.
BUOYANCY CONTROL DEVICE (B.C.D.)
The BCD is used to keep the buoyancy constant regardless of the changes in depths that occurs during diving. By inflating and deflating with the right amounts of air, changes in volume are compensated; this is due to the increase and decrease of pressure. It is fixed through one or two harness to the cylinder and has a soft or hard backpack.
The connection with the first stage of the regulator through a low-pressure hose allows the operation of inflating. Deflation can be carried out through a quick released valve or dump.
The BCD is also equipped with one or more valves to avoid the risks of over inflating it. The use of BCD on surface allows the diver to move and float freely.
DEPTH GAUGE
Depth gauge is an instrument that measures the depth during a dive. The instrument must always have a pointer that indicates the maximum depth reached during immersion as this data is fundamental when planning a dive with the dive tables. Digital depth gauges are available which beside the usual function of indicating the depth and the maximum depth can also indicate to the diver when the speeds of ascend exceed 10m/min. It can also indicate the temperature and the time of immersion. It can also calculate the surface interval and hold previous dives in its memory; this instrument is very useful because several functions are incorporated in one.
WATCH
Watch must be pressure and waterproof, it can be digital or analog. An external counter-clockwise rotating self-locking bezel is a must for registering elapsed time.
KNIFE
It is one of the most indispensable devices when diving because it gives some added safety in situations which could become critical, for example if one is caught in a net, especially when snorkelling. It can also be used for signalling by hitting the blade on the tank. It must be strong with a comfortable handle and well sharpened.
It must always be worn in handy position, knifes are generally worn on the inside of the calf, or on the upper arm. Knifes must be used only in case of real need, otherwise they could become blunt.
After use should be rinsed with fresh water dried and coated with oil.
SURFACE MARKER BUOY
A floating buoy is a piece of safety equipment that marks the presence of divers underwater. In some countries dive law requires flags. The buoy is topped with a blue and white flag known as an “A FLAG”. This flag “ALPHA” has an international definition of ”I HAVE DIVERS DOWN, KEEP WELL CLEAR AT SLOW SPEED”. You may also see a red flag and a white diagonal stripe on it.
DIVING TORCH
A torch can compensate the change in colours caused by the surrounding water.
There are different types from the smallest, which takes up a minimum space and fits into a B.C.D. pocket, to those much larger and much more powerful.
In Scuba diving torches with bigger and more powerful beams are used, which last a longer time. Some models can be equipped with rechargeable batteries that are very useful but may not last as long.
COMPASS
When diving without reference points and in reduced visibility, the compass supplies the diver with information of the route and helps with the return to the starting point. The most common compass has a window on one side to make it easy to read. It is normally worn on the wrist but can also be kept together with other instruments.
WHISTLE
A whistle is important because in an emergency it can signal the divers position over a great distance; it is advisable to be carried in a handy position.
BAG
Bags for every possible use are available on the market; it is worth looking at the size and strength of material, as they are never big enough. When on a boat or on a dinghy a fishnet bag is useful to keep personal belonging together and allow them to dry quicker.
KIT BOX
Parts of diving equipment consist of rubber or plastic material that in contact with a saline environment or when affected by the sun’s rays easily deteriorates. Therefore it is a good idea to keep a box handy with spare parts.
The followings are an example of what it should contain:
– a pair of straps for the fins
– a mask strap
– Snorkel fitting
– several o-rings
– a screwdriver
– a screw-spanner or multifunction tool
– a liquid neoprene tube
– a rope
