Author: PierLuigi Da Rolt
There are three types of hands that a diver uses or has used in his career: pressure gauges, depth gauges, and compasses. Although electronics dominate the world of diving instruments these days, the continued validity of these instruments in their analog configuration remains undeniable.
But how much we breathe.
In the past, pressure gauges weren't used in scuba diving; a diver couldn't know, in real time, how much gas their tanks contained. The only safety device was a so-called "reserve" valve, located on the valve itself, which, at a pressure of 50 bar, shut off the air flow. To breathe again, the diver had to pull a rod located next to the tanks, which reopened the valve. At that point, the diver knew he still had 50 bar available for ascent.
With the advent and use of the pressure gauge, things have changed radically and every diver knows perfectly well, at any moment during the dive, how much pressure and consequently how much gas and how much autonomy he has left.
But how are these precious instruments made?
We all know it from the outside: a dial with a scale and a hand controlled by an internal mechanism that indicates the pressure in the tanks. The dial usually indicates, in red, the 50 BAR zone, the reserve that the diver, if he or she has planned their dive well, should still have in the tank when exiting the water. The full scale can be 200, 300, or even 400 BAR depending on the pressure the instrument can handle. But why such high pressures if most tanks cannot be filled to pressures above 200 BAR? Nowadays, many manufacturers market tanks with operating pressures much higher than 200 BAR, and furthermore, pressure gauges with a wider full scale have proven to be more precise and reliable. This feature is particularly appreciated by Tek Divers.
The internal mechanism that moves the needle can be one of two types: spring-loaded or Bourdon tube-loaded. The operating principle is nearly identical and relies on a small tube that is deformed by the gas pressure coming from the connecting hose to the first stage. Spring-loaded pressure gauges can easily be distinguished from those with a Bourdon tube. Simply hold the instrument in one hand and tap it lightly on the side of the palm of your other hand. If the needle vibrates slightly, the internal mechanism is definitely spring-loaded.
Some commercially available analog pressure gauges contain a liquid inside them, usually glycyrena oil. This feature, given the incompressibility of the liquid, makes the instrument immune to implosions caused by depth and high pressure. In particularly deep dives, the pressure is so strong that it crushes the glass, which in turn causes the needle to become stuck at a completely false pressure value.
Electronics have also arrived in this category of instruments, and many digital pressure gauges are now available on the market. These latest-generation instruments can be divided into two main families: those connected to the first stage by the traditional high-pressure hose, and those equipped with a transmitter, a special probe attached to the HP port of the first stage that transmits pressure data to the instrument via waves.
Digital pressure gauges have the ability, through appropriate algorithms, not only to indicate the quantity of gas present in the cylinders, but also to calculate the remaining autonomy time, situations of respiratory distress and therefore any abnormal consumption.
As mentioned above, digital pressure gauges can be equipped with a HP hose or a data transmitter. Almost all models are integrated with a dive computer, which can be a significant factor in choosing one product over another. If the instrument is of the hose type, the diver will be forced to have the computer on the console, while, in the latter case, the pressure gauge will be integrated into a wrist computer.
The depth.
For a diver, knowing your depth is of primary importance at all times. Hence the need for a device that can indicate it at all times: a depth gauge. Although modern computers, with their current and maximum depth displays, dominate today, simple depth gauges have certainly not lost their usefulness. Many divers always carry one, either in their BCD pocket or on their wrist; it's an excellent backup solution in the unfortunate event of a computer failure.
Analog depth gauges consist of a dial with a depth scale ranging from 0 to a certain number of meters. On this dial, the current and maximum depths are indicated by two hands: the first, usually black, indicates the current depth, while the second, usually red, indicates the maximum depth reached. The depth scale should be clearly legible and suitably spaced; this is essential for decompression depths of 12, 9, 6, and 3 meters. The further apart the scale is, the easier it will be to maintain a precise depth. Some models feature a rotating glass, and with it the depth hand. This system allows the hand to be set precisely to zero if the instrument is not self-compensating and therefore sensitive to small atmospheric variations. An important tip is to also reset the maximum depth hand before diving, as it will certainly still indicate the maximum depth reached during the previous dive.
Analog depth gauges essentially fall into two types: oil-filled and diaphragm. The former, as the name suggests, have the entire case, including the internal mechanism and dial, filled with oil; ambient pressure is then transmitted by the liquid to the sensing mechanism. In the latter, however, pressure differences are transmitted by a diaphragm located on the instrument's case.
There is also a lesser-known instrument that lacks hands: the water column depth gauge. Its operation is very simple: it has a dial with meters indicated (usually the full scale does not exceed 15 meters for accuracy reasons). On the outside of the dial is a small tube with a hole at the zero mark.
During descent, water will enter the tube, forming a column of water that will advance proportionally to the ambient pressure. The water level inside the tube will indicate, on the dial, the diver's depth. As you ascend, the reverse occurs. A characteristic of this type of instrument is a loss of accuracy at significant depths, but for minimal depths, say within 12 meters, and especially during classic decompression stops, its accuracy is more than acceptable. An advantage of this type of instrument is its particular sensitivity not only to water pressure but also to atmospheric pressure. Remember that the conventional atmospheric pressure of 1 ATM is relative to sea level, but that if you move to a higher altitude, this value will be proportionally lower. This feature can prove useful during high-altitude dives, where traditional analog depth gauges lose some of their accuracy. Water column depth gauges are not currently suitable for diving; their use depends on pairing with a more comprehensive instrument. For example, a water column depth gauge does not store, and therefore does not provide its user with, the maximum depth reached during a dive.
Digital or electronic depth gauges also exist. These instruments typically include a timer that stores dive times. They also display a wide range of data, including depth and time, as already mentioned, including the maximum depth reached, ascent rate with an alarm when the maximum depth is exceeded, and water temperature. They also store a certain number of dives in their memory. A small drawback, compared to analog gauges, is their slower response time, meaning the time between a change in depth and the instrument's reaction. A hand-based depth gauge will indicate any change in depth in real time, while a digital one undoubtedly has a slower response time.
The compass, this unknown.
When diving, it's not always possible to rely on natural landmarks, such as walls, landslides, and the like, to safely return to the starting point. Hence the need for instrumental orientation. Too many divers still lack in-depth knowledge of the use of a compass, either because they are accompanied on their dives, or because they have always conducted them in familiar locations, with good visibility and, in any case, with valid natural landmarks. The usefulness of this instrument, however, should not be underestimated, and its use, if properly learned, is far from difficult. Of course, an underwater compass cannot be used for very complicated navigation; let's say that the accuracy of a round trip on the same route or a route followed in a square or rake pattern is acceptable.
Underwater compasses function similarly to land compasses; they have a round dial similar to a protractor, divided into degrees from 0 to 360. Inside, a magnetic needle is fixed to a central pivot, always pointing toward magnetic north. It's called magnetic north because, in almost all cases, magnetic north doesn't correspond to true north. These inaccuracies are caused by interference with Earth's magnetism, such as the presence of significant ferrous masses or sources of electromagnetism. But this doesn't matter to the diver; the magnetic needle is merely a fixed point used to determine the direction you're taking relative to your starting point. However, this doesn't mean that an underwater compass is free from complications caused by the attraction of metals; it's important to remember that much scuba equipment is made of metal, and that tanks, for example, have considerable mass. To avoid navigation errors, it is good practice for the diver to orient himself and take compass bearings after putting on all his equipment, even better if this operation is carried out immediately before the dive.
There are various types of compasses on the market, from the smallest ones that can be attached to a watch strap to the bulkier ones that take up as much space as any other diving instrument, whether worn on a console or on the wrist. Many models feature a rotating bezel above the dial, usually featuring graduations, but more importantly, two diametrically opposed notches and a central line known as the "lubber line." The notches essentially serve to remember the position and keep the needle at a certain point on the dial so as to be able to follow a certain course, while the lubber line is simply the ideal perpendicular line of the diver's body. Other models feature a side window that displays the degrees on the dial. This reading system allows the compass to be positioned precisely in front of the diver's eyes and, by holding the arms in a certain way, to be able to maintain a perhaps better course than if one were to follow the lubber line, i.e., reading the compass from above. Another characteristic of most compasses is that, when consulting them, they must be kept as horizontal as possible. The goal is to prevent the needle, which is obviously tilting because it's mounted on a pivot, from touching any internal part of the case. If the needle were to touch it, it would be blocked, resulting in an incorrect heading reading.
As with pressure gauges and depth gauges, electronics have also been making their appearance in this type of instrument for a few years now. Many manufacturers now include digital compasses in their catalogs. These instruments have many advantages, and they greatly facilitate navigation. Some can store previous routes taken during the same dive, in case the diver briefly considers changing direction. Still others can automatically calculate and indicate the return route, either following the exact same path as the outward journey, or even taking the shortest route.
A quick tip: don't forget that compasses are magnetic instruments, so it's best to keep them separate from strong sources of electromagnetism, such as cell phones. Cell phones should also be kept away from dive computers.
These are magnificent tools, therefore, useful for increasing the safety of any dive and making other dives possible. They are tools that all divers should know, and it's absolutely worth learning how to use them properly by taking an underwater navigation course.
PierLuigi Da Rolt (OLDSHARK)
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