Bottles & Stock

Άρθρο: Γιώργος Πέτρου

Photo: George Petrou, Vasilis Petroulias & Greek Diver archive

Calculating the gas reserve and choosing the volume/pressure of our cylinder always remains a topical and very useful topic.

No one wants to experience an air shortage incident.

Let's make it clear that for someone to "stay" out of the air means that they have committed many serious mistakes in terms of mentality and security measures, violating many rules.

Ας πούμε κάποια λίγα βασικά στοιχεία επί του θέματος.

Pressure-Volume of bottles

We all know that there are bottle volumes such as 2, 3, 6, 10, 12, 15, 18, 20 liters.

This tank volume is ideal to support dives from simple amateur to specialized forms of technical diving.

In the table below, we will see, by filling these bottles with a specific pressure, their capacity in liters.

First of all, let's remember that when we say that a bottle has a volume of 10 liters (at 1 ata pressure F/S=P) we mean that if I fill it with water, it will hold 10 liters of water.

➥ How do I calculate how much gas is required for a dive?

Τα στοιχεία τα οποία απαιτούνται για να υπολογίσω το πόσο αέριο απαιτείται για μια κατάδυση είναι:

■ Gas quantity for the cathode

■ Amount of gas for stay

■ Amount of gas for ascent

■ Amount of gas for decompression

■ Gas quantity for reserve (reserve)

• Αστάθμητο παράγοντα

Cylinder volume (liters) X Filling pressure (Bar) = Liters of gas in capacity. This is the relationship we are interested in.

The cylinders are filled (filled) from 200 to 300 bar.

In terms of materials, it can be made of steel, aluminum and kevlar. Each material has its positive and negative characteristics.

Filling examples of pressure volume ratio liters capacity

10 liter Χ 200 bar = 2000 liter. 10 liter X 300 bar = 3000 liter 2 φιάλες Χ10 liter X 200 bar = 4000 liter

12 X 200 bar =  2400 litr

15 x 200 bar = 3000 liters

18 X 200 bar = 3600

The formula we use to calculate the required volume of gas for a dive is: P x T x SCR x MOD.

To this, a reserve law such as 1/3 (with or without the MOD) can be added, etc.

Where:

P Pressure = Absolute depth pressure

Τ Time = Χρόνος

SCR Surface Consumption Rate = Surface Consumption Rate

MOD Modifiers = Project Production Factors

➥ What criteria will I use to decide how much gas to stock?

Κριτήρια / στοιχεία είναι:

● The depth we will dive to in combination with the dive time and the required ascent time.

Caution: If 50 bar may be enough to cover our needs, one ascent and one mandatory preventive decompression for a dive to a depth of 18 meters for some time, if we dive deeper it will definitely not be enough.

● Ο χρόνος αποσυμπίεσης σε συνδυασμό με το βάθος που γίνεται αυτός.

● The possible unmeasured factors that can be presented as:

- Hypothermia increases the rate of consumption.

- Hypercapnia - Tachypnea - increased CO2 (Carbon Dioxide)

- Does our stock cover the case that our couple experiences a gas shortage and requests support from us?

Το απόθεμά μας μειώνεται στο ήμισυ και το άγχος ανεβαίνει αυξάνοντας το ρυθμό κατανάλωσής μας.

- The production of work, for example like swimming against a strong current.

- Gas loss from a leak in the pressure regulator, buoyancy regulator or from a valve, etc.

- Exceeding the plan and increasing the mandatory decompression time.

- Λάθος ένδειξη στο μανόμετρο....

- Καταδύομαι με αέρα και έχω να πραγματοποιήσω μια αποσυμπίεση π.χ. 3 λεπτά στα 6 μέτρα και 10 λεπτά στα 3 μέτρα με ένα Enriched Air Nitrox 32. Ξαφνικά για κάποιο λόγο δεν μπορώ να χρησιμοποιήσω τη φιάλη αυτή. Τώρα την αποσυμπίεση πρέπει να την κάνω με τον αέρα. Αναπόφευκτα έχουμε αύξηση χρόνου αποσυμπίεσης. Έχουμε άραγε υπολογίσει το απαραίτητο απόθεμα ή αερίου του αέρα;

➥ Is there an easy way to calculate what size tank I need, knowing how much gas I will need for a dive?

ensuring the necessary stock?

Let's assume that for a dive we need 2000 liters of gas e.g. 70 bar of gas as a reserve.

To see what volume of bottle we will need, we do the very simple thing:

We divide the total gas volume by the filling pressure of our cylinder, subtracting the pressure of the reserve we desire.

Παράδειγμα:

2000 liters / (200 bar – 70 bar reserve) = 2000 liters / 130 bar = 15 liters (15.384 to be exact)

Άρα μόλις εγώ χρησιμοποιήσω τα 2000 λίτρα θα έχω ένα απόθεμα 70 bar το οποίο μεταφράζεται σε 70 bar x 15 λίτρα φιάλη = 1050 λίτρα

The correct mentality of always surfacing with a reserve of at least 50 bar on the surface is lifesaving.

➥ The main question I need to answer is:

What is the minimum pressure at which I should begin my ascent and with how many bars should I begin my ascent so that I have a safety margin on the surface of at least 50 bars?

We will answer this in another article. The fact is that the deeper I dive in combination with time, the greater my reserve must be. The above is only a superficial reference to the subject.

For complete knowledge of this, attending school with a certified instructor is required.

■ For any questions

contact George Petrou,

georgedpetrou@gmail.com