13/20
GENERAL INFORMATION (CON’T)
TEST
Note down the following:
•
The ambient temperature,
•
The atmospheric pressure,
•
The buoyancy tube pressure (240/250mbar) with the Zodiac pressure gauge.
TEST DURATION : 24:00 hours minimum
As specified in I.S.O 6185, authorized pressure drop is 20% in 24 hours.
For buoyancy tubes whose operating pressure is 240 Mbar, Zodiac allows the following tolerances.
Boats between 0 & 1 year
12,5% or 30 Mbar
Per 24 hours
Boats between 1 & 2 years
15% or 36 Mbar
Per 24 hours
Boats 2 years old & more
20% or 48 Mbar
Per 24 hours
CORRECTED PRESSURE TEST :
FORMULA = 1° Celsius = (+/-) 4 mbar.
a) The principle of corrected pressure test:
Take the above law of physics and turn it into a formula. This is how it works:
In an airtight buoyancy tube when temperatures rise, air expands, thus increasing its pressure. On the
other hand and in the same buoyancy tube, when temperatures fall, so does the pressure, as the air
contracts in the same given volume, and therefore pressure decreases.
A “corrected” pressure reading will calculate the amount of pressure that rose or fell due to a
temperature variation during the test. To find this number, one must register the temperature, in
Celsius, at the beginning and at the end of a pressure test.
This difference will be multiplied by 4 and will be added to, or subtracted from the pressure drop as
read on the pressure gauge.
If the temperature drops during your pressure test, you will add that amount to the pressure loss you
registered on the pressure gauge, as really, part of that pressure loss is due to the “shrinkage” of air
as a result of a temperature drop. On the other hand, if the pressure rises, you will subtract that
amount as the air expanded and you should compensate (by subtracting it) from your pressure gauge
reading.
If during the test the temperature remains constant, you will not have to subtract, or add, as the
temperature has remained constant, and in this case, your pressure loss read on the pressure gauge
is your real pressure loss.
b) Examples of corrected pressure tests:
First Example: When temperatures drop:
Date
Time
Pressure Temp
Jan 01
16:00
240 mbar 20°C
Jan 02
16:00
210 mbar 15°C
Difference
24hrs
30 mbar
- 5°C x 4 = +20 (when temperature drops: add!)
Result
210 mbar
+20
= 230 mbar
Corrected Pressure =240 mbar - 230 = 10 mbar: boat passes test!
When the temperature drops, you add the amount of the corrected temperature to the amount
of your pressure difference.