Chapter 1 - The Aqualung And Equipment Flashcards
How many bars of pressure does an air cylinder usually contain?
232 bars
What are the two types of cylinder construction?
Steel - BS 5045/7 - 4-5mm - drawing and spinning - strong and thinner
Aluminium - BS 5045/8 - 11mm - extrusion and forming - resistant to corrosion - thicker
Which cylinder is more buoyant?
Aluminium - displaces more is water - divers have to add more weight approx 2 kg
What markings do you need on a cylinder?
Manufacturing name Mark Date Serial number Specification - material Weight Water capacity Pressure at test Working pressure/charging pressure - 207/232/300 Periodic inspection test CE mark IDEST
What are the standards of testing for cylinders?
Externally - within 6 hours before use by a competent person
Internally - every 2.5 years by a competent person - visual inspection
Internally - every 5 years by an overpressure test
What do the HSE recommend for colour coding cylinders?
Black / white band - breathing air and must also be clearly labelled
Blue neck - nitrox - must be marked with a maximum operating depth
What must happen if nitrox percentages are greater than 25%?
Must be O2 cleaned and serviced
What are the characteristics of the cylinder valve?
Crossflow to avoid stiffness when turning the valve knob
Anti debris tube so dust doesn’t get into the regulator
Which clamp is the safest out of don and A clamp and why?
DIN are safer - they actually screw into the cylinder valve trapping the high pressure o ring
What are the 2 types of din fittings?
Din 200 - 5 threads - 232 bar
Din 300 - 7 threads - 300 bar
What is the cylinder user maintenance?
Rinse with fresh water post use Paint Prevent digs / scratches to exterior Never store empty - allows moisture into the cylinder and can cause rust Never store full - ideally >50 bar
What is the use of the first stage of the regulator?
Connects to cylinder - accepts high pressure and reduces it to 8-12 bar above ambient pressure (interstate/intermediate pressure)
What does the second stage of the regulator do?
Reduces the air to ambient pressure for the diver. Also known as the demand valve.
What are the main two types of first stage?
Diaphragm and piston
How does the diaphragm first stage work?
Operates by water pressure acting on the diaphragm, supplemented by a force exerted by the main spring.
Insulated type - no water enters the main body - reduces freezing
How does the piston first stage work?
Operated by main piston
Water enters the main body of the first stage
Environmentally sealed to reduce freezing
What are HP restrictors?
3 different types but all restrict the flow of high pressure gas going to the HP hose and gauge.
What’s the difference between balanced and unbalanced first stages?
Balanced - breathe easier, more capable of supplying air, better for 2 divers, unaffected by change in cylinder pressure
Unbalanced- increased effort to breathe
What’s the difference between downstream and upstream valves?
Downstream valves - if 2nd stage fails air flows
Upstream valves - if 2nd stage fails air stops
What are the three types of BCD?
Stabiliser jackets or adjustable diving vests
Wing
Drysuit
What is the typical volume of BCDs?
14-22 litres
How do stabiliser jackets(stabs) work?
Waistcoat attaches to cylinder Comfortable May have an additional second stage Provides additional source of air Adjustable May have an integral weight system
How do wings work?
Inflatable buoyancy bladder
Large volume for increased buoyancy
Wing remains on divers back freeing the front and sides
May not support diver in the face up position
How does the secondary air supply (pony/bailout) work?
Small cylinder attached to main cylinder
3-5L
Carry emergency air
How does the spare air cylinder work?
0.5L charged to 232 bars
Breathe directly from cylinder
116 L available if cylinder is fully charged
Not enough to make a safe ascent - 2 mins at 10 m
How to twin set cylinders work?
Two cylinders on the same harness
Military divers - cylinders connected with a manifold
Cave divers - cylinders are completely separate
What is the rule of thirds?
1/3 air - descent to half way turn point
1/3 air - second half of dive and ascent
1/3 air - backup
What are the types of depth gauges?
Bourdon tube gauge
Diaphragm gauge
Capillary gauge
How do SMBs work?
Minimum 10kg buoyancy float
Display the A flag
1-2mm nylon line
1.25x max depth
Why do we need diving suits?
The human body can’t contain heat in water cooler than 23°
Water conducts heat away from the body 25x faster than air
When do we wear wetsuits?
Water warmer than 15°
Should be close fitting
What is neoprene vulnerable to?
Sunlight, oils and solvents
What happens if you turn the rotating cap on a drysuit clockwise?
It increases the spring load and allows a larger volume/pressure of air to be maintained in the drysuit
How can you escape from inverted legs at the surface in a drysuit?
Inflate the BCD and possibly use ankle weights
How do you escape inversion underwater?
Jack knifing the legs
Forward roll
Ankle weights may help
