Chapter 1 - The Aqualung And Equipment

Question 1

How many bars of pressure does an air cylinder usually contain?

Answer 1

232 bars

Question 2

What are the two types of cylinder construction?

Answer 2

Steel - BS 5045/7 - 4-5mm - drawing and spinning - strong and thinner

Aluminium - BS 5045/8 - 11mm - extrusion and forming - resistant to corrosion - thicker

Question 3

Which cylinder is more buoyant?

Answer 3

Aluminium - displaces more is water - divers have to add more weight approx 2 kg

Question 4

What markings do you need on a cylinder?

Answer 4

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

Question 5

What are the standards of testing for cylinders?

Answer 5

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

Question 6

What do the HSE recommend for colour coding cylinders?

Answer 6

Black / white band - breathing air and must also be clearly labelled

Blue neck - nitrox - must be marked with a maximum operating depth

Question 7

What must happen if nitrox percentages are greater than 25%?

Answer 7

Must be O2 cleaned and serviced

Question 8

What are the characteristics of the cylinder valve?

Answer 8

Crossflow to avoid stiffness when turning the valve knob

Anti debris tube so dust doesn’t get into the regulator

Question 9

Which clamp is the safest out of don and A clamp and why?

Answer 9

DIN are safer - they actually screw into the cylinder valve trapping the high pressure o ring

Question 10

What are the 2 types of din fittings?

Answer 10

Din 200 - 5 threads - 232 bar

Din 300 - 7 threads - 300 bar

Question 11

What is the cylinder user maintenance?

Answer 11

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

Question 12

What is the use of the first stage of the regulator?

Answer 12

Connects to cylinder - accepts high pressure and reduces it to 8-12 bar above ambient pressure (interstate/intermediate pressure)

Question 13

What does the second stage of the regulator do?

Answer 13

Reduces the air to ambient pressure for the diver. Also known as the demand valve.

Question 14

What are the main two types of first stage?

Answer 14

Diaphragm and piston

Question 15

How does the diaphragm first stage work?

Answer 15

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

Question 16

How does the piston first stage work?

Answer 16

Operated by main piston
Water enters the main body of the first stage
Environmentally sealed to reduce freezing

Question 17

What are HP restrictors?

Answer 17

3 different types but all restrict the flow of high pressure gas going to the HP hose and gauge.

Question 18

What’s the difference between balanced and unbalanced first stages?

Answer 18

Balanced - breathe easier, more capable of supplying air, better for 2 divers, unaffected by change in cylinder pressure

Unbalanced- increased effort to breathe

Question 19

What’s the difference between downstream and upstream valves?

Answer 19

Downstream valves - if 2nd stage fails air flows

Upstream valves - if 2nd stage fails air stops

Question 20

What are the three types of BCD?

Answer 20

Stabiliser jackets or adjustable diving vests
Wing
Drysuit

Question 21

What is the typical volume of BCDs?

Answer 21

14-22 litres

Question 22

How do stabiliser jackets(stabs) work?

Answer 22

Waistcoat attaches to cylinder
Comfortable 
May have an additional second stage
Provides additional source of air
Adjustable
May have an integral weight system

Question 23

How do wings work?

Answer 23

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

Question 24

How does the secondary air supply (pony/bailout) work?

Answer 24

Small cylinder attached to main cylinder
3-5L
Carry emergency air

Question 25

How does the spare air cylinder work?

Answer 25

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

Question 26

How to twin set cylinders work?

Answer 26

Two cylinders on the same harness
Military divers - cylinders connected with a manifold
Cave divers - cylinders are completely separate

Question 27

What is the rule of thirds?

Answer 27

1/3 air - descent to half way turn point
1/3 air - second half of dive and ascent
1/3 air - backup

Question 28

What are the types of depth gauges?

Answer 28

Bourdon tube gauge
Diaphragm gauge
Capillary gauge

Question 29

How do SMBs work?

Answer 29

Minimum 10kg buoyancy float
Display the A flag
1-2mm nylon line
1.25x max depth

Question 30

Why do we need diving suits?

Answer 30

The human body can’t contain heat in water cooler than 23°

Water conducts heat away from the body 25x faster than air

Question 31

When do we wear wetsuits?

Answer 31

Water warmer than 15°

Should be close fitting

Question 32

What is neoprene vulnerable to?

Answer 32

Sunlight, oils and solvents

Question 33

What happens if you turn the rotating cap on a drysuit clockwise?

Answer 33

It increases the spring load and allows a larger volume/pressure of air to be maintained in the drysuit

Question 34

How can you escape from inverted legs at the surface in a drysuit?

Answer 34

Inflate the BCD and possibly use ankle weights

Question 35

How do you escape inversion underwater?

Answer 35

Jack knifing the legs
Forward roll
Ankle weights may help