Equipment Flashcards
What markings should tanks have?
Max working pressure
Material
Hydrostatic/ pressure test date
Steel tank description and advantages
Round base
Normal working pressure of 220 bar
More negatively buoyant (better for cold water with dry suits)
When pressure drops, buoyancy of diver isn’t affected
Aluminium tank description and advantages
Flat bottom
220 bar working pressure
Last longer and easier to clean as produce aluminium oxide instead of rust
Can use with higher working pressures
More buoyant - when pressure drops, diver needs to add more weight
Visual inspection
Recommended once a year for steel and aluminium
Looks for corrosion inside tanks
Checks threading at neck of tank
Hydrostatic testing
Every 5 years in US, every 4 years in UK
Tank is pressurised to 7/5 it’s working pressure and then checked for damage
When should a hydrostatic test be done before it’s due date?
After tank is exposed to these conditions:
Tumbling or sandblasting to remove corrosion
Damage due to impact
Temperatures above 82C
K valves
Normal valve on tank that will open or close allowing the tank pressure out of the tank
Fitted with a DIN or yoke valve for attachment to the first stage
DIN screws in to K valve
What is a burst disc?
Thin copper disc that will break if the pressure in the tank is too high
Instead of exploding, the air will come out of the burst disc
J valve
Also called reserve valve - used before pressure gauges came into use
Spring loaded valve that shuts off when pressure gets low - the diver could then reach back and pull a pin to reopen it, but would know they have a reserve amount of air left
When filling the pin needs to be in down position
Purpose of first stage
Reduces pressure to intermediate pressure (9-13 bar) through low pressure hoses
Guides high pressure air to gauge
Balances vs unbalanced regs
Unbalanced - tank pressure resists and assists the opening and closing of valve in the first stage, directly affecting breathing resistance due to pressure, air in tank or use of AS
Balanced - neither resist nor assist so supply s constant resistance
How does the 2nd stage work?
As diver breathes, diaphragm moves inwards and presses down on a lever, moving the valve and allowing the air in the low pressure hose to enter
What is the downstream valve?
Opens with the flow of air (valve in the 2nd stage)
What is the upstream valve?
Valve in 2nd stage that opens against the flow of air
What is a fail safe valve?
If valve fails it will remain in the open position causing a free flow
What is environmental sealing?
Seal of silicone or grease around the first stage to stop it freezing in cold waters
Capillary depth gauges
Simple piece of clear tubing, closed at one end and open at the other
Work using Boyles law
Hard to read accurately
Open bourdon tube gauges
Spiral shaped tube
Water enters one end - increasing pressure causes tube to straighten which causes needle to move
As it is open it is liable to clogging
Oil filled gauges
Use bourdon tube design but using a sealed tube in an oil filled gauge housing
Pressure increasing causes the tube to coil more tightly which moves the needle
Doesn’t clog as is sealed
Diaphragm gauges
Connect a flexible diaphragm to levers and gears that move the needle
Digital gauges
Measure pressure using a transducer which varies the electricity it transmits depending on the pressure
SPG
Work on same principle as bourdon tube gauges
What are the industry guidelines to do with nitrox cylinders?
Must be O2 cleaned if using more than 23%
Must be cleaned and lubricated specially if using more than 40% (40% rule) and must be cleaned again if filled using a normal air source
EAN cylinder markings
15cm band at tank shoulder - top and bottom should be yellow 2.5cm band with centre section green + labelled EAN
Visual inspection sticker
Label with current blend, fill date, MOD of current blend and analyser name
How much weight needs a lifting bag?
4-7kg
How do you measure distance?
Arm spans
What way do the currents flow globally?
Northern hemisphere - clockwise
Southern Hemisphere - anti-clockwise
Why do waves break?
Bottom topography
Describe a DIN valve
Screws in
Allows higher pressure
How does an SPG work?
C shaped or spiral tube that straightens causing needle to move
3rd method taught for out of air situation in OWC
CESA
Jellyfish sting treatment
Vinegar
Rubbing alcohol
Diluted household ammonia
