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In order to breathe air underwater, we compress air at high pressure inside a tank. Made of either aluminium or steel, in Japan all tanks require a hydrostatic (pressure-resistance) test every 3 years (for aluminium) or 5 years (for steel), based on the original manufacturing date.
Air is filled and used by way of a valve. The standard valve is now the K valve, but the J valve with a reserve lever is also used, if rarely, nowadays. When the air pressure in a tank using a J valve drops to below anywhere from 20-40 bar, the valve begins to close, increasing breathing resistance and one must manually pull a lever to restore air flow.
But with the widespread use of pressure gauges, the J valve is becoming an uncommon sight in diving.
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Tanks have rounded bottoms, so tank boots are used. In Japan, SCUBA tanks must be the colour grey by regulation. This colour varies internationally.
To prevent corrosion from moisture entering the tank, it is important to leave a reserve of 30 bar or so in your tank.To prevent any accidents, it is best to lay tanks flat in a cool area when not in use.
Steel tanks are heavier than aluminium tanks, so it is important to adjust your weights according to the type of tank used.
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Tanks
