Scuba diving is one of the few sports that requires a consumable item before participating--compressed air. Although most divers get their tanks filled at low cost at their local dive shop, some experienced divers choose to invest in the right equipment to routinely fill their scuba tanks at home.
Empty your scuba tank so that 2.27 to 4.54 Kilogram of air per square inch remain, by connecting a regulator to it and purging air until the pressure gauge reaches the target level. Shake the tank a bit to assess for water or foreign objects--if any are detected, take the tank to a dive shop for a full inspection and repair.
Prepare the scuba tank compressor for use. Compressors come in many different models and sizes, so check the documentation for a checklist of specific steps to take before use, including lubricating pistons, replacing filters or checking hoses.
Attach the cylinder to the compressor--typically, by screwing the main lead from the compressor to the valve of the tank. Make sure all valves, yokes and hoses are properly seated and tightened, and wipe away any excess debris or moisture. Ensure that the tank valve is open.
Begin the fill cycle according to the compressor's instructions. Do not overfill the tank past the capacity stamped on the tank.
When the tank is full, close the cylinder valve and remove all hoses. Secure the compressor according to the manufacturer's instructions, then inspect the tank for the hiss of escaping air or signs of cracks in the metal. Put the dust cap over the tank's screw threads, as a safety precaution.
Use a dive shop to get enriched air mixtures, to ensure safety. Follow normal safety protocols and get your tanks inspected annually by a certified dive equipment technician, through your local dive shop. Get certified in equipment repair and visual tank inspection; some dive shops and equipment vendors may not sell compressors to non-certified buyers.
Never use an ordinary air compressor to attempt to fill a scuba cylinder--impurities in the air can be lethal when inhaled under pressure. In some places, it is illegal to fill others' tanks without professional certification. Ensure that the filling process is monitored at all times--a damaged tank or improperly set auto-shutoff can lead to catastrophic failure, causing serious injury and property damage.