Significance

• The compressor generates warm air, which temporarily increases the internal pressure. Each scuba tank is rated with a maximum working pressure, which is higher than its holding capacity, in order to safely accommodate increased pressure air during fills.
  
  

Function

• If the tank pressure exceeds the maximum working pressure, a safety (burst) valve will release air. The tank pressure will normalize as the air and tank cool to room temperature, allowing divers and operators to accurately check air pressure.
  
  

Features

• Many dive operators incorporate a cooling water bath to quickly rinse and cool the tank during filling. This preference reduces waiting time to add air so that the tank is filled to capacity (top off).
  
  

Expert Insight

• According to SanDiegoDiving, the maximum rate recommended to fill scuba tanks is 300 psi/minute to avoid damaging the cylinder. A cooling water bath is not recommended because this may introduce water into the compressor system or into the tank, causing corrosion.
  
  

Considerations

• Many divers are in a rush to fill tanks so that they can get back into the water quickly. A hot fill can produce a short fill or over-pressurized tank, so it is prudent to wait for a tank to be filled, cooled and topped off to the appropriate pressure.