page_title: Diving air compressor
section_title: Gas blending
hierarchical_section_title: Diving air compressor / Gas blending
caption_attribution_description: English: I photographed this myself
context_page_description: A diving air compressor is a gas compressor that can provide breathing air directly to a surface-supplied diver, or fill diving cylinders with high-pressure air pure enough to be used as a breathing gas.
  A low pressure diving air compressor usually has a delivery pressure of up to 30 bar, which is regulated to suit the depth of the dive.
  A high pressure diving compressor has a delivery pressure which is usually over 150 bar, and is commonly between 200 and 300 bar. The pressure is limited by an overpressure valve which may be adjustable.
context_section_description: Compressors may be linked to a gas blending panel to  make nitrox, trimix, heliair or heliox mixes. The panel controls the decanting of oxygen and helium from cylinders bought from commercial gas suppliers.
  As it is not possible to decant to a diving cylinder from a storage cylinder that holds gas at a lower pressure than the diving cylinder, the expensive gas in low pressure storage cylinders is not easily consumed and may go to waste when the storage cylinder is returned to the supplier. The cascade system may be used with a bank of storage cylinders to economically consume these high cost gases so that the economically maximum gas is used from the bank. This involves filling a diving cylinder by first decanting from the bank cylinder with the lowest pressure that is higher than the diving cylinder's pressure and then from the next higher-pressure bank cylinder in succession until the diving cylinder is full. The system maximizes the use of low-pressure bank gas and minimizes the use of high-pressure bank gas.
  Another method for scavenging expensive low pressure gases is to pump it with a gas booster pump such as a Haskel pump, or to add it to the intake air of a suitable compressor at atmospheric pressure in a mixer known as a blending stick.
caption: Gas blending panel
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