Diving Air Compressors for Scuba Diving 

Individuals engaged in scuba diving span the spectrum from the professional that is diving and using equipment on a daily basis to the recreational that only uses equipment once a year while on holiday. Whether professional or recreational, the quality and purity of the air that is provided by the cylinder are still as important. This in turn is dependent on the quality of the compressor package that is used to charge the cylinders. 

High Pressure Diving Air Compressors

Scuba diving cylinders are high pressure containers that can hold air at pressures in the range of ~ 150 to ~ 300 bar. To charge cylinders at this pressure requires special high pressure multi-stage reciprocating compressors which can come with fixed or variable speed operation. They offer a defined high pressure output with a certain volumetric flow that can rapidly charge scuba diving cylinders.

 

A schematic for a Reavell air compressor block that is typically used in the MAKO product range is shown below. This reciprocating four-stage cylinder compressor is in a “V” configuration and cooled by a large variable pitch fan. 


scuba diving
Reavell

In operation, air enters via the intake filter situated at the top and passes to the first stage where it is compressed before passing through a heat exchanger to the second stage. On exit from the second stage, it flows around a cooling system positioned in the fan air stream and then into a separator for condensate removal. On entering the third stage the air is further compressed before passing through the second cooling coil and condensate removal separator. Final compression takes place in the fourth stage before passing through a finned final cooling system. 


High pressure reciprocating compressors are typically provided with either an electrical or diesel engine drive set which both come with pros and potential cons. Electric motors offer the following potential advantages 

  • Quiet operation typically run much more quietly than diesel engine units 
  • Low maintenance require less servicing than engine counterparts 

However electric motors can also come with a number of potential disadvantages that can include: 

  • Limited portability the units need to be connected to a power source and as such not as mobile as an engine unit 
  • Potential size limitations – If you only have a single-phase electrical supply then you will typically be limited to units with 7.5kW (10HP) or less. 

While for Diesel engines, the potential advantages can include

  • Easy portability - Require no electrical connection and as such can move to different locations 
  • Greater availability - Depending on the location, diesel can be a more readily available and cost-effective option 

The disadvantages of diesel engines can include: 

  • Noise - Diesel engines are typically louder than electrical units 
  • Weight - They tend to be heavier which can somewhat impact their portability

Importance of air quality 

A high pressure diving air compressors deliver high-quality air at the desired pressure and volumetric flow. Reavell compressors are highly efficient and robust oil-lubricated compressors that when fitted into MAKO units come with purification filters that eliminate any potential contaminants. 
There are strict standards around the quality of air delivered by air compressors in the Scuba Diving arena. The CGA (Compressed Gas Association) Pamphlet G-7 is typically used for testing activity based out of America while the European standard EN 12021:2014 is generally used for testing in Europe. The table below completes s comparison and the two areas one might expect are similar, however, there are slight differences with the European standard being more stringent on certain particulates. 

It is important that in selecting a high pressure air compressor package for Scuba Diving applications not only the pressure and charging rate are considered but also the quality and purity of the air that is going into the cylinders. 

Comparison of Scuba Diving Air standards in US and Europe

 

Potential contaminants

CGA Grade E

EN 12021:2014

 

Allowable limits

Allowable limits

Carbon Dioxide (CO2), ppm

1000

500

Carbon Monoxide (CO), ppm

10

5

Odour

No significant odour or taste

No significant odour or taste

Oil condensed (mg/m3)

5

0.5

% Oxygen

20 -22

20 – 22

Water ppm v/v

None Present

None present


en-HK