Nitrox Made Easy: Which Nitrox system should I buy?
When deciding which Nitrox System to purchase there are a couple things you
might take into consideration to help you make the best decision:
- Initial system procurement cost
- Re-occurring cost per unit of Nitrox including maintenance, electricity
- Ease of system operation - effort and manpower required to operate
- Availability of oxygen
You can use this spreadsheet to understand the types of costs
associated with each of the different methods to make Nitrox.
Nitrox Cost Breakdown Spreadhseet
Here is an additional spreadsheet to help you understand what it costs to
fill a SCUBA tank at your shop.
Tank Fill Cost Spreadsheet
EnviroDive Services has an inexpensive downloadable
Blender Manual that has a wealth of information about Nitrox.
There are three major ways out there to make Nitrox. They are:
- Partial Pressure Blending (Enriched Air Nitrox - EANx)
- Nitrogen Separating Membrane (De Nitrogenated Air- DNAx)
- Continuous Gas Blending with the Nitrox Stik (also EANx)
There are advantages and disadvantages to each of the systems, here's a quick
rundown of their strengths and weaknesses:
Partial Pressure Blending:
Mixes pure oxygen directly into an empty and oxygen clean certified SCUBA
tank, then topped off with with Oxygen Compatible Air (OCA) from banks to create desired oxygen mixture.
Depending on the complexity of the blending station, you will spend a couple
thousand dollars on the mixing panel and additional filtration system. Bottled oxygen needs to be obtained
from your local gas Gas Distributor.
- Lowest initial startup cost
- Able to mix any mixed gas percentage
- Very tedious process - Substantial amount of labor, generally
20-30 min, to fill each SCUBA tank.
- SCUBA tanks and fill system need to be Oxygen Clean Certified - more
expensive VIP process.
- Potentially dangerous if oil has been inadvertently admitted to SCUBA
tank (diesel effect resulting in explosion)
- Unable to use all Oxygen in O2 Tank unless you have a Booster Pump.
Usually send O2 tank back to Gas Distributor with ~400 psi.
- Accuracy of Nitrox mix is dependant on the proficiency of the person
operating the fill station.
- Need to have readily available supply of Oxygen
Greg McLaughlin from Jack's Diving Locker in Kailua-Kona, Hawaii, wrote a
great partial pressure blending calculator for the iphone that will also work on
your web browser. It works best on Firefox or Safari.
More information about the calculator is available at:
Nitrogen Separating Membrane:
This technology was initially developed by the welding industry to generate
Nitrogen. It uses a low pressure air source (or a high pressure air source
regulated to low pressure) to force heated air through a special membrane
system. There are two outlets from the membrane: one for the nitrogen
vent, and one for the permeate (enriched Oxygen mixture) that goes into your high pressure air compressor.
There are a couple different variations on this design. The oxygen content
is controlled by either adjusting the input
pressure to the membrane or adjusting the nitrogen vent. The membrane is
unstable initially until it reaches operating temperature (~30 min).
Adjustments to the membrane input pressure or nitrogen vent typically take about
a minute before their affects stabilize at the oxygen sensor at the inlet to the HP air compressor.
The outlet of HP air compressor is either sent directly into SCUBA tanks or a Nitrox
Bank. More information about nitrogen separating membranes is available at
- Requires no bottled oxygen, independence from oxygen distributors.
- Can safely make Nitrox up to 40%
- Scuba tanks and fill system do not need to be oxygen clean.
- Expensive initial procurement cost - typically on the order of
$15-20K for a system capable of delivering 36% Nitrox at 15CFM
- System is slow to start up and can be frustrating to operate - difficult
to dial in desired oxygen mixture. The heated air fed to the membrane
causes the chemical reaction in the oxygen sensor to speed up, significantly
throwing off oxygen analyzer calibration.
- Additional costs (electricity/maintenance) associated with running low
pressure air compressor to supply air to membrane.
- If HP air banks are used to provide input air pressure to membrane - there is an
enormous amount of wasted HP air and associated HP compressor electricity
- If filters are not frequently changed, membrane can get clogged with
dirt particles, requiring its replacement - expensive!
- Membrane is fragile and can be damaged due to carelessness, if over
pressurized or not properly heated (making the tubes brittle), you can
easily burst the small tubes inside, requiring the membrane to be replaced -
- Replacement membranes are expensive! If system the is equipped
with a LP compressor, a replacement membrane represents about half the cost
of the system. If the system uses a HP to LP regulator, the
replacement membrane represents about two third's the cost of the system.
A replacement 6 foot membrane (used with 15CFM compressors) costs $8K.
- System should be constantly monitored during operation.
- Usually the highest cost per Nitrox SCUBA Tank.
Continuous Gas Blending with Nitrox Stik:
The Nitrox Stik continuous gas blender uses
O2 tanks and a patented blending “Stik” to homogeneously mix air and
pure oxygen at the inlet of a high-pressure air compressor. Placing the system
on service involves isolating the system's air storage bank, bleeding all the
air out of the lines on the discharge side of the compressor (this reduces the
time it takes to purge the air and replace it with Nitrox), and then while the
compressor is running, placing the oxygen tank on service and throttling the
oxygen supply to achieve the desired oxygen concentration. Continue bleeding the
discharge of the air compressor until the system is purged and the oxygen
analyzer monitoring the outlet of the compressor indicates the desired oxygen
air compressor, associated filters and air lines have now all been purged
and he outlet of HP air compressor is either sent directly into SCUBA tanks or a Nitrox
Bank. It typically takes between 5-10
minutes to place the system on service and start filling Nitrox SCUBA Tanks.
- Moderate initial procurement cost - $2300 for the Nitrox Stik and an
additional $2700-$3200 (depending on size of HP compressor) for the Nitrox
- Can Safely make Nitrox up to 40%.
- Scuba tanks and fill system do not need to be oxygen clean.
- Nitrox Controller allows operator to attend to other matters while
filling Nitrox Tanks, reduces labor costs, increases accuracy of Nitrox Mix,
and has additional safety features.
- Usually lowest cost per Nitrox SCUBA Tank by far when considering oxygen, labor and
- System should be constantly monitored during operation (unless Nitrox
Controller is installed).
- Need to have readily available supply of Oxygen.
When taking everything into account, the Nitrox Stik with the Nitrox Controller
usually makes the