Question Idle question from a possibly addled mind

[JohnN]

Is a RIX SA-3 suitable for use as an O2 booster. I have no plans to get into rebreathers, just curious

 

[rjack321]

Is a RIX SA-3 suitable for use as an O2 booster. I have no plans to get into rebreathers, just curious

No! You feed a compressor ambient pressure and it makes 250-300bar output from that. That is minimum 10x more than any recommended O2 compression ratio and creates an obscene amount of heat (at least for O2).

In booster terms that is like taking 250psi supply and creating 3000psi output - which is not a good scenario.

 

[iain/hsm]

Is a RIX SA-3 suitable for use as an O2 booster. I have no plans to get into rebreathers, just curious

No the Rix SA-3 is an air compressor. Read the label

But having said that if you pushed it up on the black board for an engineering review and purely on sound engineering practice and principle to explore the principle differences from a design philosophy (DP) perspective. Again it's a no go but from the DP position to make it work on oxygen the following would be required.

Take the 3 basic aspects of any scuba compressor
1. The Piston sets or diameters of each piston together with the number of pistons
2. The Piston stroke (Piston length of travel from Top dead centre TDC to bottom dead centre BDC
3. The RPM of the block

Then the only component of your SA-3 you could use to kick off with would be the 3rd stage piston diameter. But the Piston stoke you would have to double in length and the RPM you would have to slow right down from 2300 RPM to less than 200 RPM to get the same flow so that's the block ditched and your onto a new block design from the get go.

Although this would give you a near equivalent flow as your SA-3.

Now the problem is that the 1st stage now won't help you so you would have to ditch it off the drawing board as well and pushing the inlet pressure up to say 60 psi on the inlet stage to compensate. Or say down to 25psi to make the design really good as a scavenging pump.

Now with the 1st stage ditched the 2nd stage piston is now acting as the first stage and its now too small a diameter so a new inlet piston diameter is required.

Then add similar consideration to the valves heads pipework cooling interstage compression ratio, heat loading, cooling considerations etc.

Then in addition add the customers service life expectations, service components cost to customers, any special considerations or special tools required or be needed to service, Any practical oxygen cleaning procedure difficulties they may have etc. etc.

You get the picture

Then add any additional safety features low inlet cut out, high discharge pressure cut out, a high temperature RTD monitor and again another cut out. A micronic inlet particulate filter and the same on the discharge side. Include in your design criteria a 24/7 hours 100% duty cycle at 200 bar 3000 psi discharge pressure.

With all that junk your now double the weight of your original SA-3 and cost and you still need an ambient pressure air compressor for your air cylinders.

But at least you know it can be done just one part at a time.
At least it would have an oxygen label on it saying

This is an oxygen compressor not an ambient air compressor
Do not use at ambient inlet pressure

Just saying before someone asks if it could be used as an air compressor LOL

 

[JohnN]

No the Rix SA-3 is an air compressor. Read the label

. . . snip. . .

Speaking of the label:

I'm continuously blending EAN (32%) with no apparent problem, and the previous owner used it for tri-mix. Thank God I no longer dive with split fins. . .

But thanks for the other comments and engineering analysis.

 

[iain/hsm]

with no apparent problem

John I'm kind of thinking what factors led you to decide this stupid position with no apparent problem?

Rix Industries has for many years produced numerous high pressure pure oxygen compressors and has numerous professional experienced engineers some with diving skills that decided for a manifold of reason and consideration that your SA-3 is designed for compressing ambient air only and is not suitable for compressing oxygen, oxygen enriched air or oxygen enriched gases. Further they place a sticker in a prominent position on the compressor stating the obvious then it beggars the question why you would ask such a stupid question. Tired of living or just sheer ignorance?
Would you like another sticker to attach? LOL

 

[JohnN]

John I'm kind of thinking what factors led you to decide this stupid position with no apparent problem?

Rix Industries has for many years produced numerous high pressure pure oxygen compressors and has numerous professional experienced engineers some with diving skills that decided for a manifold of reason and consideration that your SA-3 is designed for compressing ambient air only and is not suitable for compressing oxygen, oxygen enriched air or oxygen enriched gases. Further they place a sticker in a prominent position on the compressor stating the obvious then it beggars the question why you would ask such a stupid question. Tired of living or just sheer ignorance?
Would you like another sticker to attach? LOL

Thanks Ian

I am using the SA-3 to fill tanks with EAN 32 (+- 2) using a blending stick. The PO also did tri-mix ( not my thing)

Id wager most people with SA-3/6 do EAN

I thought the label was put there out of an abundance of legal paranoia, not because of any engineering rationale

What would you predict the failure mode might be if I continue?

 

[iain/hsm]

What would you predict the failure mode might be if I continue?

There are two probable failure mode's for the SA-3 with nitrox on the FMA documentation and a number of other additional contributing factors.

The first is a kindling combustion effect due to the build up of common tree bark sap entering into the compressor past the standard scuba air version of the SA3 and SA-6 polyester mesh screen air intake filter. A mixture of pollen grain and sticky tree bark sap in the atmosphere together with all the dust dust pollen dead fly parts etc etc coat the reed valve and valve seats with a sticky junk like material and basically this will eventually build up and then burn off.

Now on atmospheric air it's a relatively safe and slow process but in the event you pump say atmospheric air for a couple of months to get a good build up of junk then jump to (on test gas ) 80% oxygen the burn off is quite rapid.

Now two question why 80% and how rapid. To kick off this was for the Royal Navy and others and the standard divers mixtures on test were 60/40 40/60 and 32.5% standard NATO mixes with the 80% being the upper test requirement. Similar to the hydro test pressure on a scuba cylinder of working pressure to test pressure being around 5/3rds the working pressure for safety.

Now as a small mark of understanding those who use Bauer and Coltri for nitrox may be interested to learn that neither Coltr or Bauer or anyone else I am aware of have undertaken FMA tests to see or even better to learn how this nitrox limit of 40% is affecting the breathing mixture with compounds that are not tested for in a standard air analysis program or the user being aware of or the risks involved breathing said compounds not withstanding the percentage over 40% that they have ever tested to.

So back to the air intake filter to start you need to reduce the micronic air intake filter pore size but without restricting the flow or intake velocity. Further a pleated paper element alternative will give a finer filtration than polyester but on a rolling deck with wave spray good luck using paper without creating paper mache clumps and clogging up the intake valve on the first stage.

Then the interstate filtration needs addressing your scuba SA-3 uses a dutch mesh stainless filter matrix again this needs to be changed to monel and a finer Mu element again with consideration to flow and deltaP

Then you need to address rjack321 points in detail

Then address the kindling effects in detail and make the required material change recommendations to reduce those aluminium components in any of the wetted wear parts. i.e. the separator spinner,
the separator cap plug, swap the taper threads to UNC parallel 0-ring seal BOSS type fittings,

 

[iain/hsm]

I thought the label was put there out of an abundance of legal paranoia, not because of any engineering rationale

The label on an oxygen compressor may say do not use at ambient inlet gas pressures if its otherwise designed or for ambient pressures such as in gas scavenging that uses a gas bag at ambient pressure and a specific compressor model designed for the purpose.

In addition the label on a nitrox compressor may have a reduced discharge pressure in the same way an oxygen compressor may have a further reduction in discharge pressure.

Look just read the label on any Coltri or Bauer Nitrox compressor it will clearly say Nitrox compressor on the data plate and state a maximum safe percentage and a maximum discharge pressure .........ROFL

It's all about the engineering detail. Read the label.

Its the failure of end users to read the flipping label that's the problem.

The legal aspect is I agree an element of requirement in todays world of idiots and stupid ignorance but what is the alternative.

20 years ago you were told in a car manual how to test the battery acid for performance. For today's idiot you have to tell them not to drink it.

Like this one eyed clown a couple of months back in our UK newspapers shoots himself in the head for a prank in the woods then regrets it.

I guess you now know the reason the British Government restrict the use of firearms to the general public.

 

[iain/hsm]

Id wager most people with SA-3/6 do EAN

The SA-6 air compressor is in a better position option wise than your SA-3 from an engineering perspective

But again taking another different FMA engineering consideration.
One of the polymers used on the SA-3 compression ring is very different to those used on the SA-6
and for an oxygen compressor the polymers are different again .

Now while the 3rd stage rings on your SA-3 air compressor could be substituted with same size rings from an oxygen compressor albeit with the oxygen compliant polymers just swapping rings doesn't make the compressor compliant or suitable due to other additional variants.

 

[tbone1004]

d

Is a RIX SA-3 suitable for use as an O2 booster. I have no plans to get into rebreathers, just curious

definitely not stock. It's possible but not without some serious work. It is a shame they discontinued the Microboost, but alas.

@Tracy has some Philips Ultrafills that will work for boosting O2.