If money were no object....

[tlarcombe]

If money were no object... which compressor would you buy?

I want to buy a new compressor. Currently I have a Paramina Typhoon and a Coltri. They are 13 and 16cuft/min respectively.

I would like to be able to fill up to nitrox 40. I would like low maintenance and the volume over my diving season (which is short) is about 12 x 12l tanks per day, every day for three months. Needs to work in a pretty warm ambient environment (summer temps around 40degC)

Ceramic? Osmosis? Any suggestions that would point me in the right direction to start my research would be much appreciated. I am in Europe if this makes any difference.

Finally, of course money is something I must consider - but it is not the biggest challenge.

Thank you in advance for your suggestions.

 

[tbone1004]

what is wrong with the two you have?

I'd personally look at a used Bauer if I were shopping new for that volume each day, but realistically the key is a big cascade system with the compressors you already have

 

[iain/hsm]

If money were no object I would first hire a professional compressor engineer who you can trust for a day to evaluate your requrements and application before even considering a brand name.

Your location, will lead to a number of considerations
From power requirements and reliability of your mains power supply to service and maintenance.
Items covered are from staff training onsite in complete strip down re build and service
and maintenance to calling in a service engineer and paying for his time and travel.

Your application also needs to be considered fully with safety options if you are reselling the product.
Also 40% at 40C ambient air temeratures needs some additional details.

But if money were no object I would also look at industrial air and oxygen compressors
and if possible some of the European military NATO mixed gas compressors for up to 60%
Rather than limit yoursef to just high RPM hot recreational scuba compressor models and brands.

 

[tlarcombe]

Thank you for your comments - the reason for a third compressor is that I am planning on opening a third premises.

It is interesting that power requirements and reliability come high on the list - this has historically been a problem.

Anyway, I have taken all your suggestions on board and will consider how top progress.

Thank you again.

 

[iain/hsm]

Thank you for your comments - the reason for a third compressor is that I am planning on opening a third premises.

It is interesting that power requirements and reliability come high on the list - this has historically been a problem.

Anyway, I have taken all your suggestions on board and will consider how top progress.

Thank you again.

Just as an exercise and to give perspective on this:
12x 12L tanks per day every day for 3 months 90 days

Your daily requirement rounded out is about 1200 CFM per day (12 x 12 x 232 (pressure bar)
And over your 3 month period would require 108,000 cubic foot. (3,058,560 litres) over 90 days

Now to take the point of money no object I would look at this differently.
And suggest an offshore commercial diving mindset for say a planned offshore air diving project over three months or an air diving application offshore from an air diving DSV but in both scenarios without running additional man-hours and a night shift. The planning and investment costs would be different but the reliability would be greater but with the overall running service and maintenance cost less than your present set up.

First if one man has to fill the tanks go diving, or come back after diving and refill for the next day. In both cases you would need to reduce the time waiting around filling to a minimum. The only practical way to achieve this is to increase the charging rate of the compressor.

Personally I also like the idea of being able to fill both before the dives or after without working half the night. So giving a flexible choice of filling in the morning before the dives, but also have the capability to fill in the afternoon after the dives without working say more than a 8/10/12 hour day.

This target of time reduction spent in filling is a balancing act between cost of a bigger compressor against the cost of employing an additional pair of hands to work the extra hours needed filling.

Presently you have a 13 and a 16 cfm I would therefore take this as acceptable start and first suggest that to kick off you consider an offshore spec industrial air/gas compressor of around 20-30 cfm.

Power required 11.78 BHP (8.78 Kw)
Low RPM: 582 RPM
Piston Rod Loading Design maximum allowed 1590 kg
Actual rod load on 1st: 336kg
Actual 2nd: 419Kg
Actual 3rd: 439Kg
Actual 4th: 338Kg

The above calculations tell you its first running at about 25% of its design maximum load.
And a low rod loading would be an advantage together with the low 582 RPM
This compared to your present high RPM hot 1500 and 1800 RPM choice.

Also for your nitrox application both the gas temperatures and the gas velocity need to be factored and are much more reduced when compared to any high RPM sports diving air compressor.

Further as the pressure in the compressor interstage increases the gas velocity reduces allowing a much higher nitrox safety margin than your required 40% and if required up to say 80% nitrox would be allowed giving a greater safety margin. Compare this safety margin to the zero margin that you work to with your present compressor choice.

Incidentally for pure 100% oxygen you would only need to reduce the CR Compression ratio on the 1st stage from 4.23 to 4:1 to make it an oxygen compressor (and it is already an oil free designed piston set)

1st stage Hot: 13.27 m/sec (CR 4.23:1)
1st stage Cold 12.48 m/sec
2nd stage Hot: 11.59 m/sec (CR 4:1)
2nd stage Cold:10.36 m/sec
3rd stage Hot: 2.55 m/sec (CR 4:1)
4th Stage Hot: 0.97 m/sec (CR 3.05:1)

This would be a kick off to evaluate and compare using a standard offshore commercial diving compressor than your two existing high RPM sports diving units.
Filter life provided would be designed for one filter change after your three month running if your planning a long 9 month lay up each year. Air purity would be BS EN 12021:2014 and for Nitrox the higher standard of BS EN 8478 :2011 would apply.

Servicing you would do yourself as offshore units include a full maintenance and service course for the dive crew and spare parts are both cheap easy to obtain and afford a long service life with a 80,000 hour crankcase bearing design life.

The cost varies on the parts you require and the fabrication material costs dependent on such factors as made in Super Duplex or 316 stainless steel. You do however have a full choice in the design, the automation and material choices to suit both your application and budget.

Consider also with an industrial offshore compressor you may not need the additional costs of a NACE certified NORSOK M501 Paint coat, or the x-ray and dye pen testing and certification for each of the material bar stock used in the machining or a hydro test for each of the pressure component including all tubing assemblies or an independent verification and certification from 3rd party's used for offshore installations such as Lloyds of London or DNV or ABS
with the additional incumbent electrical certification including EEx d/e and explosion proof.

Filling time for your 12 x 12L tanks assuming to 232 bar would be a total of 40 minutes a day.
Or 33 minutes for all 12 x 12L if at 200 bar pressure.
The maximum pressure for the design if using for example a storage bank would be 350 barg (5000psi)

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[tlarcombe]

That is an amazing and insightful reply. It opens up a number of possibilities that I had not considered. Iain/hsm - thank you very much for your time and effort on this.