Compressors

[bigjo]

Could anyone offer some advice please. My club is considering buying a nitrox compressor and I wondered if anyone out there could make some suggestions, some idea of price, maintainance costs etc.

[Phil Laughton]

Nitrox compressors are few and far between and you might find they are also quite expensive. The only one I have seen advertised is the Coltri unit sold by SMP. If you contact them they should give a price for a new unit.
If your club has a air compressor you could modify it to give O2 clean air, which would be a cheaper option for the club.

Phil

[IainC]

I have looked into this.

What is your budget? If less than oh, about £10,000 forget it!

If you have a compressor already, the cheapest way to get nitrox is to add a second filter to make sure it meats the standard for oil-free/O2 clean air and then get some blending equipment and some Js of O2 for mixing (make sure the blender knows what they are doing, a course will cost about £100 quid). cost of exta filter and blending whip with needle gauge, plus sundries, will be well under £1000.
Ongoing costs are the replacement filters, rental of O2 cyldiners, etc.

If you don't have a compressor, the cheapest way is still to get a normal compressor, then do as above..

If you want mixes up to 36%-40% you can get a membrane system.

A membrane system goes before your normal compressor - it has a low pressure compressor (up to 10bar or so) and a membrane to filter out some of the nitrogen. You dial in the %O2 you want (this adjusts the low pressure compressor, basically, changing the efficiency of the membrane and hence how much %O2 you get) Then your normal compressor pumps the output from the membrane up to 230+ bar into your tank.

The membrane system will cost at least £5000 and needs to be sized for your compressor. If you don't have a compressor already, you need to buy one of them too :)

There are one or two combined systems on the market, search for 'nuvair'. The explorer two is an 'all in one' system, it is small (3.5cfm, which is about the slowest compressor you'll get) and I was quoted £7000 + VAT for it. with single phase electric or petrol engine

A bigger one (MCH 14, 8.5cfm, 3 phase electric) about £15000 + VAT.

This from SMP - UK dealer for 'nuvair' who are a US compressor company.

Hope this helps,



Iain C.


--edit for clarity & spelling

[Beanie]

For price guide look at: http://divertec.net/catalog/index.php?osCsid=dec7de2aa52d59b85e6f539218db4736

[iain/hsm]

In Leicester the nearest nitrox compressor system would be at ADM Diving Unit C, Chantry House, Grange Business Park, Enderby Road, Whetstone, Leicestershire, LE8 6EP Tel: 0116 278 7711 Fax: 0116 278 5578
Email: mail@admdiving.co.uk
ADM have two oil free oil-less units, a 350 bar 160l/min 4Kw 5.5 HP oil-less high pressure compressor for both air and nitrox and a 2hp 1.1Kw single phase 230Volt 350 bar electric booster pump for the oxygen/helium.

May be worth giving them a visit to see what the sort of engineering the set up looks like. Both of the compressors, the panels, storage bank and filter system were built local to you in Loughborough, so not far there either.

The charging panel separates air from nitrox as does each of the charging lines to avoid cross contanination, The compressor output is filtered to 2Mu as are all the external oxygen/helium source gas supply input lines at the bottles. Gas purity is analysed in line at the point of dispencing both for air quality, continuous inline water vapour and for 02/He.

The main storage bank consists of 18 off 50 litre 350 barg cylinders of various mixed gas, banked for all major mixes including oxygen at 250 barg and Helium at 350 bar, each cylinder is filtered to 2Mu at the connection bullnose
There is a second bank and gas storage cage next door hooked up to 8 oxygen and 4 helium cylinders from three manifold panels routed to the booster pump also filtered at the bottle to 2Mu.

The whole plant is completly oil-free and oil-less to ensure gas purity, with a full tracable bar code system from the gas supply source throughout storage from each storage bottle, out to the customers delivery cylinders.

If you need any more pictures of the rest of the plant (or better quality) let me know. Iain

[IainC]

iain/hsm - I think he wanted it for his club? They'd have ot be pretty well off to asfford THAT setup!

Iain C.

[iain/hsm]

Granted, but as the club is already in Leicestershire and with the kit already on the doorstep so to speak, I thought it would be worth suggesting a chat with them before going much further. At worst you could get a fill, to try at least.

As for any other club it’s just a matter of budget and scale, the individual breakdown of parts used and their individual costs. Half the storage bank size and you half the cost. It’s just a matter of parts used.

I don’t think it has to be as expensive as suggested in previous posts or indeed as simple, we just need to have a fuller picture of the options and risks. Granted a local tame engineering team that can machine supply and install at an engineering cost helps, although the option of an off the shelf unit from a scuba supplier still remains.

Cost is only part of the consideration but if you take the compressor alone it was a stainless, 350 bar oil-free, oil-less 160L/min, high pressure nitrox unit, cost was £4,200, conversely the 350 bar Bull nose cylinder connections complete with the 2Mu filters were £7.50. Iain/HSM

[IainC]

Cost is only part of the consideration but if you take the compressor alone it was a stainless, 350 bar oil-free, oil-less 160L/min, high pressure nitrox unit, cost was £4,200, conversely the 350 bar Bull nose cylinder connections complete with the 2Mu filters were £7.50. Iain/HSM


That surpises me.

I may ask you for some advice then :)

Looking for oil free compressors I have only found low pressure industrial things on the web.

If an oil free breathing air compressor is not that much more expensive than a oily one, where do I find one?

What are they lubricated with (or do they run dry?)

Are they any easier/cheaper (or more complicated/expensive) to run and maintain?

Iain.

[iain/hsm]

The nearest oil free compressor to you in York would be Vandagraph Limited 15 Station Road Crosshills Keighley West Yorkshire BD20 7DT www.vandagraph.co.uk They manufacture divers oxygen and helium gas analysers and sensors and use their oil free compressor for testing medical oxygen sensors. John Lamb is the MD and would give you a reference about the compressor he has had it 10 years but doesn’t fill divers cylinders apart from his own semi closed unit.

The lubrication is basically a Tribology development for the military, as they wanted a compressor that would not pollute HP cylinders without the additional chemical filtration. Tribology is basically wear tear friction and lubrication of materials, apart from that the compressor is like any other, just various diameter staged pistons designs on a swash plate conrod of a given stroke and a fixed RPM. The stroke and RPM give you the piston speed, the diameters give you the compression ratio.

Where it differs is using for example a bronze piston in a precipitation hardened stainless liner, but using solid PTFE rings, these seal the gas and also act as the “solid” lubricant as the piston travels up along the bore during compression. The compressed gas is pushed into a stainless steel head via conventional stainless steel common inlet and outlet reed valves.

Unlike oil lubricated units the HP gas cools quicker and as the only by product is pure distilled water this is condensed out during compression by stainless inter stage cooling coils and is simply collected and drained from two small water separator towers. Being pure water you can drink it if you want.

The alternative of the emulsified oil and water gunk from conventional compressors that has to disposed of in a responsible manner, not down the drains, coupled with the risk of oil with oxygen fire is not a good solution.

[iain/hsm]

Are they any easier/cheaper (or more complicated/expensive) to run and maintain?
Iain.

Sorry Iain I should have used quotes in my earlier reply.

No self servicing is both easy and cheap as by and large the major cost is in labour and travelling, not in parts. As with a lot of military type products servicing is done in the field by the users, using basic hand tools as no special tools are required to remove say the valve heads unlike some sports compressor designs.
Parts are basic PTFE compression rings and Viton 0-rings, for each stage piston and viton O-rings to seal the stainless valves. Takes about 20 minutes including making tea. Each head has three 0-rings, to seal the two inlet/outlet reed valves and the head to piston liner. These are standard industrial sizes and 70 shore compounds, both are disclosed in a manual.

The only extra is that the military like aircraft quality, cure dates and compound batch numbers to ensure there 0-rings are not old things that have been on some hydraulic shop sales floor for years, Hydraulic shop O-rings being famous for using out of date and out of tolerance rings for static hydraulic oil sealing. A date of manufacture, compound and cure date helps resolve this.