Question Best setup for filling at home

[rob.mwpropane]

What's a good price for a Rix SA-6? I am looking at a used electric motor version, and curious about what would be a fair price assuming good condition.

Oh man, that's a loaded question. As least expensive as you can get it for? I paid $2400 for mine (diesel), a buddy paid $600 for his (gas) but it was missing the fan cover.

If it's a stock Rix it will need additional filtration to dry the air. I got mine from American Airworks for $400+ (I did not know I needed that at the time of purchase of the Rix so that was a salty purchase). Fittings, hoses, gauges and what not ran me another ~ $1000. If I had that to do over again I would have bought as much used parts as I could. And this was all before covid, so these prices are different now.

If you find one and it looks in good shape send me some pictures, I'd be happy to take a look. You're mainly looking for a cleaner unit (somewhat indicative of being taken care of), dual belts, stainless steel heads, and a fan with 8 blades but I use an additional fan so one with less wouldn't be a deal breaker for me. It seems to me newer fans are black and older fans are white?

The higher the serial number the newer the unit. For reference mine is 12509 and is one of the newer ones that I've seen.

Just trying to give you an idea what you're in for or what yo look for.

 

[iain/hsm]

Topic 4: Do you have any guidance in silencing the compressor, without making it to overheat? Somebody created a custom water cooling? Or additional fans in a sound deadened box?

To silence a divers breathing air compressor
1. Remove the fan

To lower the noise output from the compressor
2. Remove some of the fan blades say from six blades to say four blades while always keeping fan balance
3. Lower the pitch angle of each of the blades from say 30 degrees pitch to say 0 degrees as found in the likes of large desk or room ventilation fans

To lower the noise generated by the compressor
4. Lower the RPM say from the typical 2100 RPM to say half that say 750 RPM This does require some consideration as to make and model.

This would give you the further option of say using a bigger 150 LPM compressor with normally a 3.7 to 4Kw of required power but this size of block would generate around 90 to 120LPM with a half size half speed (RPM) say 3BHP 2.2 Kw motor. Both motor options are available in both single or 3 phase and as your running 240 volt 50 Hz domestic power in Europe you could even run a 3.7Kw single phase capacitor start capacitor run motor and develop 160LPM flow to around a maximum discharge pressure of say 350 bar G while still running 240 volt single phase supply.

Now 3.7Kw motor would be like installing a domestic house oven 16 amps
If you require a domestic plug 13 Amp ring main then the largest motor you could use would be the 2.2Kw 3HP

Lowering the RPM does not affect the cooling so at half the speed you create half the flow and develop half the heat generated. But again it all depends on the details ie make and model etc etc.

Dissipating heat from the cooling coils or long tube is also possible by using a coil within a coil or tube within a tube method imagine say a 3/8" OD high pressure gas tube poked inside a 1/2" to 3/4" water hose and the cold water flows over and around the metal gas tube and neither gas or cooling water ever meet (hopefully)

Stuffing the compressor inside a big metal box and sticking foam rubber to the internal faces is for the idiots the clowns and the ignorant foolish. Failing that I guess painting it black and calling it Technical Dive System or some such usually works wonders with the dive gurus, scuba ambassadors and sundry fanboys. Iain

 

[iain/hsm]

Topic 3: how do you actually create a buffer system. What connectors from compressor to buffer are needed, and from buffer to tank? I see those inox metal pipes at the local dive shop, but can't find where to buy these to make a custom system.

First I should define a Buffer System as I think you may have meant a Bank System.

A Buffer System consists of two pumps the first is a standard scuba air compressor that fills a small bank of say 3 cylinders each 50 litre water capacity to say 100 Bar G

Then a second pump known as a booster pump takes that 100 bar G pressure from the bank and boosts it up to the required 200/300 or 350 bars pressure depending on the gas pressure generated to either scuba cylinders or an additional storage bank usually comprising of the same 50 litre site cylinders but rated for 350 bar G service pressure and can be a bank of say 6 to 16 cylinders depending on the size and demand of the filling operation.

By using this method you can create the equivalent of a 16 CFM 450 LPM "compressor" system using only two 240 volt single phase domestic 13 amp plugs. The first plug fits to the compressor and is your 3.7 Kw motor and the second plug fits to the motor on the booster and is the 1.1Kw (1.5BHP) motor

Rarely done in the scuba world but is an efficient and effective way of generating high pressure storage while saving wear and tare on the air compressor as the air compressor runs only up to 100 bar to achieve the same setting as a typical back pressure regulator thereby not reducing the performance of the molecular sieve dehydrating filter towers. While at the same time the little 1.1Kw booster runs at a very conservative 2:1 ratio of say around 100 bar inlet 200 bar outlet with your 450 LPM flow and kicking the ass off anything else. Although some skill in mechanical balance is required a Buffer System as I know it is used mostly with military or pure gas generator companies with gases such as oxygen. Iain.

 

[Umuntu]

, with apologies …

@iain/hsm

A small dive club on a remote island with good local food availability, but anything industrial - spares , replacement parts etc. - difficult, is looking for a compressor with an emphasis on reliability. 8 to 12 tanks a day. Maybe a little more on weekends. Not much else going on.

Electricity available 240v, but when it goes reliant on own generator.

Subject to above, if possible, ability to do nitrox (membrane, not mix; no O2 availability) a definite advantage.

What would you recommend ?

Thanks in advance for your experience and expertise.

 

[iain/hsm]

I'm facing the fact that I have to fill 6 to 8 tanks of 12L, 2 to 3 times per week.

Before answering your Topics 1 and 2.
I guess you realise I'm working your questions back to front (again) as its easier.

So to your 300 Lb gorilla in the corner question.

You intend filling 6 to 8 cylinders (Tanks are what the army drive) each 12 litre water capacity
2 to 3 times a week is the good news

The bad news however is how the heck you expect to do this with 100LPM without running a night shift and at that if your wife will allow you. My guess is I will give it 10 minutes before your a dead man walking.
Can I suggest you buy her ear defenders for Christmas. Iain

 

[iain/hsm]

What would you recommend ?

For a diving operation on a small remote island.

Sell a half decent average size family car and buy the following

1. A small two man transportable recompression chamber 50MSW 165FSW capable
2. A small Pressure Swing Adsorber oxygen generator 95-98%
3. A good first aid kit and have someone complete a Diver Medics and Chamber Course

That way you can carry oxygen on board for any emergency management
and have a spare oxygen cylinder for the chamber BIBS masks in the chamber (Built in Breathing System)

The kick off position to me would be the risk assessment and management for when it all goes pear shape. (Tits up is the British vernacular but I'm not sure this is acceptable term today)

Failing that the next consideration on a specific suitable compressor would be A.R.M.
Availability, Reliability and Maintainability

You would need spare parts readily available, for ease of service with the minimum of tools
No special tools to take say the valves out for example and standard tools to service. Wrench Allen Keys sockets etc
A reliable proven rugged design preferably built for a military application with a NSN or NATO stock number (as someone else did all the required testing )
A rugged repackable filter chemical system with a visual indicator to monitor filter performance in real time.

A back up plan if the filter fails and you really need to go diving so an oil free compressor and aluminium cylinders that can tolerate high humidity condensing air fills with a wrench to open the cylinder valves (when empty) and let any condensed water vapour inside evaporate out in the sun.

Add an extra line heading in your SOP to check for crawling things inside the cylinders before replacing the cylinder valve. The rest is just detail. Iain

 

[grantmac]

What's a good price for a Rix SA-6? I am looking at a used electric motor version, and curious about what would be a fair price assuming good condition.

Pretty sure we are both looking at the same unit. Seems rather expensive to me.

 

[Umuntu]

A reliable proven rugged design preferably built for a military application with a NSN or NATO stock number (as someone else did all the required testing )
A rugged repackable filter chemical system with a visual indicator to monitor filter performance in real time.

Thank you !

I appreciate your reply.

And what would this Unicorn compressor unit be called ? A serious question.

SOP is relatively shallow diving. Rec, no Tec. Longer safety stops (aka preventative in water decompression ). No tourists. I appreciate the advice about mobile chambers. Those seem to be becoming more available … I even get Ads for them in my browsing.

 

[iain/hsm]

And what would this Unicorn compressor unit be called ? A serious question.

That's easy.

How about we all call it the "UNICORNUS 6S" (after the great one horned Rhino) after all Bauer have the "UNICUS 4S" Alternatively never let engineering handle your advertising sales and marketing ideas. LOL

 

[iain/hsm]

SOP is relatively shallow diving. Rec, no Tec. Longer safety stops (aka preventative in water decompression ). No tourists. I appreciate the advice about mobile chambers. Those seem to be becoming more available … I even get Ads for them in my browsing.

All diving starts with planning and risk assessment. Then logistics practicalities and finance limitations kick in while risk tolerance increases to meet the increasing financial limitations.

Incidentally the chambers I suggested are full depth 50MSW 165FSW and capable of performing a full USN treatment table (in a remote area) and not those inflatable "Soft treatment" shallow inflatable bags for the pseudo science medical fraternity made for profit we both have now seen advertising on this forum.

As for the compressor I wouldn't get hung up on the make and model just yet until all the parameters of your application are known. Similar to the OP's requirement until you know these parameters you can't make a blanket recommendation.

For example the question "How many cylinders do you want to fill and of what size and how often per day impacts the size of compressor needed coupled with the available power required. Three dives a day with 12 of you using single 12's or the occasional bail out nitrox fill for you and the wife would result in two different products.

By contrast servicing or more specific self servicing of the compressor is to you of greater importance diving off a remote Island while the OP filling at home this would be of lesser importance.

Another example to me would be for both of you power availability would be my first consideration but with two different conclusions.
First for yourself on the remote Island maybe consider a second back up or even a smaller compressor petrol or diesel driven in the event of electric power cuts. While to the OP filling at home this would not be that good a suggestion.

To me It all kicks off with application against cost both are interesting contrasts while the make and model at this stage of the conversation/suggestion are not as important.

As our collective understanding and knowledge grows the choice of plant used becomes much simpler and clearer to all. Iain