Slow & steady little compressor- curious and/or seeking

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seascaper

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Location
Montego Bay, Jamaica
# of dives
I just don't log dives
Wisdom pool,
I'm wondering if there exists a little electric compressor that could fill a whip of 1/2dozen+ tanks on an overnight trickle.
quiet as possible, 120 or 220V or 3phase, and 50Hz in a perfect world.
I'd set an alarm to check it from time to time, and/or a baby-monitor.
Andrew
 
It would need to have auto drains and a cutoff switch to run it that way which would add cost.

I have a Bauer 5 cfm Capitano setup with a 3hp 220V single phase motor. Runs off a 30 amp circuit, but has manual drains. If I had to do it again I would look for a quiet K14 with auto drains and then fill banks. Listening to that thing bang is one of several reasons I switched to a rebreathers (vs filling several sets of doubles with trimix).
 
Wisdom pool,
I'm wondering if there exists a little electric compressor that could fill a whip of 1/2dozen+ tanks on an overnight trickle.
quiet as possible, 120 or 220V or 3phase, and 50Hz in a perfect world.
I'd set an alarm to check it from time to time, and/or a baby-monitor.
Andrew
I own one of those. Auto drains with the interval based on humidity and temperature. Auto shutoff at 3 separate pressures chosen by a switch. Low oil pressure shutoff. I could build you another one for about $7k. But I wouldn't make much money doing it.
 
My first impression is that for your application of simply filing scuba cylinders with breathing air a “trickle rate” compressor is not the direction you should be looking in. To my mind pump the biggest bang for your buck that the power available to you will allow and if you have spare capacity fill HP bank cylinders as a store/back up for later.

But If the question is does there exists a little electric compressor for your requested requirement the answer is yes and it’s pretty simple to build and self service. However IMHO its not the best use of the compressor components for your specific application.
Therefore I’m purely answering for the sake of the question, so first some technical implications.
1. Define the plus + in your 1/2 a dozen, is that six cylinders or if more? and if so how many more.
2. Define running overnight, is that 8 hours or 12 hours or do you have a specific time slot.

The answer to these two questions gives you your required flow over your defined filling period.
For example assuming a rounded up 80 cfm per cylinder. Six cylinders over an 8 hour filling period is a 1 cfm compressor, as is 10 cylinders over 12 hours.
So to kick off your looking at around the 1 SCFM mark (continuous duty rated *** ) with auto stop and automatic separator drains and running overnight solar power is sadly out of the question.

*** Continuous duty rated is an absolute must if you expect to compress the last 1/3rd of the charging time at high pressure over a 3 hour period and this is much more than the typical 20 minutes allowed with a typical scuba compressor design. Further most oil lubricated scuba compressors are not designed for this type of low RPM speed applications.

In a nut shell too hot running for too long a period of time with the rods and piston sets under continuous high load and heat is not fair on a typical oil lubricated scuba compressor design.

Also this limits the available compressor blocks you can us for this application we discussed a similar requirement a couple of posts back. A 1.0 BHP 0.75 Kw motor. Running a specific compressor piston set at 865RPM to give you 1.1 SCFM At 3300psi oil free and oil less over a continuous duty cycle.

For brevity this 865RPM reduction is from the optimum standard 1500RPM and against the maximum allowable 2200RPM for the small 3 stage oil-free, oil-less piston set.
 
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5 CFM Bauer and a couple three cylinders for air storage. Not many or any that I have ever heard of have the last stage floating piston like the Bauers. Love that Rod knocking sound when one of my 3 Bauers starts up. Plus 1000 PSI oil pressure to the last stage.
 
5 CFM Bauer and a couple three cylinders for air storage. Not many or any that I have ever heard of have the last stage floating piston like the Bauers. Love that Rod knocking sound when one of my 3 Bauers starts up. Plus 1000 PSI oil pressure to the last stage.

Good luck running that idea at 1 cfm............. for long. LOL
 
Thanks Ian,
I've got ~20bottles in the current collection, old and brand-spankin' new.

We use 6~12 bottles/day in set-up & monitoring days and <6/week through grow-out phases. Perfect-world there'd be something at ~1cfm on some manner of quiet & high-efficiency motor (island= electricity is costly). It sounds like that last 1000PSI is excessive work/duration, as I'd thought it might be.

Larger machine is more noise, thus timing issues with work, sea, sleep, neighbours etc. and/or tank-changes at X-minute intervals. I'd prefer to go to bed and wake up to a rack of ready-to-go bottles but fully appreciate the risks with "set & forget".

(Amongst) my problem(s) is the down-time of compressors at dive-shops & Marine Park office (mechanical & professional), plus time, travel & traffic in drop-collect. Autonomy is becoming my general ethos with efficiency getting to be getting to more important than actual cost, though I'm still a wee start-up so up-front cost remains extremely relevant.

Steel banks only go to 2500PSI, no? Thus still need to let machine run at elevated PSI, then start machine to top-up before work-day or spring for the Haskel? I'm trying to not make yet another investment (in gear & importation, space, time, risks etc) if there's an option, though I appreciate that there's not much for options unless I take BRT's kind offer (thanks, but it'd strain the budget for now).

Thanks again,

Andrew
 
If this were me, small island, expensive on power and remote with 6-12 bottles a day to fill (with my own compressor.)
I would really consider the following tweaks:

1. Reduce the full pressure of the cylinders from say 3000 psi to say around 2200 to 2500psi. The advantages are as follows:
This will have little bearing on your TTUP although some consideration on reserve air, dive profile etc may be required.
2. If possible compensate by using bigger volume cylinders. For example a Euro 10L cylinder at 232 bar gives 2320L by volume compared with a 12L cylinder at 200 bar gives more at 2400L. While a Euro 15L cylinder at 154 bar (2240psi) gives you the same 2325 L as the 10L

3. Even if your using American Specs 3000psi cylinders commonly called the 80 a (207 bar x 11L ) 2277L consider the LP112 or 104's at 2400+ psi The advantage is a faster filling time per cylinder (not charging rate)

The argument on a small trickle charge doesn't work in that half the power for twice as long uses more power, while lowering the final pressure uses less power and increases the mean time between servicing due to the reduction in rod load. If you reduce the rod load by a 1/3rd you double the compressor ring life.

Of course this is of no interest if your getting your cylinders filled elsewhere save maybe a reason why the compressors are always broke
But that would be my first observation of an avoidable problem with local dive shops.
 

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