Do I want a compressor?

[OkByMe]

This is a Cornelius and is like mine. We were both born around the same time (early 50s). It takes about 40-45 minutes to fill a steel 72 to 2475. The maximum pressure is 3000. I got mine for $300. It is adequate for my needs. I rarely fill more than two tanks in one day. On the front, right, is the pressure relief valve which can be set for various pressures. Since it does not have auto-shutoff I taped a plastic bag around the valve so it fills up with air when my tank is full. I can see it from a long way off.




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You can add an adjustable pressure cutoff switch... 0-6000psi. - like the grey box on this setup, EBAY - have to look for it. don't pay more than 60 bucks, it is surplus. Cut your power cable and put the ends across the normally closed switch. Remove the whip and add a "tee" for a 316SS line to the switch. Adjust the pressure cutoff on the switch to the tank pressure you want.

not really wanting to get into your procedures.... but it has been my experience to have to drain the condensate trap 2 or 3 times per fill. Since I added auto drains and the cutoff, I can just walk away.

 

[OkByMe]

I went back to my post to get a picture and discovered an error in my statement: I said $6000, not right. That cost includes all my SCUBA cylinders, bank cylinders, compressor, Oxygen generators and test equipment. This is the $3000.00 compressor

 

[Schwob]

I went back to my post to get a picture and discovered an error in my statement: I said $6000, not right. That cost includes all my SCUBA cylinders, bank cylinders, compressor, Oxygen generators and test equipment. This is the $3000.00 compressor

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That picture is good to see. Thank you. So much better than words to help me to understand that I have to work a bunch on my understanding...

 

[JamesBon92007]

View attachment 425288


You can add an adjustable pressure cutoff switch... 0-6000psi. - like the grey box on this setup, EBAY - have to look for it. don't pay more than 60 bucks, it is surplus. Cut your power cable and put the ends across the normally closed switch. Remove the whip and add a "tee" for a 316SS line to the switch. Adjust the pressure cutoff on the switch to the tank pressure you want.

not really wanting to get into your procedures.... but it has been my experience to have to drain the condensate trap 2 or 3 times per fill. Since I added auto drains and the cutoff, I can just walk away.

I've repaired/replaced pressure switches on wells and LP compressors so it's been on my mind but my plastic bag works so well!

I've pondered shutting it all down and emptying the water trap during the fills but didn't really see a need for it. How do you determine when it needs to be emptied?

 

[OkByMe]

I've repaired/replaced pressure switches on wells and LP compressors so it's been on my mind but my plastic bag works so well!

I've pondered shutting it all down and emptying the water trap during the fills but didn't really see a need for it. How do you determine when it needs to be emptied?

It depends on the trap. The trap between the first and second stage will have the most but all traps will have some moisture. There is usually not a trap between the second and third stage since you will be working at or above 500psi and they get pricey. The trick is that you do not want water to hit the sieve in the filter. The gas enters the bottom of the filter stack and in a fully pressure saturated filter the water falls out. Also... you should not have to shut the compressor down to bleed the trap or the filter. There should not be any significant pressure drop to unload the compressor when you open the bleed valve. - just crack it.

 

[BRT]

This is a Cornelius and is like mine. We were both born around the same time (early 50s). It takes about 40-45 minutes to fill a steel 72 to 2475. The maximum pressure is 3000. I got mine for $300. It is adequate for my needs. I rarely fill more than two tanks in one day. On the front, right, is the pressure relief valve which can be set for various pressures. Since it does not have auto-shutoff I taped a plastic bag around the valve so it fills up with air when my tank is full. I can see it from a long way off.




View attachment 425193

I have one of Jim Sheldon's Kidde compressors, heavily modified with auto drain and auto shut off. About 1.8 cfm and I hook it to 3 tanks and let it run. It is in my shop and I look at the O2 and CO levels as I walk by occasionally. The beauty is that it takes up very little space.

 

[lionfish-eater]

Here is another small setup capable of handling twin tanks. LOL

 

[Brandon]

Right sized = capable of filling your typical loadout of tanks in a reasonable amount of time. That will vary by diver. For me, I can count on needing to do about 300 CF of nitrox per week.

300 CF / 3 CFM = 100 minutes.

Making the two trips to and from the dive shop takes at least that (20 mins each way, 10 minutes to pick/up, pay and analyze).

At local prices, nitrox is $.20 per CF (and actually a little more due to regular short fills). With that taken into account and fuel costs for the travel added in, it goes up to $.28 per CF.

Nitrox currently costs me $.12 per CF, all in. Electricity, oxygen, filters, oil, sensors, OCA test, maintenance, etc. I don't account for my time, because it's equal to the amount I'd spend travelling to / from the dive shop.

When I was still paying off the compressor acquisition costs, total was $.32 per CF.

It took two years to break even and was totally worth the extra $.04 per CF.

Trimix fills are a joke- same as TrimixToo, cost of one commercial LDS fill = roughly six fills at home, with a lot more flexibility. I move gas around all the time. 1400 PSI of trimix in a set of doubles isn't particularly useful for a dive, but it is a full AL80 stage fill. Deco fills are ridiculously inexpensive compared to local costs.

Gas quality is superb. I can taste/smell the gas from both of our local dive shops. Mine is clean with no taste/odors and I have the regular test results to back that up as well. No one cares as much about filling my tanks properly as I do.

I have a spreadsheet I can send you that will help to calculate costs if you pm me an e-mail address. Depending on how often you dive and what your local fill situation is, it is possible to save money on fills while gaining convenience and a greater sense of security. You just need to do the math.

-B

 

[Co. BAtguano]

I put in a used Mako 5 cfm unit with the constant CO monitor about 3 years ago, and am glad I did. I teach independently, and average about 250-300 fills per summer. With 3 x 3500 psi bank bottles (I regularly fill them to a 10% overfill) and 2 fill whips I can usually get about 10 fills out of it with the compressor running before I have to wait on it to fill more dive bottles.. Since I have about 28 dive tanks it's rare that I have to wait on the compressor to get me to the point where I need to wait on it to have enough tanks to provide enough for the next day's class of dives. Generally, I try not to run the compressor more than 2 hours at a time, just to keep the heat down. It seems the hotter the unit gets, the more stress it puts on the filter, and more prone it is to generate CO. I thought when I got the unit that having manual drains was going to be a real PITA, but it turns out it's really no big deal. Come Sunday night, I might have 24 empties, but I have the whole week to re-fill those

I change my filter and oil about every 50 hours, which is overkill on the oil, but that too helps keep the CO generation down. Another thing is to try to keep your back pressure to 2000 psi or greater. You never really know if those check valves are working (most don't) so the back pressure from the banks will serve the same function to keep the filter under pressure.

Toward the end of the summer, I try to enter the fall and winter with as depleted of banks as I can, and as many depleted dive tanks as I can. That way I can run the compressor for about 30 minutes every couple of weeks in the fall, winter and spring, and capture the air I'm "paying for" anyway. It's either that or tear the whole thing down and pickle it for 7 months, and tear it down again in the spring to unpickle it. I find it easier to gust flip the switch and run it every couple of weeks. It also becomes something of a secondary heat source for the basement in the winter. I figure my filter, oil, and electricity costs at something right around $0.45-$0.50 per fill.