Now might be a prudent time to take a quick look at some math, pertaining to operational expenses. These are just ballpark estimates. Specific examples will need to be calculated with actual data pertaining to specific equipment, using specific filtration media, running on power at a specific cost, and a specified maintenance schedule.
For the 3-4cfm machines, the filter system seems to usually be a water separator, followed by a second canister with a cartridge inside. Cartridges look to last about 20 fills of an AL80 tank on average, but that varies with temperature & humidity. Hot & humid kills them more quickly. Cartridge prices vary, but for these little machine, $50 seems to be a common price point. If you refill the cartridges yourself, the cost looks to be more like half of that, perhaps less. If we look at a $50 cartridge every 20 tanks, that comes out to $2.50 per fill.
Next lets look at power. If you run a 13 amp 220 single phase motor for 20 minutes, that’s 13 x 220 / 3 = about 1Kwh. Depending on where you live & what time of day you run the compressor, that might be anywhere from $0.11 - $0.60 at current prices that I am aware of. If you run a 120vac motor for 30 minutes at 30 amps, that’s 120 x 30 / 2 = not a big difference.
Now lets take a glimpse at maintenance. If you figure in a $600 valve kit every 500 hours, along with a quart or two of oil & a little time, that’s about $700/500 = $1.40 per hour or maybe $0.50-0.75 per fill.
If you buy cartridges, that might be -
$2.50 filtration + $0.25 power + $0.75 maintenance = $3.50 cost of fill.
If you load your own cartridges, you might be able to knock about a buck to a buck & a half off of that.
If you compare that to paying $6/fill, you are saving maybe 50%. If I figure in my cost of gas to drive to & from a shop that is 45 minutes away, in my truck that gets poor gas mileage, the advantage improves.
If you use 4 tanks per week, that’s roughly 200 tanks per year. At a savings of 50% on a $6 fill, that’s about $600/year in savings. At that rate, a $3k machine would take 5 years to pay you back, if you assume that the machine is trash at the end of that time. If the compressor still works, then you are further ahead by the resale value of the compressor.
Again, these are just ball park numbers for consideration. Your mileage may vary.
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