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Old 10-12-2011, 10:54 AM
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Quote:
Originally Posted by oldred
Honestly that is a serious mistake, a marginally performing compressor is the WORST case for a bigger tank! The (mis)logic behind a larger tank is in thinking it will extend run time but that is not thinking beyond the first recharge cycle at which point ALL extra time gained will then be lost to the proportionally longer recharge time so nothing is gained. Usually a compressor with a larger tank will be mated to a higher CFM compressor but the problem is that is not always true, selecting a compressor by the size of the tank can easily cause a person to pass up better performance for a uselessly over-sized tank. As I pointed out earlier the difference in run time between an 80 gallon tank and a 60 is going to be mere seconds anyway then the tank has to recharge and even that extra time is lost waiting on the longer recharge time for the larger tank to refill (with all else being equal), if the compressor keeps up then no waiting will be required but again in that case the tank makes zero difference in performance. With equal CFM ratings a 60 gallon tank will average the same run vs recharge time as an 80 gallon tank, heck if the CFM is the same even a 40 gallon tank would keep up just as well but the cycle rate might be annoying. For that matter a 40 gallon compressor with 13 CFM would OUTPERFORM a 12 CFM compressor with an 80 gallon tank! It's easy to find compressors with 60 gallon tanks that will outperform some 80 gallon models and that's why telling someone to look for a big tank is terribly misguided advice. CFM is what makes a compressor keep up and a few gallons of extra tank storage only changes the cycle rate and does not help at all to keep up with air hungry tools, over a given work period the run time vs the time spent waiting on recharge will be exactly the same between 60 gallons or 80. The larger tank will yield fewer but longer recharge cycles but the average run time will be the same if all else is equal. Select that compressor based on SCFM and overall quality because it is how much CFM the pump is putting into the tank that matters not how much the tank can hold!



I am not saying to avoid big tanks, just don't buy based on the thinking that it's going to make a better performing compressor because it won't. The manufacturer will size the tank according to the PUMP/Motor and expected usage demand so that the run and recharge times will be reasonably balanced, NOT to increase performance. On some cheaper models a large tank is used to create the appearance of being a large compressor but they may have small under powered pumps with low CFM ratings that mean they actually are in fact small compressors, some of those things would actually be better off with a smaller tank. The bottom line is for most home shops a compressor of adequate size will most likely be either a 60 gallon tank or an 80 gallon and either is just fine but that should depend on the CFM, in any case NEVER, EVER pass up higher CFM to get a bigger tank- NEVER! Buy based on CFM and duty cycle because that's what makes a compressor keep up and don't worry about a few tank gallons one way or the other!
Enough with the bashing already, just give the man the recommendation he asked for! After all, you ARE the expert here. You've wasted a bunch of time typing and still nothing of substance except your very critical opinion on tank size...


Russ
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