Air Compressor Size?

[cfk]

I am needing an air compressor for my shop, and I'm unsure of my size needs. Most of my tools are cordless so the majority of my compressor usage will be airing up tires on vehicles/utvs/mower, and blowing off my lawnmower, radiators, etc..

I'm (currently) torn between two - One is a 30-gallon rated at 6cfm@90 and 7.7cfm@40. The other is a 20-gallon rated at 5cfm@90 and 6cfm@40.

The smaller one is $100 cheaper, 10" shorter (fits under the staircase better), and almost 20 db quieter.. but I'm wondering if I'm going to miss the extra cfm.

I know bigger is usually better, but I'd love the smaller and quieter one if it will fit my needs..

 

[pattenp]

Unless you use high volume air tools the smaller one should be fine. It all depends on what you need to use in for. I just don't like the oilless ones.

 

[ycgoat]

For pumping up tires the smaller compressors are just fine, you just may have to move a little slower if you have multiple tires flat.

 

[Imatk]

I have a Hulk 30 gallon (Emax compressor) and it's great. Had it for 4 years now and it's been flawless. It's very quiet (oil less) and has decent CFM.

I can even paint small panels on my car projects.
I run an impact gun on it just fine, and a grinder just fine although it does need to play catch up if I'm using it a lot.

 

[nadogail]

I am sure you will appreciate the smaller and quieter more than you will miss the higher capacity.

 

[u2slow]

I have been really happy with a 3hp/10cfm/240V 20gal portable the last 20-some years. Mine is a Speedaire, but CH makes one too.

I recommend belt drive and oil-lubricated for long life.

edit: I have another $100 cheapo compressor I keep in the garden shed for bike tires, brad nailer, and blowing off dirty things.

 

[Toolmaker51]

With room under staircase, opt for the smaller compressor + a reservoir, long as it is a pressure rated vessel. Branch it into a manifold, and bypass, shut off for blowing down floor or doing tires, draw from reservoir running air tools.

1] Here, eventual air setup will be 80 gal 3 ph general shop compressor with simple manifold for rubber lines (incidental use) + branched 80 gal reservoir. There is use of air tools, pneumatic vacuums, small venturi generated vacuum chucks, bar feeders, cold air nozzles, H-frame press and so on.
2] Never blow down machine tools or grinder chutes.
3] I'll use a decent pancake for tires and portable air; that can pre-fill from shop air. A tank separator plumbed to each vessel for remote drainage, a wall trap at head of air lines. Even with dry air, it never hurts adding drain **** at 90° risers, with stepped or inclined progressively lower towards terminal end of lines.
4] Use plenty of pipe unions, ball valves and dope every fitting; always something adding to original layout. The ball valves are appreciated when a rubber hose parts, by shutting down a branch.
5] With a choice, use NPT barbs as connectors to rubber, not couplings. They all leak a little bit. Doesn't pay to buy electricity and plumbing to have lost adequate air by next morning.
6] Copper lines stay clean longest, the aluminum push-fit is used in lots of big installations but needs carefully prepared connections and mounting. By insuring dry air, black or galvanized pipe are common first choice. If lucky, you'll score a batch of brass couplings, they take much longer to corrode and seize.
7] While a lot of guys do, best to avoid PVC. It can shatter into projectiles when stressed.

 

[finn]

Sounds like one is the newer “silent ” design first popularized by California Air.

They seem to be taking over the low end compressor market for homeowner use. I haven’t heard anything terrible about them, but don’t expect thousands of hours out of it like a semi commercial Champion or Quincy.

I seriously considered one a couple of years ago. Everyone is selling a variation under their private label now, and the typical homeowner duty cycle doesn’t overtax the. Low noise and low cost, with adequate output is their selling point.

I actually ended up with a thirty gallon or so two stage Kobalt on clearance. Oil lubed and quiet, but louder than the “quiet” compressors, and not as much flow, but it should last longer.

 

[Toolmaker51]

In reference to compressor noise, the common remedy is a housing. Seen [more accurately, not heard] simple plywood boxes line with egg-crate flats. They hot glued each 'point' to the wood, though I figure isolating them a distance from the wood be an improvement. it's all about breaking and absorbing sound waves. Foam would work but collects dirt aplenty.
Most important feature is an inlet and outlet for air circulation to cool the cylinder. A pair of open weir type baffles, one low, one higher does the trick.

 

[thebmrust]

This is a first… most responses saying “go smaller”.

 

[Toolmaker51]

Home shop wise, smaller is acceptable; IF capable delivering 1.5x the consumption of your largest pneumatic tool (CFM), and sufficient pressure to operate trigger fired tools repeatedly. A reservoir is one solution.
The answer lies in three parts, requirements are first, undersized is pointless.
Second is footprint/ available cubic space.
Third, tips the scale; resources, the financial element.

Comment was directed at sound being part of the choice; easiest to moderate of all.

 

[CraigStu]

I got one of these a few months ago.

https://www.lowes.com/pd/CRAFTSMAN-30-Gallon-175-Oil-Lubricated-Portable-Air-Compressor/5000042449

It is not a new quiet compressor but it is a lot less noisy than the 35 year old one it replaced. There is probably a better term that I can't think of but it is a much softer sound. The old one was a 20 gal tank and it did everything I have ever needed except I did have to wait some times when using an air file or die grinder. Since it is all just hobby use, the waits were not much of a problem.

 

[smackey05]

I'd go larger. If you aren't using it much, I wouldn't expect it to cycle that much and cause a headache. If you ever decide to add other tools that require more air, you will be happier. I'm sure the smaller one will work fine for your use right now. I'm running one of those smaller california air ones in my workshop and a larger one in the garage where I actually do car work.

 

[Metal-Marc]

Go as big as you can afford.

 

[BillK]

I have a Craftsman 20 gal 2.5 hp compressor that I bought right after I got married in 1973. It has done everything I have ever needed at home including painting my Wife's 70 VW years ago. I am not a big fan of air tools so it does not get used for that very much. Pretty much the types of things you are talking about doing. I think something similar is all you need.

 

[dougf]

I would always say go big if finances allow, but consider my story...

I scraped and saved to buy a 60 gallon Husky compressor back in 2005-ish. Bought all the air tools needed for metal working along the way. Used a cutoff wheel a decent bit throughout the years when I couldn't get into an area with a 4.5 grinder. Its mostly been a pain to move, taken up valuable floor space, and never been really used.

About 2 months ago I tried to run it off a generator that I thought could handle it (HF 8750) and as expected the generator bogged down, compressor motor failed to start and immediately smoked. I went and bought a cheap Craftsman pancake compressor and tucked it under my bench. Its been everything I've needed it to be, from filling up tires to blowing off benches and misc things like that.

Wish I had got something smaller long ago.

 

[CombatNinja]

Nothing you described requires anything beyond a little 2 gallon air compressor. Everyone telling you to get a huge compressor is either not listening to you or an idiot.

Edit: or both

 

[finn]

Nothing you described requires anything beyond a little 2 gallon air compressor. Everyone telling you to get a huge compressor is either not listening to you or an idiot.

Edit: or both

You’re possibly correct, but opt for something quieter than the traditional pancake compressor because of the intolerable racket they generate.

There are a lot better choices out there with lower noise levels.

I find that I don’t use the pancake solely because of the noise, with the form factor making it somewhat difficult to move a distant second.

 

[CombatNinja]

Noise is a consideration with compressors but I don't think it looms large for his use case. He wants to inflate tires and blow dust off of stuff. That takes anywhere from 30 seconds to 5 minutes of use. I usually try to find something with oil as they tend to be quieter. This is the one I have:


4-gallon Ingersoll Rand for about $350 at Northern Tool after coupons. It is reasonably quiet and should last a lifetime with minimal upkeep. Not for everyone in that it weighs about 75 pounds and doesn't have wheels. I'm a pretty strong SOB so I just pick 'er up with one hand and move it where I want it but I can see that being an issue for a small guy or someone getting up there in years. That said, I keep it under my bench and have a 20' hose that can reach 75% of my floor space so it does not move often. I have similar use case as the OP--keeping tires inflated, blowing water off a car I'm detailing, etc. I've run tools off of it and it does fine for a homeowner type project but clearly it wouldn't work for a pro roofer.

 

[mike93lx]

Noise is a consideration with compressors but I don't think it looms large for his use case. He wants to inflate tires and blow dust off of stuff. That takes anywhere from 30 seconds to 5 minutes of use. I usually try to find something with oil as they tend to be quieter. This is the one I have:

I specifically went for a noise-focused solution for intermittent use.

With low noise, I can bring the comp in the house to run an air nailer, or just keep it close by without it overpowering a conversation, etc. I don't have to hide it in a closet or run a really long hose to get it away.

Air the quietest options for portables are oil-free. CAT is probably the best known, but lots of brands are selling them now

 

[CombatNinja]

I was always under the impression that the oil-free units were noisier? Have I been wrong all this time?

 

[mike93lx]

I was always under the impression that the oil-free units were noisier? Have I been wrong all this time?

No. You aren't wrong. There is newer style that are very quiet. My 4.6 gal CAT is something like 60dB.

 

[CombatNinja]

I didn't realize there was some breakthrough in oilless engine tech recently. Never too old to learn.

 

[finn]

It’s largely an intake silencer that reduces the noise.

That said, I am sure the NVH gurus had input in the design of the base compressor.

No comparison to the teeth rattlers from the nineties.

 

[Shadowdog500]

If you are just airing tires and blowing things off get the smaller 20 gallon one. I had a 25 gallon 6CFM Craftsman compressor for about 25 years for airing tires and basic air tools (impact and air ratchet) and it was more than enough. The only reason I went bigger is when I got a sprinkler system and needed a bigger compressor to blow it out. More CFM is also good if you want a blast cabinet, sanding tools, or a paint gun.

I don’t know what brand battery tools you have, but I bought the Dewalt 20v tire inflator a couple years ago and love the thing for filling tires. It wouldn’t be able to blow off things, but their 20v leaf blower would.

 

[Citation]

It’s largely an intake silencer that reduces the noise.

That said, I am sure the NVH gurus had input in the design of the base compressor.

No comparison to the teeth rattlers from the nineties.

The air intake does make a big difference. If I take the intake muffler/filter housing off my CAT compressor isn't quite a bit louder but still "quiet" compared to a typical 120V compressor. In addition to the air intake, the CAT compressors are slower turning vs most direct drive compressors. Note that motor RPM doesn't always equal pump RPM, even with some of the compressors where the motor and pump are an integrated unit.

Anyway, the CAT uses a 4 pole induction motor that directly drives the pump at around 1700 rpm. My direct drive Emglow roofing compressor also uses an induction motor but it's 2 pole and spins at around 3500 rpm. Some oil free compressors use universal motor, typically with a belt and reduction drive. I'm guessing the motor RPM in those compressors is quite a bit higher than 3500 RPM based on the use of a reduction drive. Universal motors are powerful for their size but also louder thanks to the brushes. So some of the older oil free compressors had pumps that were likely running faster than the 3500 rpm of a direct drive 2 pole motor.

The CAT compressor mounts the pump-motor assembly on rubber blocks and uses a braided line to the tank. A typical compressor is going to hard mount the pump to the tank and use a copper/aluminum hard line from the pump to the tank. Both of these things help transfer vibrations from the pump to the tank where it can ring like a bell.

Basically the people who came up with the quiet compressor design that CAT made famous (though I first saw an identical unit sold as a GMC Cyclone compressor... I'm sure GM was not pleased) decided to spend a bit of time trying to understand where all this noise was coming from.

As for the OP's question, I would probably go for the quiet compressor but I do have some questions. First, what is the tank pressure? 20 vs 30 gallons may not be that much if the 30 gallon runs at 135 psi vs 200 for the smaller compressor. In that case the 200 psi tank actually has more usable air. Most of the time the difference between the air capacity and flow rate of those two compressors won't be that significant. It would be a non-issue for things like an impact wrench, blow gun or filling tires. If you use a cut off wheel I could see the difference being significant. The low noise aspect really is nice. When my roofing compressor was my only compressor, I really hated when the thing would kick on because it really was noisy. I was glad it refilled so quickly. Conversely, the CAT compressor is so quiet I just don't care if it has to cycle more or takes long to fill. I will also say, putting the compressor in an otherwise unused space is that much better.

Finally, if you, on occasion, need extra flow/tank, tying two compressors together is an option if both compressors have the same blow off valve pressure (it's a safety thing) and you have a separate circuit powering both compressors. This would allow you to use the quiet compressor most of the time but if you did have a job where you needed that extra flow even a $100 Porter Cable pancake compressor would make up the difference in flow and most of the difference in tank capacity. The total cost would be similar but most of the time you get the benefit of quiet. However, you do have the hassle of setting up the two compressors when you need them.

One final comment, if most of the time you aren't going to need much air then the service life difference between oil and oilfree pumps should be a non-issue. If you are going to run this thing a lot then the pump life of an oil free vs oiled may be an issue. While the rings/etc can be replaced in most oil-free pumps, oiled pumps do last longer. An oil free pump may need a new set of rings/cylinders 10-20 years from now.

 

[cfk]

Thank you guys for all the replies! I think I'll go ahead with the smaller one.. I just have no frame of reference what 5cfm is vs 7 or 8, which is basically why I asked my question.

I have a 6 gallon pancake that I've used for nail guns and stuff for years, but it irritates me having to plug it in or move it around so I've always wanted to just have an upright one plumbed in to a hose reel thats ready to go whenever I want to blow the grass off the mower or cleaning out the radiator on the tractor..

 

[nadogail]

I saved my aluminum cans and worked a few side jobs to buy my first compressor, it’s a 20 Gallon oil less Devilblis (sp?) from a big box store. It is a noisy machine, but it does what I bought it for and I don’t owe any money on it. For small jobs away from my shop I take it 5 Gallon Twin Tank oil lubricated unit. Occasionally, maybe once a year I connect both machines together for those times I need lots of capacity.
My generator has run both compressors together and a saw.

 

[u2slow]

Thank you guys for all the replies! I think I'll go ahead with the smaller one.. I just have no frame of reference what 5cfm is vs 7 or 8, which is basically why I asked my question.

The cfm at 90psi is what matters for air tools. Real value is the $/cfm. HP ratings are too warped and exaggerated to go by unless you can really understand the level of machine you're looking at.

My little $100 compressor is a little 2-gal with a coiled nylon hose. I'm happy to pack that around to where I need it and run an extension cord. Hoses are more fussy to handle and coil/uncoil than a cord.

 

[oldmachinenut]

It’s largely an intake silencer that reduces the noise.

That said, I am sure the NVH gurus had input in the design of the base compressor.

No comparison to the teeth rattlers from the nineties.

I put a Solberg filter/silencer on my already quiet Quincy 310 and it made it noticeably quieter.

 

[nadogail]

Air Compressors seem to come in three sizes; Baby Bear (not big enough and very common) , just big enough or Mamma Bear (less common and subjective) or Poppa Bear (Big and too expensive).

 

[Lassen Forge]

I have a cheapy oil-less $60 pancake compressor for those kinds of jobs - blowing dust into my lungs, popping bicycle tires for the neighborhood kids, putting almost enough pressure into my "silver bullets" (water fire extinguishers) to get half the water out, and making my impact wrench do one good UggaUgg before it runs outof steam... didn't want to spend a lot on it as it's likely I won't need it beyond this year...

I had a pair of siamesed DeWalt 4 gallon units (long story short - bought one at HD, the overheat cutoff switch "broke", went to exchange it, they said no, but sold me one at their cost (about 60% off), replaced the OH switch and now I had 2...) and that threw all the air I needed - I'd still have to wait for it to regenerate every few minutes, but it was survivable...

Had I the money, I would have bought a rotary vane compressor, pricey but all the air you could ask for, and quiet enough to have in the same room. Maybe the new shop...