School Me on Air Compressors

[nahudson]

So I am wanting to get an air compressor, I am a DIY, however I want to make sure I have the right compressor for all of the jobs I want to do

I want to be able to use it for sanding, impact wrench, just airing up tires

What do I need to accomplish these things?

Basically, if I am using it for sanding or cutting, I don't want it to just last 30 second to a minute and then have to wait 5 minutes for the compressor to fill back up

I know little to nothing about compressors

 

[Davefr]

Look up the CFM specs on the largest air consuming tool you plan to use. If that tool has a high duty cycle then get a compressor that outputs at least that amount of air. (maybe add an extra 20%).

(ex: DA sanders are huge air hogs. My little Sioux 5" DA consumes >15CFM at 90 PSI and sanding is usually done at very high duty cycles. My 5HP/60 gallon IR compressor can barely keep up.)

Now if your willing to go electric vs pneumatic for these types of tools you can get by with a much smaller/cheaper unit. Filling tires can be done with a "toy" compressor. An impact wrench uses a fair amount of air but duty cycle is usually low because they're typically used in quick bursts followed by a few seconds of idle time. This will let an slightly undersized compressor catch up.

The bottom line is to start making a list of all the pneumatic tools you plan to use now and into the future and get their CFM specs in order to match up a compressor.

You also need to decide if portability is important and what kind of circuit you plan to use.

 

[Gary S]

LIke Davefr said. CFM. That is what really matters.

The CFM of the compressor needs to be well above the CFM of your tools, and remember that CFM of tools is usually measured with no load. A die grinder rated at 4 CFM will likely take 3x that when cutting. A DA sander is the same. A sander rated at 4 CFM will want much more than that when working under load.

 

[p0lar]

LIke Davefr said. CFM. That is what really matters.

The CFM of the compressor needs to be well above the CFM of your tools, and remember that CFM of tools is usually measured with no load. A die grinder rated at 4 CFM will likely take 3x that when cutting. A DA sander is the same. A sander rated at 4 CFM will want much more than that when working under load.

I'll reiterate this too.. CFM, CFM, CFM. You can have all the PSI and storage in the world, but if your compressor can't keep up, you'll eventually run out of air.

You'll really only be able to achieve ~6SCFM @ 100 psi reliably from a 115VAC circuit, so that's a reasonable point of demarcation between portable and stationary compressors. Once you jump up to a 230 VAC compressor, you can reasonably expect anywhere from 9 to 30 SCFM @ 100 PSI on a pump driven by a single phase motor before you have to switch to three phase, provided you're only driving one pump with one motor.

 

[GoodEnough]

In terms of cutting and grinding, what is the advantage of air powered over an electric unit?

 

[mebuildit]

Where are you located? I'm selling my 7.5HP 80 gal, 2 stage Champion. I'm in Az.

 

[mmouse]

Go big or go home.... If you want to blast, sand, or paint.

The minimum for what you are asking would be about 60 gallon and 10 cfm.

FYI, it is cheaper to use electric sanders, grinders, and sawsall, than run them on air.

 

[kingnba6]

good points in this thread. but i have a craftsmen compressor that has both 110 and 220. by upping to 220 will i increase cfm?

 

[Davefr]

good points in this thread. but i have a craftsmen compressor that has both 110 and 220. by upping to 220 will i increase cfm?

The short answer is no. The long answer is maybe just a tiny amount due to less power loss by going to 220VAC.

 

[Gary S]

good points in this thread. but i have a craftsmen compressor that has both 110 and 220. by upping to 220 will i increase cfm?

Usually no. Read the nameplate on the motor. It will likely show that you have the same HP on either 120v or 240v, so if the HP stays the same and the RPM stays the same, the CFM stays the same.

 

[kingnba6]

thanks. so looks like ill be sticking to my 110 circuit instead of running new wires for a 220.

 

[TK LP]

So I am wanting to get an air compressor, I am a DIY, however I want to make sure I have the right compressor for all of the jobs I want to do

I want to be able to use it for sanding, impact wrench, just airing up tires

What do I need to accomplish these things?

Basically, if I am using it for sanding or cutting, I don't want it to just last 30 second to a minute and then have to wait 5 minutes for the compressor to fill back up

I know little to nothing about compressors

Go big or go home.... If you want to blast, sand, or paint.

The minimum for what you are asking would be about 60 gallon and 10 cfm.

FYI, it is cheaper to use electric sanders, grinders, and sawsall, than run them on air.

For the past 26 years, I've used this compressor:





To operate these tools:



As well as run sandblasting equipment for several projects like this frame:



The only tool I've had trouble keeping up with is the red handle circular sander, although the manufacturer of the straight line sander list CFM requirements higher than my compressor, but all of the others it's kept up with. The blaster was a portable 60lb. hopper I've borrowed from a friend. I've also recently added a couple of low CFM HVLP spray guns.

While I agree wholeheartedly that with compressors, bigger is better, I also believe the if budget and/or space restrictions limit what you ultimately use, you can get the job done with less, and still achieve very professional results.

 

[theoldwizard1]

For the past 26 years, I've used this compressor:

Older is better in many cases ! It look like those CFM ratings are real !!

Today, to run a cut off wheel, die grinder, DA or a blaster I would recommend a 5hp twin cylinder and a 50 gallon tank.

My 2hp can't keep up with a cut off wheel for more than about a minute or two.

 

[Domus]

When I worked as a service engineer on air compressors, finished about 15 years ago but did 20 years, we always worked on 1 HP would give 4CFM. Smallest machine I ever worked on was a 4 CFM in a dentist's surgery, largest was a row of 6 x 600 CFM in a steel works.

 

[skruft]

You have gotten good advice above. The smaller compressors like the red one pictured are fine for all usual tools except those with air motors or big pistons that must run for a long time. These big air users are mainly the sanders or buffers used in bodywork, and also large commercial air chisels and scalers.

That is one reason why some people stick with electric sanders and buffers.

There are other air tools that use plenty of air, but only for a short time, like the impact wrenches and drills.

All the air nailers and drivers used with wood require little air.

Filling tires and blowing things clean can be done with smaller compressors.

 

[cheechi]

What is it you're sanding?

 

[bsaint]

Bigger isnt always better if you're looking to save money. Why fill a 120 gallon tank with 10 hp if you only use a 4 cfm air tool five times for your whole project?

Find out what tools you use. Most likely your average CFM is 5. Then figure your duty cycle. In one hour how many times will you use the tool? 5 minutes total? Your duty cycle is 8%. A 1hp compressor would suit you. Total of 15 minutes? 25% duty cycle. See what I am getting at? Unless you don't care about your electric bill.

 

[redsandman6]

I would add that the faster the motor/pump spins the higher the noise level the compressor will make. this is if the compressor is not in a cabinet or some type of enclosure.

 

[firebox40dash5]

Bigger isnt always better if you're looking to save money. Why fill a 120 gallon tank with 10 hp if you only use a 4 cfm air tool five times for your whole project?

Find out what tools you use. Most likely your average CFM is 5. Then figure your duty cycle. In one hour how many times will you use the tool? 5 minutes total? Your duty cycle is 8%. A 1hp compressor would suit you. Total of 15 minutes? 25% duty cycle. See what I am getting at? Unless you don't care about your electric bill.

Well, unless you'd like those minutes to be relatively close together, rather than evenly spaced throughout the hour. You're not doing much with a 1hp compressor and a 5cfm tool. A lot of tools are also rated no-load, and working cfm (such as impacting on a stuck bolt) is several times that, although that plays more into tank size to keep it fed for <1 minute than compressor power.

I don't really see the electric bill playing into it a whole bunch, unless you're draining it and filling it every day. A more powerful compressor ***** more juice for a shorter time, a less powerful one ***** less juice for a longer time. I doubt you'd notice the difference. I can tell you the electric bill at work is $200-300 a month with a 5hp single phase compressor... as well as 1200w of halogens on the wall and I think 3600w of halides in the ceiling, running 60+ hours a week. I don't think our compressor makes a dent in that, and I've had similar bills for a house (albeit with resistance heat).

 

[CodyY]

Can you? Yes.
Should you? Not always.

Just like anything else, go as big as you can comfortably afford. I currently have a 5cfm 60 gal twin cyl 5hp vertical. Its great for everything but when running a cutoff wheel or sander for LONG intervals I get tired of hearing it, or when running more than one air tool at a time. My new shop will probably be equipped with a 9cfm 7.5hp 80gal setup. However, I'm working full time in my shop and fabricating hot rods.

That being said, I worked from home for quite a while with a 23 gallon unit with a "sealed" pump. As long as I wasnt trying to run sanders and cutoff wheels it generally kept up. If you just need a decent compressor, go get the 299 special from Lowes or Home Depot.

Sent from my SM-T210R using Tapatalk 2

 

[bsaint]

Well, unless you'd like those minutes to be relatively close together, rather than evenly spaced throughout the hour. You're not doing much with a 1hp compressor and a 5cfm tool. A lot of tools are also rated no-load, and working cfm (such as impacting on a stuck bolt) is several times that, although that plays more into tank size to keep it fed for <1 minute than compressor power.

I don't really see the electric bill playing into it a whole bunch, unless you're draining it and filling it every day. A more powerful compressor ***** more juice for a shorter time, a less powerful one ***** less juice for a longer time. I doubt you'd notice the difference. I can tell you the electric bill at work is $200-300 a month with a 5hp single phase compressor... as well as 1200w of halogens on the wall and I think 3600w of halides in the ceiling, running 60+ hours a week. I don't think our compressor makes a dent in that, and I've had similar bills for a house (albeit with resistance heat).

I sold compressors for four years and never had a customer complain their compressor was too small or too big.

Don't forget, an electrical motor is an inductive load. The power company sees it.

Also I run an hvlp Satajet on a 3/4 hp Emglo just fine.