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Guidance to air compressors

Xyphota

Xyphota

Ultra Member
So for the sake of discussion, lets assume that I've never seen an air compressor before, I just know that they suck in air, put it into a tank, and then the tank feeds various tools.

I want to get an air compressor to potentially use the following tools:
Finger file (Ex: 40320 Dynafile II, 28.0 SCFM, Pressure of 90 psi)
Pneumatic Chamfering Tool (Ex: KBC Pneumatic Hand Chamfer Tool, 7.7 CFM, Pressure 90 psi)
Plasma Cutter (Ex: A40i Plasma Cutter, 6.7 CFM, 75 psi)
(Note*, I listed the above tools because they list all their specs, I'd likely be procuring cheaper alternatives lol)

What should I be looking for? Is it as simple as matching the CFM and pressure requirements? Is there a factor of safety that should be considered? Used vs New? 1 stage or 2 stage? Capacity? Any configurations that should be avoided at all costs?

And other considerations about air quality as far as moisture, temperature, and cleanliness are concerned?
 
Also, is there a calculator for estimating the effective run time of an under-specced air compressor for a given tool? Perhaps I'm not using the right search terms, but I can't find anything lol.

Like for an extreme example, a 5 CFM compressor with a 5 gallon tank with a max pressure of 125 psi could technically feed a 28 CFM, 90 PSI finger file for a few seconds, and then you could wait for it to recharge and use it again for a few seconds. Obviously this is an extreme case to emphasize the point, but It would be nice to know If I could estimate what tool use would look like, for a finger file with say a 7CFM, 150 psi max, 40 gallon compressor. (i.e. Would I get 5 mins of use, then wait 10 mins to recharge etc.)
 
Xyphota said:
Also, is there a calculator for estimating the effective run time of an under-specced air compressor for a given tool? Perhaps I'm not using the right search terms, but I can't find anything lol.

Like for an extreme example, a 5 CFM compressor with a 5 gallon tank with a max pressure of 125 psi could technically feed a 28 CFM, 90 PSI finger file for a few seconds, and then you could wait for it to recharge and use it again for a few seconds. Obviously this is an extreme case to emphasize the point, but It would be nice to know If I could estimate what tool use would look like, for a finger file with say a 7CFM, 150 psi max, 40 gallon compressor. (i.e. Would I get 5 mins of use, then wait 10 mins to recharge etc.)
Click to expand...
Maybe this?
 
I think air tools are generally pretty crummy. I've got a bunch and the electric or battery equivalent tools are more effective, don't have an annoying hose, and are far quieter tools. And yes you need an air dryer of some sort or you will get moisture flowing through the tool. Budget $200 or 250 for that to get something effective. Mostly or generally in my opinion air is good for cleaning off stuff and pumping up tires - and paint spraying. I have a cut off wheel tool which claimed 4 or 5 SCFM. nah more than that - I'd say 50% more at least. It's not an effective at all, runs for a few seconds and empties the tank so much it then is no longer effective. This is with a California air tools 3.8 SCFM 20 gallon compressor. It may be that the tools themselves are stating the air requirements ok but the compressor makers are not stating what it can do accurately. I also bought a big 60 gal 5 HP 240V 30 amp compressor (it's as tall as me) so I can run the more hungry air tools. About those - I also have a few right angle die grinders - one regular and one 'quiet'. The regular one when I run it my spouse immediately texts me and ask what the heel am I doing the neighbours are going to come over with pitch forks. It's shrill and very loud. The 'quiet' one I bought at twice the price is quieter but it's still plenty loud. Hearing protection is a must and the tools vibrate in your hands. Instead I now have two M12 battery right angle Milwaukee die grinders. They are a joy to use. Quiet, effective, no hose and no super expensive compressor required.

This big compressor I bought won't run 28 SCFM to operate that finger sander you linked to. No way. Find an electric one. I think air tools are more useful in a factory or big shop where there is a massive compressor for a big shop air system.
 
Just a few points @Xyphota, I'm no compressed air guru. But I've had various compressed air systems for 50 years and only a few were inadequate learning experiences.

First, the CFM for most tools, tanks, and compressors is standard atmospheric temp pressure. The universal gas law is PV=nRT. From this you can calculate stuff like how long a tank can supply a given tool or application. The universal gas constant applies to all gases but depends on the units used.

You can use the values
R = 287 (J/kg·K) or
R = 0.0821 (L • atm/ mol • K) OR R = 8.31 (J/ mol • K)

In most cases, you don't need to use R or n because they cancel out.

I think you should always get a compressor bigger than you think you need. It's amazing how fast you can drain a small tank and it's equally amazing how long it takes to fill.

I sized my last system to handle spraying paint because that was the most demand I could ever imagine needing. Not only that, but spray guns are pretty well labelled for realistic demand. I don't paint large things so even at that I was conservative. I say this mostly to point out that buying something to run regular air tools will leave you standing there with a silly look on your face if you ever decide you want to paint something of significant size.

Prolly the least consideration most users give is to size the Valves and Hoses correctly or even adequately. Hoses and fittings will bring a beautiful system to its knees in seconds. Everything is only as good as its weakest link.
 
David_R8 said:
Maybe this?
Click to expand...
Ultimately I'm trying to calculate duty cycle, but I guess to be more specific I'm asking for a calculator to help me estimate each of the terms in that equation.

@Janger All good points, and it may be true that running a pneumatic finger file is unrealistic in a home shop, but the pneumatic one spins twice as fast as the electric one and is lighter. I personally don't mind cords. For someone who exclusively works in the garage, the only tool I think is justified in being battery powered is an electric hand drill because its used so often. Every other tool in my shop is used infrequently enough that plugging it in is not a big deal IMO. I completely understand the appeal of battery powered tools if you are working on a jobsite or something like that though.

I need a compressor to run a future plasma cutter anyways so if I can kill two birds with one stone, might as well give it a go lol.

@Susquatch thank you for bringing up painting, that is an avenue I'd like to explore in the future and it's air requirements have not even crossed my mind while researching air compressors lol.
 
Direct from the Campbell-Hausfield website:
“How do I determine what size of air compressor to buy?

For best results, consider the tool that you anticipate using with the highest scfm rating and purchase a compressor with an output of 1.5 times that rating. For example, if you plan to use an impact wrench that requires 5.8 scfm, you would want to purchase an air compressor that puts out at least 8.85 cfm. If you plan to supply multiple tools simultaneously with compressed air, add the scfm requirements for all air tools and multiply by 1.5.”

Link:

That 28 scfm finger file is a hog. 28 x 1.5 = 42 scfm at 90 psi is way beyond the ratings of all the machines I see at Princess Auto, KMS or Peavey Mart. You’re looking at a pretty serious industrial machine.

If you’re only going to use something this hungry for a few hours a week, you could get by with a smaller compressor and just being aware of your run times relative to your machine’s duty cycle. That might work for an owner/operator, but probably not if you’re feeding a shop with employees running the tools.

I haven’t done the math, but I’m pretty sure you’re going to need some large bore hoses to deliver 28 scfm at 90 psi I doubt you’d push that much air through 50 feet of 1/4” ID hose and a handful of fittings unless your receiver is running at over 150 psi…

It seems to me, most shops are quickly moving away from air tools. The battery powered tools are just so much more convenient, cleaner, quieter, and probably cheaper if you take into account the cost of the compressor, dryer, air headers, electricity for the compressor, etc.
Sandblasting & painting are the two tasks where compressed air still wins IMHO.

As a general note. Compressors are inherently inefficient machines. More energy (electricity) goes into the heat generated during compression than is actually stored in the compressed air.

EDIT: You posted while I was typing. From your comments, I see some of my post isn’t really helpful.

This approach should allow you to calculate your duty cycle..

math.stackexchange.com

How can I calculate the running time of my compressor knowing the CFM rate of the compressor motor, tool, and tank size?

So, I actually have a real world application for the things my calc teacher tried to shove into my head, unfortunately it's been ten years since I took the class, and it all leaked out. That being...
math.stackexchange.com math.stackexchange.com
 
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Picking an air compressor often results in a poor operating air tool(s). Keep in mind air compressor ratings are based at a certain air pressure, eg. 10 cfm at 90 psi, supposedly this will operate an air tool needing 10 cfm at 90 psi. Maybe at sea level with air tem. of 68 degrees F., with a clean filter, turning at rated rpm, air humidity at 40% and so on. This will mean once tank pressure drops to 90 psi the compressor will need to run constantly to operate air tool. Most do not have turn on pressure set at 90 psi.
Does your air compressor put out the 10 cfm at 90 psi? How about at 3500 ft. Elevation? Not likely.
There is a rule of thumb somewhere, damed if I remember. I think it was, pick cfm for highest rated tool useage x 1.5 at rated pressure plus 10 psi. Eg. Finger file, 28scfm at 90 psi, compressor - 42 cfm at 100 psi. Note, there is not always a direct cross over between scfm and cfm!! This would possibly let compressor shut off while using tool. Otherwise, get a large tank, which will allow some run time.
 
Like it has been stated, battery tools are taking over, most mechanic benches now days have electric impacts/watchets etc...but battery's don't replace everything

forget about buying a compressor that will keep up to that dynafile, 28cfm is serious, anything you will want to buy/can afford wont be able to keep up, running it for short stints would be ok on 60g, but its going to drain that tank fast, and you will need to take breaks

if you have the money i would buy one of the standard 220v 60g uprights that everyone sells, it will keep up to the majority of tools, paint, run the dynafile on short stints, sandblast on short stints, it wont leave you with any regrets, and last you a very long time

because those 60g uprights are so popular you could find one used pretty easily, most just sit in a garage and pump up tires and run the occasional impact wrench....low use

the moisture issue is less prevalent with larger compressors (60g and up), the cheapest and easiest solution is to have a long 10 or 20 foot run of copper at a gentle downslope with a water trap at the end before your outlet, it will allow the air to cool and the water trap to do its job, that will take care of most if not all moisture problems you may encounter
 
I'll admit I have a 3/8" air ratchet and even used it to do some disassembly and assembly on the tractor this last week. The 1/2" drive impact wrench is close to 40 years old or more and it also was used this week.

Tools not used as much are the air nibbler, air chisel, Right angle mini grinder and 3/4" air drill. The air drill was bought on a whim and fills up space in the drawer. The grinder is tougher than my Dremel. The air nibbler floats through stainless that my 3-1 shear/brake/roller won't touch. And the air chisel has seen use over the years on various projects.

I have a small Makita battery drill (non-removable batteries) that was used to drywall my basement in Edmonton. With one of those dimpler screw driver bits. I'd have to recharge it do something else. Then go back to dry walling. Since this was DIY work it wasn't a big deal. If I want to use this drill now I have to buy new NiCAD batteries and solder them in. The old ones won't charge.

Similarly my electric impact driver was bought from house of tools and once the batteries failed they weren't replaceable without taking the packs apart. Even though I had two packs they were only available as special order from Home Depot and more expensive than a new drill/impact set. Same with my first Sears Craftsman electric drill. So I bought a replacement set of tools with chargers and packs.

I've never quite figured out why early on, a set of standards weren't set out and enforced for tool battery packs. D Cells, C Cells and AA cells are from the 60's so more than 50 years and you can still get a battery for something that uses those. Not so for tools that are now considered throwaway.

The number of times I use the 3/8" air rachet would likely mean I'd have to buy a new one because the batteries in the old one were toast. But yes, I wore hearing protectors when I used the air one.
 
Janger said:
I think air tools are generally pretty crummy. I've got a bunch and the electric or battery equivalent tools are more effective, don't have an annoying hose, and are far quieter tools. And yes you need an air dryer of some sort or you will get moisture flowing through the tool. Budget $200 or 250 for that to get something effective. Mostly or generally in my opinion air is good for cleaning off stuff and pumping up tires - and paint spraying. I have a cut off wheel tool which claimed 4 or 5 SCFM. nah more than that - I'd say 50% more at least. It's not an effective at all, runs for a few seconds and empties the tank so much it then is no longer effective. This is with a California air tools 3.8 SCFM 20 gallon compressor. It may be that the tools themselves are stating the air requirements ok but the compressor makers are not stating what it can do accurately. I also bought a big 60 gal 5 HP 240V 30 amp compressor (it's as tall as me) so I can run the more hungry air tools. About those - I also have a few right angle die grinders - one regular and one 'quiet'. The regular one when I run it my spouse immediately texts me and ask what the heel am I doing the neighbours are going to come over with pitch forks. It's shrill and very loud. The 'quiet' one I bought at twice the price is quieter but it's still plenty loud. Hearing protection is a must and the tools vibrate in your hands. Instead I now have two M12 battery right angle Milwaukee die grinders. They are a joy to use. Quiet, effective, no hose and no super expensive compressor required.

This big compressor I bought won't run 28 SCFM to operate that finger sander you linked to. No way. Find an electric one. I think air tools are more useful in a factory or big shop where there is a massive compressor for a big shop air system.
Click to expand...
I wasn’t impressed with the cordless tools until I talked to the manager at a bolts plus. He showed me the different sizes of batteries Milwaukee offers, and the newer, higher powered, batteries make a huge difference. The tool has more power and runs longer on a charge.

I won’t switch over because I have all air tools, but yes I hate cords. You get an extension cord, a trouble light cord, an air hose and torch hoses out for a job- forget it. Trip on everything, get tangled, creeper doesn’t roll, it’s maddening.

When are they making cordless oxy-propane rigs? :D
 
Chicken lights said:
I wasn’t impressed with the cordless tools until I talked to the manager at a bolts plus. He showed me the different sizes of batteries Milwaukee offers, and the newer, higher powered, batteries make a huge difference. The tool has more power and runs longer on a charge.

I won’t switch over because I have all air tools, but yes I hate cords. You get an extension cord, a trouble light cord, an air hose and torch hoses out for a job- forget it. Trip on everything, get tangled, creeper doesn’t roll, it’s maddening.

When are they making cordless oxy-propane rigs? :D
Click to expand...
I think someone makes a wireless TIG pedal.
 
Xyphota said:
So for the sake of discussion, lets assume that I've never seen an air compressor before, I just know that they suck in air, put it into a tank, and then the tank feeds various tools.

I want to get an air compressor to potentially use the following tools:
Finger file (Ex: 40320 Dynafile II, 28.0 SCFM, Pressure of 90 psi)
Pneumatic Chamfering Tool (Ex: KBC Pneumatic Hand Chamfer Tool, 7.7 CFM, Pressure 90 psi)
Plasma Cutter (Ex: A40i Plasma Cutter, 6.7 CFM, 75 psi)
(Note*, I listed the above tools because they list all their specs, I'd likely be procuring cheaper alternatives lol)

What should I be looking for? Is it as simple as matching the CFM and pressure requirements? Is there a factor of safety that should be considered? Used vs New? 1 stage or 2 stage? Capacity? Any configurations that should be avoided at all costs?

And other considerations about air quality as far as moisture, temperature, and cleanliness are concerned?
Click to expand...
I have the chamfering tool about 3years now, love it. Bought mine from Amazon well before KBC was selling them (yes they are identical to the "T", good thing KBC sells the cutters). Yes these burn air but they make bevels fast and neat. I use mine on Aluminium only for the products I make.

Amazon still sells them cheaper.

Initial setup takes a time, but once it's set, it's good. Haven't touch the set up since the initial one.
 
The problem with air in a tank, with out steady recharge, the pressure drops as air is removed, eg. a 60 cubic foot tank at 150 psi, remove 30 cubic feet of air, now it has 75 psi. Will your air tool work good enough at 75 psi for you? The finger file removed 28 cubic feet in 1 minute, call it 30 for easy math, 1 minute of user time, is this enough to do something with tool? I can't answer that part, and you want a regulater set to 90 psi otherwise air use is even higher.
Can you wait while compressor refills tank? The home/hobby shop maybe can, the production shop, likely not so much. A kind of short answer for many users, it's what you have, it will work, kind of. Me, I think I would see if the finger file will work well at 75-80 psi regulated,get a large storage tank, maybe 2 ganged together, pump it/them up, work for 1 plus minutes, go do something else for 5-10 minutes, then file for another 1 minute.
NOT really. Time to find a lower air user. Most likely electric. If you are useing a plasma unit, you don't want to stop in the middle of a short cut. You want good clean, dry air for that plasma unit and for painting also, and really for all air tools. Makes life easier. The cost can hurt.
Take this for what it's worth, look at the others notes, what might work for you? Maybe find someone with that 28 cfm finger file and try it, see what they do, use it for, what powers it. Any thing useing over 7 cfm at 90 psi is starting to get serious.
 
I was curious so played with some numbers.
Assumptions:
Air usage: 23 scfm
Compressor pump capacity: 30 scfm (note, this is probably at least a 7.5+ HP compressor)
Receiver (tank) capacity: 60 usgal (8 cu.ft.)
Compressor start pressure: 100 psig
Compressor stop pressure: 150 psig.

While using the tool,
Time between compressor stop and compressor start: 70 seconds.
Time from compressor start to compressor stop: 229 seconds.

Duty cycle = 229/(229+70) = 77%

These are approximations (I assumed the compressor output is constant at 30 scfm), but should be close enough…. Gives an idea of the size of machine you’d need to run a tool that needs 23 scfm. Short answer, a BIG one.

This machine should do it, based on its rated capacity. It’s rated at 100% Duty Cycle, and would need to be because it would be running at very nearly 100% when using the finger file…
www.kmstools.com

Ingersoll Rand 7.5 HP 80 Gallon Two-Stage Air Compressor

Designed for heavy shop or industrial use, Ingersoll Rand electric-driven two-stage air compressors provide the reliability and performance that are ideal for most applications and users including automotive service and body shops, fleet maintenance, mach
www.kmstools.com www.kmstools.com

I reality, if you use the safety factor of 1.5 times the tool consumption, this compressor would still be too small.
 
Lets just say I have an old pump mated to 5HP motor and 80 gallon tank. Two stage. Pump could spin faster - I think over 7.5hp if needed. Lowest is around 3.5hp.

If I remember correctly air produced is under 20 cfm at 90PSI.

I have around two dozen air tools. I even used with sand blaster etc. I so far did not run out of air. I do have project #1000 where I have old compressor head that I just mount with a motor to add as an addition (i.e. to pump into the same tank). In case of say needing to sand blast a lot.

I would think that for occasional use of a finger file above would work just fine, no issues at all.

I would use a much bigger compressor if I needed to use the finger file every day at actual work. Or did every day some sand blasting etc.

To summarize a 2 stage true 5hp compressor is a LOT of air.
 
I’m not going to wade into the math but I’ll throw in my two cents.

I have an air dynafile that I use at home. It’s an amazing tool for building bicycle frames. The electric ones are bigger, have less power and die pretty quickly. I bought mine used and it is a dynabrade brand one so I can’t comment on the other brands of air ones.

I don’t use it a lot but when I need it it’s great. I have a pretty cheap and not that big compressor. It’s a 26g 2hp mastercrap thing. The compressor obviously can’t keep up but the tool is still usable. I’d ball park the duty cycle at 20-30% maybe? Still beats files and emory cloth by hand.
 
Interesting,

The correct question isn’t; What’s your duty cycle? it seems to come down to; What’s your actual average air consumption?
Running the tool at half throttle doesn’t use 23 cfm, and if you run it for 2 minutes and it sits for 3 minutes, consumption is not 23 cfm on average.

Other than relying on people’s experience, I know of no way to determine the correct answer. Watching a shop full of workers stand around waiting for the compressor to catch up wouldn’t be much fun. Neither is buying a compressor that’s 3 times larger than necessary.
 
jcdammeyer said:
I've never quite figured out why early on, a set of standards weren't set out and enforced for tool battery packs. D Cells, C Cells and AA cells are from the 60's so more than 50 years and you can still get a battery for something that uses those. Not so for tools that are now considered throwaway.

The number of times I use the 3/8" air rachet would likely mean I'd have to buy a new one because the batteries in the old one were toast. But yes, I wore hearing protectors when I used the air one.
Click to expand...
My first rechargeable screwgun was bought in 1982, they have been around a long time. That one was Skil brand and was 6 volt. The problem with making 'standards is that it throttles innovation. Now we are up to 50 volt tools and they are remarkable. Also among the changes are things like brushless motors(3 phase) that produce more power and eat less. These are not like old combination wrenches, they need to change to keep up.
 
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