Minimum HP to generate 6 CFM
by Jerome
I want to calculate the minimum horsepower in order to create a 6 SCFM.
Do you have a calculation for it?
Bill answers...
Hi Jerome:
The rule of thumb for compressors and flow generation is that for every HP of electric motor, a compressor will generate about 4 CFM of compressed air at 90 PSI of pressure.
For smaller compressors under 10HP it's a bit less than that, so maybe figure on 3 CFM @ 90 PSI of compressed air generation for a 1 or 2HP motor.
What you don't say is at what pressure you need the 6 CFM, and that's critical. If you need 6 CFM at 250 PSI for example, you'll need a higher HP motor, and if the 6 CFM is at 20 PSI, then you'll be able to use a correspondingly smaller compressor motor.
Cheers,
Bill
Continued
I try to create a 100LPM suction pressure in my lab and I know 1 cfm is equal to 28.32 LPM.
However, I do have a 2hp compressor in the lab but the suction pressure can only go up to around 70 LPM.
The compressor that I have doesn't show the psi on it. Do you think I should get a 3-4 Hp compressor instead?
Hello again, Jerome:
If it were me, and I wasn't sure, I'd visit the local rental store and rent a larger compressor for the day to run some tests.
If you've only got 120 VAC in your lab, you will be limited on the size of compressor you can power with that voltage. A 120 Volt circuit can only power so many HP, and if your demand for pressure and volume exceeds that, you might need to move to a 240 VAC circuit to power a compressor big enough.
In any case, rent a larger unit than the one you've got that runs on 120 VAC from the local rental depot and test the supply and demand.
Take the guesswork out of it.
Cheers,
Bill
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Calculating usage
by Tom McCourt
(Boston, Ma.)
I currently have a Kellogg 45tv with a 10 hp motor, the tank is a b452bo. On @90 psi off @ 115.
Unit runs 4 min on and 3 min off during working hours.
3 on and 4 off during non working hours.
Can we calculate usage with this info ?
I know it runs hard. Is this the proper machine for this duty ?
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CFM question
Does the cfm figure relate to the air input or the air output when for example a machine states that it needs 8.4 cfm
Bill answers...
Howdy, and thanks for the question.
Generally speaking, an air tool or compressed air using appliance will indicate a consumption flow rate.
In your case, it's 8.4 CFM.
The flow rate will also demand a specific pressure; for example, 8.4 CFM @ 90 PSI.
Without knowing the pressure requirement, the flow factor is almost meaningless.
Now, to your question.
If you visit this page about SCFM and CFM it will answer your question in detail.
In simple terms, the flow demand of an air tool or air using appliance is generally referring to air that has already been compressed, and therefore, refers to air after the air compressor.
Cheers,
Bill
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CFM and PSI
by Chris R. Cardilo
(Pittsburgh, PA)
Which compressor do I choose???
Hi-
I have a piece of equipment that requires 25CFM @ 110PSI.
The specs on one 5 HP rotary compressor that I am looking at lists the CFM at 16.5 with the PSI at either 145 (50Hz model) or 150 PSI (60 Hz model).
Roughly-how much CFM would you get with either model at 110 PSI? Not sure that this 5 HP compressor is powerful enough for my equipment but I don't know how to figure this out.
Thanx!
Chris
Bill answers...
G'day Chris...
You don't indicate whether your demand for 25 CFM @ 110PSI is constant (as in 8 hours a day, five days a week) or intermittent; maybe running the application for 5 minutes, then later 10 minutes...and so on.
The reason that's important is that you can often get away with a smaller compressor if you've got a big enough receiver (or extra air tank) and your demand isn't constant.
That your compressor puts out 150 PSI is good. That means that you've got quite a store of 150 PSI air in the tank(s) when your compressor cuts out.
If your demand for 110 PSI flow isn't constant, then the combination of your 5 HP compressor and lots of air storage will do you just fine.
On the other hand, if your application is running continuously, then your compressor probably cannot “catch up” with the demand and shut down, or you'll see a continuously diminishing available air pressure until the supply of air to your application is too low to continue working.
The rule of thumb for air compressors over 10HP is that you'll get about 4 CFM of compressed air at 90 PSI for every horsepower of motor.
When a compressor is under 10 HP (your typical DIY model) I use the figure of about 2.4 CFM at 90 PSI for every horsepower of electric motor.
That beautiful compressor that you sent the picture of is a whole different matter. This looks like an excellent quality INDUSTRIAL type compressor, and I suspect it will deliver the 4 CFM @ 90 PSI that the rule of thumb suggests it should.
Your Atlas Copco probably is built for continuous duty (worth checking), meaning that it has been built to run and compress air 24 / 7 / 365.
So, to your original question...either unit will be very close in producing the flow you need. If your demand is constant, you might consider kicking it up to a 6 or 7.5 horsepower. If your demand is periodic, either the 50hz or 60hz should do just fine.
And, if you opt for the 5 HP unit that's lower cost than the 6 or 7.5 HP, consider throwing a few dollars at another air storage tank to help handle the demand when your application is running.
Cheers,
Bill
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PSI rating on an air compressor
by al
I wanted to know if there is a difference in performance when you have a 2hp 10 gallon air compressor rated at 125 psi as opposed to a 1.5hp 10 gallon compressor rated at 135 psi.I noticed that when I was shopping for an air compressor today.Also I noticed that the newer models that were oil less operated at 135psi,while the oiled ones operated at 125psi.Your info will be appreciated.
Bill answers...
Hi Al...
As a rule of thumb, an air compressor will generate about 3 or 4 HP of compressed air at 90 PSI for every HP of motor size. That is the "performance".
The size of the air tank, regardless of the motor horsepower, has no bearing on either the compressor performance or the pressure rating except in terms of available, pre-compressed air for your air tools to use.
The compressor pressure rating is determined by the company that builds the compressor. Their engineers have determined that the parts they use, the mechanical and electromechanical systems in their compressors, will be able to generate XX PSI of force.
When you say that the compressor will "operate" at a certain pressure rating (135 PSI for example) what that means is that when that compressor is turned on, the compressor will start to run and keep running until the pressure in the tank reaches that 135 PSI, and then the compressor turns off, until the pressure in the tank reaches the cut-in pressure.
When we use compressed air, we use the integral regulator to reduce the downstream pressure to the level required by the air tool or application.
Rarely does an air tool require 135 PSI, at least at the DIY level.
Whether you use an oil free or an oil lubed compressor is personal choice. If I were buying a new one today, I'd certainly opt for oil free, for a whole bunch of reasons.
What you want to look at is how much compressed air your compressor will deliver at the pressure you need it. The benchmark is usually 90 PSI or so, as that's the pressure level required by many DIY type air tools.
The higher the motor HP, the more compressed air that that compressor can deliver at 90 PSI.
Hope this helps....
Cheers,
Bill
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How do I compute the scfm of my air compressor?
I have a reciprocating air compressor, max discharge is 125 psig, 100 hp, 708 rpm, 12-7x7.
What is my scfm?
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SCFM claims for a new compressor?
by Humberto Borrego
How accurate are the specs given in the advert. for compressors?
Harbor freight has a unit # 92504 that claims up to 16 cfm's but I doubt it???
16.4 CFM @ 40 PSI, 15.7 CFM @ 70 PSI, 14.5 CFM @ 90 PSI, 13 CFM @ 110 PSI;
How can this be checked???.
Bill answers...
Hello Humberto...
The rule of thumb for compressors is that units over 10HP motor size will generate about 4 CFM of compressed air at 90 PSI...per horsepower of motor. Units under 10HP might generate between 2 + 3 CFM @ 90 PSI, depending on their efficiency.
A 10 HP motor driven compressor could be expected to generate about 40 CFM of compressed air at 90 PSI.
You don't indicate the horsepower of the unit that you are asking about...so it's pretty hard to say whether the flow and pressure claims make sense.
The problem with home compressors and flow factors is that most of them are being powered by 120 VAC house current, and...that means that they are limited in their output.
Energy cannot be created or destroyed, it can only change form.
With a compressor, you are converting electrical energy into compressed air energy, and the energy output (compressed air) is always limited by the input (volts from your supply to the motor).
Humberto, I can't tell you whether or not the claims are accurate. They certainly seem robust for a DIY type of compressor.
Regards,
Bill
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Increasing pressure for impact wrench
by Mike
Hi, I have a question about adjusting the air pressure with the regulator. I just bought a new compressor and tool kit and tested it out on one of my cars lug nuts. The instruction manual said the impact wrench operates at 90 PSI so that is what I set the regulator to. However I could not break the lug nut loose. Can I raise the PSI to remove the lug nut? Thanks for any help.
Bill answers...
Hello Mike:
What flow at 90 PSI? You could have a very low flow from your compressor at that 90 PSI, and that flow might not be enough to power the impact wrench to remove the lug.
Or, as you suggest, you can increase the pressure to try and make that happen.
If you choose to increase the pressure, make sure it stays within the wrench operating pressure range.
My guess is that you haven't enough flow, even at the 90 PSI to do the job. You get about 3-4 CFM of compressed air flow at 90 PSI for each horsepower of compressor motor size. What's the HP of yours?
Start on this page, and then follow the links to get more information on compressor sizing.
Or, get all of the information condensed for you in my ebook The Home Compressor. Information on that here.
Cheers,
Bill
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Can you tell the CFM from just the PSI?
by loz
(uk)
Hi,
Sorry this is probably a really silly question,
But is there anyway to calculate the CFM from the PSI rating on a compressor?
The reason I'm asking is because I've seen lot's of compressors for sale with only the PSI noted on it.
Thanks,loz
Bill answers....
Hi Loz:
In a word, no - at least not that I'm aware of.
It's too bad that there isn't a standard for labeling compressor outputs isn't it.
Check the label plate carefully, usually a compressor will show the PSI capability at a certain CFM. I'm surprised that yours doesn't.
Cheers,
Bill
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SCFM vs CFM
by Hugh Blackburn
(Joppa, MD USA)
F.Y.I.
You should give some more information on SCFM because many air driven pumps are sized by SCFM input.
Most manufactures use 70F and disregard humidity.
You should add the simplified equation:
SCFM = CFM x PSIA/14.7 x 530/T+460 and explain it so that people can do some simple estimations.
F.Y.I.
Bill answers...
Thanks Hugh.
It seems you've done an excellent job of doing just that.
Want to go a little further and tell folks what the equation 530/T+460 means?
Thanks,
Bill
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I keep getting 4cfm @ 90 PSI or 100 PSI or what?
by DAVE
(clovis, nm 88101)
I keep getting 4cfm @ 90 or 100 or? What is the standard? does it necessarily apply? is there a minimum hp? does it apply to all compressor types?
I am working on a tool design that requires a variable load, variable speed, full time, compressor.
I want 10.3 bar or better, and I want the horsepower demand to be a fixed % of the output hopefully, 1 hp per 4cfm @ 104 psi 1.25 @ 150 or 1.5 hp for 4 cfm at 200.
DOES SUCH AN ANIMAL EXIST?
Bill answers...
Hi Dave:
A lot of good questions.
When I'm "guestimating" compressor size, I use 1 HP equals about 4 CFM at 90 PSI. You see, most of my applications are fairly general, and the client wants to make sure they have enough air.
Like yourself, I've seen 4 CFM @ 100 PSI as a rule of thumb, as well.
I don't think that there's any standard, as every compressor manufacturer's product is different, and the efficiencies will vary accordingly.
As I understand it, the 4 CFM rule of thumb applies to compressors over 10 HP. Those under that size have less volume, and I generally use 2 CFM @ 90 PSI for every HP of motor for units under 10 HP. Again, I'm looking for margin of safety in terms of compressed air availability.
"I want 10.3 bar or better, (147 PSI +) and I want the horsepower demand to be a fixed % of the output hopefully, 1 hp per 4cfm @ 104 psi 1.25 @ 150 or 1.5 hp for 4 cfm at 200."
All I can suggest to obtain information about the horsepower being a fixed percentage of the discharge output is to email the manufacturers of the compressors you are considering, and pose the question to them. They'll have the engineering backup to give you the answer.
Cheers,
Bill
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Converting SCFH to SCFM
by Rod Henshaw
(Calgary Alberta Canada)
A machine I am working on calls for 350 SCFH (standard cubic feet per hour).
I am not sure if I just divide the 350 SCFH by 60 to get SCFM (standard cubic feet per minute) as there are 60 minutes in an hour.
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SCFM= Too low to run standard air tools?
by Jason Moore
(Grovetown, GA, USA)
My Compressor
My wife just bought me a craftsman vertical air compressor.
Being new and unfamiliar to air compressors we thought that the bigger tank allowed for a wider range of tools to be used efficiently and effectively.
To my dismay, and my wifes, we found out that our SCFM on our Craftsman compressor is only rated at 4.3 SCFM at 40psi and 3.3 SCFM at 90psi.
Our impact wrench, from Craftsman, uses 4.8 SCFM and my impact gun likewise uses far more SCFM than is rated for our compressor.
So I looked around and found that most air tools from almost every maker exceeds the ratings for my compressor. Is the do-it-yourselfer forced to pay $400-$1000 for a compressor that runs at least 10 SCFM to ensure that a variety of tools have enough air to run properly??
Thanks,
Jason Moore
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2.2 SCFM @ 90 psi = ?? SCFM @ 40 psi
by William Mckeague
(Redmond, wa, use)
If a compressor can put out 2.2 SCFM at 90 psi, what can it put out at 40 psi? Is it a linear calculation? i.e. (90/40)*2.2 = 4.95 SCFM @ 40 psi?
Bill thinks about it...
Hi William, how are things out in Washington?
I've had this question before, and frankly, I'm no further ahead today after doing a lot of research than I was six months ago.
Here's the thing.
A recip compressor has a piston with a fixed volume in the cylinder. Each time that piston cycles a fixed amount of free air gets compressed into the tank.
The compressor runs at a constant cycle rate, therefore, the speed with which it compresses air doesn't change.
If the compressor can pump out 2.2 CFM at 90 PSI, then the only difference between that flow rate and the flow at 40 PSI will be the speed with which the compressor tank reaches the 40 PSI? Follow me?
So, to my mind, I would expect there to be a guideline formula that allows us to plug in the different elements to come up with that flow rate.
I have talked to a number of folks much more in the know than I about air engineering, and have not, so far, come up with one.
I can't help you right now. I'm still looking. And I appeal to readers that might know the answer, please let us know.
Thanks,
Bill
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Increasing compressor CFM
by Brennan
(Santa Barbara)
Hi,
I was wondering if it is possible to increase the CFM on a compressor or if what you have is what you get?
I have a 25 gallon, 5.4 CFM. I would like to bump it up to at least 12 CFM.
Can I just swap out the regulator?
Thanks
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Converting CFM output
by Will
I've shopping for more tools and maybe a spray gun for my compressor.
My 30 gal. cobalt is rated at 5.7@90 and 7.0@40.
The problem is that many times tools and spray guns are rated @30, @35, or @50.
How do I convert these figures so I'm not comparing apples to oranges?
Bill answers...
Hi Will.
Very good question, and one that I will answer in the release of my upcoming ebook, The Home Compressor.
I've research to do to answer this, and will advise you when the ebook is ready to let you get in on the early-bird deal.
Thanks,
Bill
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What CFM is an Ingersoll Rand HP355WP?
by Martin
(london)
What CFM is an Ingersoll Rand HP355WP?
Bill answers...
Hi Martin...nice to hear from the UK.
First off, you can normally count on generating about 4 CFM of compressed air, at 90 PSI, per every HP of compressor motor.
Since your question is quite general as to the CFM output of the Ingersoll Rand HP355WP, in order to answer it, you would have also to indicate what the pressure level was of the compressed air you needed.
Also, I believe that this unit is around a 1999 Vintage, so why not visit www.ingersollrand.com, find the appropriate page, and email them for more information about your unit, since they are the source?
Make sure you indicate the required pressure.
Cheers,
Bill
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Air Tools and SCFM ratings
by Kenan
(Jericho, Vermont, USA)
I have Air Compressor from Porter Cable model CFNBNS rated at 2.6 SCFM @90PSI / 3.5SCFM @40PSI.
I would like to buy and use Task Force Spray Gun model TFK00100AV (lowes.com) that has "Average air requirement 5.7SCFM @40PSI".
My question is can I use this combination? If not why? Because requirement on paint spray is higher then the air compressor, is the AC going to run all the time and is it going to be short on air and under-performing?
Thank you,
Kenan
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Using a blower to achieve 15 psi
by Larry
(hamilton canada)
How many CFM blower would l need to achieve 15 psi at the discharge end of 50 feet of half inch black pipe?
Bill answers...
Hi Larry...
Fan sizing is a whole different kettle of fish from compressor sizing.
Please see these pages on this site for information about air flow and pressure drop.
Here's a list of blower manufacturers that might be better equipped to provide the information you need.
Regards,
Bill
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How many cfms can be pushed through a 2 inch pipe at 120psi
That's it. how many cfms can be pushed through a 2 inch pipe at 120psi?
Bill answers...
Hello visitor! Nice to hear from you, whoever you are.
It sounds like an easy question..how many CFM's can flow through a 2" pipe, except, that you overlooked one pretty important piece of information.
And that is, what's the length of the pipe?
Best thing you can do is read this page on pressure drop and then follow the links if you want the math.
Cheers,
Bill
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Where is it regulated that the PSI in the air lines has to be visible?
by Martin Lackie
In other words, is it a requirement that a tag or warning sign is required that shows the line pressure?
I have looked in OSHA and found only references to just line pressure.
I know some agency somewhere has regulated it to have warning signs posted on how much is carried in the line.
I did a walk through inspection and found several lines not marked. I told the shop person they needed to mark the PSI and they asked me where it is written. I figured that's a good question.
Any help would be appreciated.
Thanks
Martin
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PLEASE HELP more cfm
Hi
I have a small 6 gal. compresser that puts out 2.6 cfm @ 90 psi or 3.7 @ 40 psi. How can i increase the cfm at 90psi's . It is a pancake style with a max of 150 psi. It is great for nail guns and sprayers but i am trying to run a ratchet or saw.
Was a gift from the wife don't have the heart to tell her it is to small.Is there a way to add a extra tank?
Bill answers...
Howdy, and thanks for the question.
Yes, you can add a tank or tanks to your compressor to provide you with a larger reserve of pre-compressed air at 90 PSI or whatever pressure your compressor can take it up to.
If you have a number of tanks that are all pressurized at 150 PSI for example, and the regulator setting for the downstream air is 90 PSI, you'll get a longer supply of air at 90 PSI than if you just had one small tank.
More on adding an air tank here.
Unfortunately, the sad reality is that a 2HP compressor can't provide enough air at 90 PSI to run anything other than an intermittent air-using tool like a nail gun or staple gun.
A volume using air tool like a ratchet, saw or impact wrench will empty your air tanks very quickly, and then you will have to stop and wait while the little compressor tries to catch up. If you try to use it too much at one time, you run the risk of overheating it.
The little compressor is ideal for what it's designed to do. It's not the right one for a volume using air tool. Sorry.
Cheers,
Bill
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SCFM/PSI Relationship
by Joe
I'm shopping for an air compressor and see 40 psi and 90 psi as a common point of reference for SCFM.
Why is SCFM greater at 40 PSI?
Shouldn't more pressure facilitate the movement of more volume?
Bill answers...
Hi Joe:
Sigh! I wish the compressor manufacturers would recognize that air, coming out of a compressor discharge after being compressed, is no longer SCFM, but rather, CFM. That's my opinion, and I'll stick by it.
Here's information about what a SCFM is!
Now, to your question.
Your compressor has an electric motor, and the process of compressing air converts the electrical energy consumed by the motor into stored energy in the form of compressed air in the compressor receiver.
Since it's easier to compress air to 40 PSI than to 90 PSI, then the compressor, using the same amount of electrical energy, can produce more flow (in CFM, not SCFM) at the lower pressure than the high.
Energy cannot be created nor destroyed. It can only be changed from one type to another form of energy.
Since the electric compressor motor is already running at top speed, it's using all of the available energy it has, and since it's more work to compress air to 90 PSI than 40 PSI, you get less flow at the higher pressure.
If you were able to get more flow at 90 PSI than at 40 PSI, somehow the compressor would have to manufacture more energy than was available from the existing motor, and if you could make that happen, you'll be a very rich person!
Make sense? I hope so. Nice hearing from you.
Bill
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Bar vs scfm
by dale
(anderson sc usa)
6.9 bar = what SCFM
Bill answers...
Hey Dale, nice to hear from S.C.
Got a bit of a problem with your question, however.
Bar is a measure of pressure. One bar is 14.7 PSI, at sea level, and with another few specs thrown in.
So, 6.9 bar would be 6.9 x 14.7, or 101.43 PSI (pounds per square inch) give or take a couple of points, depending on where you are in the world.
SCFM is an acronym for Standard Cubic Feet per Minute. That's a measure of flow, not pressure.
That's why I was puzzled about your question.
Cheers,
Bill
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Converting Mpa to Psi
I just bought a air nailer gun and it is saying the compressed air pressure should be between 0.4-0.7Mpa's and I was just wondering what that would be in Psi.
Thank you for your help.
Howdy, and thanks for the question.
To convert MPa to PSI:
1 MPa = 145 PSI
To convert PSI to MPa:
1 PSI = 0.0069 MPa
Figures are approximate. If you wish greater accuracy, you need to add the decimal points, though for purposes of converting for air tool use, these conversions will do just fine.
My thanks to the Chapel Steel website: http://www.chapelsteel.com/psi-mpai.html for this information.
Cheers,
Bill
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How to calculate SCFM for my compressor.
by Tom
I have a 3hp, 20 gallon compressor.
What's the SCFM?
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Air flow (cfm) needed to maintain constant pressure (psi)
by Wolfgang
(Los Angeles, CA)
I need to figure out feasibility of designing a seal for large (about 15 ft diameter) piston being pushed within a 15-ft diameter steel pipe manufactured to standard industrial tolerances.
I.e. could a seal be designed to limit air leakage to, say, 1600 cfm - (i.e. capacity of a pretty large compressor)?
Another question is how long it would take to pressurize this large cylinder (Volume up to 30,000 cft).
Bill answers...
Hello Wofgang...
Regarding "could a seal be designed" for your application, I would expect yes. The place to get that information is a manufacturer of seals, and or a mechanical engineering firm.
As to "how long it would take to pressurize this large cylinder" you can find more information about air cylinder consumption right here.
In order to figure out the volume of air needed, you will need to know the air pressure required.
Cheers,
Bill
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What difference does the free air at a certain CFM make?
Is it better to have more free air at a certain CFM or to have maximum pressure?
Bill Answers....
Hello there. Thanks for the question, though I'm not exactly sure of the intent of it.
If you are asking about the capacity of a specific air compressor then two factors are important to most users.
The first is the amount of air, or the flow of compressed air that's available from that compressor, and the second important issue is - at what pressure is that flow available?
Most DIY applications for compressed air involve air tools. Each air tool will have a MOP (minimum operating pressure), and will require a certain flow of air at that MOP in order to work properly.
Compressors are usually rated by the number of CFM they produce at a specific pressure.
To confuse issues, some compressor manufacturers use the term SCFM to describe post-compressor air, but I contend that once air has gone through an air compressor, it's no longer "Standard" Cubic Feet per Minute, but rather, just CFM.
A small DIY type air compressor might boast a compressed air delivery rating of 4 CFM at 40 PSI. That same compressor might have a rating of 2.2 CFM @ 90 PSI, much less than the flow at the lower pressure.
The higher the pressure that's required the lower the flow that will be available from most air compressors.
To get back to your question, first of all, you don't have "free air" coming out the discharge port of your air compressor, you have so many CFM at so much air pressure of compressed air.
So, what's better? Neither. You have to determine based on your application if the flow and pressure from a particular air compressor is right for your application predicated on the compressed air demands of the tools and apparatus that you are planning to use.
Hope this helps.
Cheers...
Bill
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