Right Size for an Air Compressor

[Jimmy240Z]

Need some help. As you know I have been working on my floorpans, etc. I went out and bought an air saw and a cut off tool. I have a 2 HP 12 Gallon Air Compressor. Neither tool is cutting the metal. Not sure if it is a problem with the Air Compressor or what. I have tried to adjust the tools and that doesn't help the cutting. Someone said I need a larger air compressor. Can anyone give me their lessons learned on the right size for an air compressor?
Thanks,
Jimmy

[moonpup]

The tools you bought should list somewhere, either in the instructions or on the box, what the minimum amount of CFM's are required from your compressor in order to operate them. Compare that to your compressors CFM rating. Sounds like your compressor isn't generating enough.

[CoastGuardZ]

Jimmy,

I see you're in Charleston. What part? Charleston is home for me... I grew up in the Summerville/Goose Creek area and I am doing everything it takes to get back... hopefully next year.

I feel pretty confident in saying that your Compressor is too small. I have a Craftsman 1.5hp (that is the sustained hp the max developed is 3hp but that seems to be an arbitrary number) 15gal rated at 3.5 SCFM @ 90 psi... which is way too small for what I ask of it. I am currently in the market for a new compressor too, (Yes E, you can say I told you so). From what I can tell the minimum you should look for is a 6.0 SCFM @ 90psi. Also, it seems that all the larger "oil free" ones are quite LOUD. Mine is really annoying and so is my brother-in-laws... also a Craftsman, the 33 gal 2 hp (6hp?) which makes 6.4 SCFM @ 90. We have a BIG and I mean BIG compressor at work which is not as loud as my little "home-owner" one. I've decided that I'd like to get somewhere around 9 SCFM @ 90 psi / 30 + gallons and an oil lubed pump, which I guess means I'll be into one for around $400-$500 bucks. Good luck, and look for a PM from me.

Nate

[webdawg1]

I guess there's some truth in the old saying "Bigger is Better" LOL Get the biggest honking compressor you can get your hands on....You won't be sorry you got the bigger one...Well...maybe you will...when it comes time to move to another house you might have some second thoughts...LOL


webdawg1

[kurtwwalters]

I just got a 6hp 30gal Craftsman. I got a hold of a 120gal air tank from an industrial compressor that I want to use for sandblasting or anything else that will use a lot of air. I just need to get a few fittings for it. Anybody ever tried it? I got it for next to nothing so I thought I'd put it to use....

[CoastGuardZ]

I've heard of people doing but never myself. I would be worried about overworking the compressor motor to fill that big beast though. I don't know. I also have a feeling that, like mine, the hp number you have there is the "max developed" number and not the rating at wich the motor will be running at to fill that big 'ol tank, which is probably closer to 2 hp. So it may take a while and on top of that the motor may meet it's maker quite a bit sooner. Just a thought.

OTOH, it might be worth rigging up just to see how it goes. I would watch it the first few times to see how long it runs and how hot the motor gets.

Good Luck!

[jmortensen]

Adding the big tank should help because the motor won't be on as much if you're not running an air sander or something that you can run for an hour at a time. So if you're using say, an impact gun to break loose your lug nuts, with the small 15 gal or whatever size tank, the pressure in the tank might go down enough just while you're breaking them loose to cycle the compressor on. With the 120 gallon tank hooked up, no way.

I have basically been trying to break my 20 gallon, 5hp compressor. It is an oilless and it is so freakin loud I can't stand it. In an attempt to justify a nice 80 gallon oiled 220V compressor I've been not waiting for the compressor to catch up. I swear I've had that motor running for 2 hours with about 5 minutes of rest quite a few times now. It's gotten noticably looser sounding, especially when the air tank is empty, but it keeps going.

But yeah, the bigger is better idea is really the way to go when it comes to compressors.

[CoastGuardZ]

I have basically been trying to break my 20 gallon, 5hp compressor. It is an oilless and it is so freakin loud I can't stand it. In an attempt to justify a nice 80 gallon oiled 220V compressor I've been not waiting for the compressor to catch up. I swear I've had that motor running for 2 hours with about 5 minutes of rest quite a few times now. It's gotten noticably looser sounding, especially when the air tank is empty, but it keeps going.


ROFL

That's awesome! Good luck with that.

Yup, the noise is really begining to annoy the crap outta me too. At first I thought about trying to break it, but decided it would be better to make $50-$100 off of it to apply to the new one.

I too am looking at the 220v models... it really sounds like the way to go.

[DeesZ]

I am by no means an expert on compressors, but have learned a lot about them over the last several years. I decided to get a "larger" unit than the little guy I got several years before, and did some research before getting one. I'm glad that I did, because my normal impulse purchasing habits would not have served me well for this purchase. Here's a few things that I've learned... anyone with corrections or additions, please post them (again, I'm not an expert).

Proper compressor sizing will provide you with suitable performance and longer compressor life (because you will not 'overwork' the unit). Air compressors are rated by horsepower, pressure, and cubic feet per minute (CFM) of output at a given tank pressure. A good way to choose a compressor is to first decide which tools you are going to use with it (you have done that, but will you get bigger ones as time goes on?); the compressor should exceed the CFM requirement of the largest tool you will use by probably at least 1.5 times. If you plan to run more than one tool at a time off the same compressor, add the CFM's of the tools together before multiplying by 1.5.

Generally, tools like sanders, grinders, sandblasters, etc. need a continuous flow of air and will need larger, more powerful compressors to work properly.

Another issue to get a grip on is what is known as the "duty cycle". The duty cycle is usually expressed as a ratio - how much time the compressor can safely run within a given period of time. As an example, a common "duty cycle" for compressors is 50%, meaning that the compressor should not run more than 50% of one hour... During the "on" time, the motor is pressurizing the tank. During the "off" time, your tools are running on the air stored under pressure in the tank. If your tools are draining the pressure off too fast, the compressor must run at more than 50% of the time that you have it in use. (With the 50% duty cycle the maximum pumping time per hour would be 30 minutes.)

Horsepower ratings of electric motors can be measured several ways and the figures have been abused by manufacturers over the years, so they are not a reliable way to measure performance. The CFM and pressure ratings of an air compressor the absolute best measure of how a compressor will meet your needs.

You'll probably end up looking at a piston type compressor. There are several types of those to consider..... single-stage and two-stage. Single-stage compressors have one piston usually (sometimes two) that compresses air and delivers it to your storage tank. The single-stage system is normally found on light or medium-duty compressors with a maximum rating somewhere below 150 pounds psi. Single-stage compressors are adequate for many of our needs. Two-stage compressors have two pistons that compress air. The first piston compresses the air and pushes it through a check valve to the second piston. The second piston further compresses the air and delivers it to your storage tank. The two-stage system is usually found on better heavy-duty compressors with maximum ratings above 150 psi. Two-stage compressors are good choices for heavy use environments.

Then there is the decision to get an "oil-free" or "oil-lubricated" unit. Depending on what your needs are you may not have a choice. Oil free units require less maintenance, no oil changes, etc., but some people claim that they do make more noise and will not last as long. They are good for a lot of applications, and I know many happy users of that variety. I have very limited experience with oil-free units, and I have no complaints with them. "Oil-lubricated" units are most often found in more demanding environments. Some people claim that they are a bit quieter and that they last longer. Of course there is maintenance involved with oil changes. Personally I prefer the latter variety despite the maintenance (I have this 'thing' about parts rubbing each other without lubrication.... what can I say?) Any variety that you will get will be loud. I have never been around a quiet one, so consider 'placement' in your garage, and maybe some noise control.

Sticker price can be an eye popper for a nice unit, but don't skimp if you can possibly swing it. Consider what you may wish to use it for in the future, beyond your immediate needs. A good heavy-duty unit new will likely be between $900. ~ $1500. This is where patience can come in. I decided to look for a used well cared for unit. Found one (DeVilbiss brand) on eBay for $300.(plus a 150 mile drive) with about 50 hours of use - looks and performs like new, 80 gallon tank, oil-lubricated two-stage, and delivers 17.4 SCFM @ 100 psi & 16.9 SCFM @ 175 psi. I am very happy with the unit and it will meet any demands that I put upon it now and in the future. When I got home with it I asked my wife to help me get it out of the back of the truck... It was a bit big for me to do alone safely.... her only comment was "holy shit!"

[=Enigma=]

Thanks for the great info John. I've been meaning to do some research on this myself to replace the 6 gal 1.5hp unit I have. About all that's good for is filling tires, blowing out clogged lines, drying cleaned parts, and freaking out the neighbor's cat when she's taking a dump in my garden. LOL

[Jimmy240Z]

I found two compressors at Lowes today, both are by Kobalt. Both are 220 volt and they are oil lubricated. The larger is 7HP 60Gallon 13.3 SCFM@90 PSI and the price is $499.00. The smaller is 6HP(?) 45Gallon 11.? SCFM@90PSI and the price is $399.00. I'm thinking that I am goping to go for the bigger. The extra $100.00 is only a question at the time of purchase and by the time I start using it for all the body work etc. I am going to be glad for the extra capacity.
Jimmy

[geezer]

Great info. John. I would say Jimmy, you get what you pay for when buying a new unit. There are many different ways to decribe a compressor and when they are marketed they tend to get creative sometimes, clouding the decision. Ultimately the SCFM rating should give the best indication of the units capability. HP claims don't always hold true either. A few things that come to mind are, the intended use, space constraints and noise levels. I have two. One is a portable and one is a larger industrial (took 4 guys to get off the truck). I don't know the specs. offhand but the smaller is rated at 2HP and runs on both 220V or 110V. It will run an air cutoff wheel for about a minute, but because of the small 20 gal. tank and small pump is not practical. The larger unit I bought back in 1984. It is a true 5HP and has an 80 gal. tank. It will run the same cutoff wheel all day and never leave me waiting for enough air. It will power my sandblaster at about a 50% duty cycle. It still isn't big enough for me though and I borrow a diesel unit for larger sand/bead blasting projects. The one you are considering sounds to be a good choice and the price seems reasonable too.
I built an enclosure for mine, for several reasons and it has served me well. It is located out of the garage and thus doesn't take up valuable space. The enclosure is constructed using a staggered stud arrangement and insulated with sound proofing materials. The compressor can barely be heard from in the garage. It is supplied with filtered air from a stack. It stays clean also. The only thing in the garage is the automatic oiler running from one line, the regulator, the moisture bottles, a recoil spool for the hose (all wall mounted) and an overhead swivel airline. A compressor this size will need a starter box also. They can be on the pricey side too. Just a few things to consider. Good Luck

[beandip]

I have been using two different compressors during my restore/redo of my Z. My Son in law has a portable, Sears compressor that is rated at 9+ CFM at 90 psi , I believe, Could be bigger than that. I think he paid about $200.00 on sale. My own unit is the kind used by contractor's for nailers, the type with two small tanks . What I am getting at is. What are your intentions in the use of the compressor and your air tools. I am not a professional mechanic or body man. The larger unit I used , I found ample to run die grinders and a DA sander and what ever I wanted. Occasionally I did need to stop and let the unit recover with the more '' air hungry'' tools. It was just fine for painting my Z as well. If I were going to be doing this type of work on a daily basis I would definitely buy a commercial compressor. My little unit will run a impact gun, flat ratchet, and die grinder fine for occasional use now that my Z is done. As if they are ever done. LOL When I was in construction I always bought the best tools I could . And was never sorry. Now I have no need for such quality , because they are not used on a daily basis. What DeesZ has posted is right on the money on choosing the right unit. You just need to decide what your intentions are and how much you will be needing the full capacity in the future. I am not planning on a future project car, Gary:rambo:

[Go240Zags]

Anyone have any experience with this Harbor Freight compressor - would this be adequate for most jobs. My mind is starting to swim over all the numbers. It's not rated as high as the one Beandip describes, but would this work for most applications? http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94667

[Walter Moore]

I bought a similar compressor at Big Lots a few years back. Mine appears to be the same motor and pump, but with a smaller, horizontal tank. The specifications for mine are very similar to that unit as well.

I paid around $99, on clearance. (Clearance... at Big Lots... LOL )

Within a year the pressure switch broke. The cheap plastic body just came completely apart. When that happened the motor would never shut off. It ran non-stop. (There is a small emergency pressure relief valve to keep the tank from exploding.)

But the copper tubing that connects the pump to the unloader valve on the tank split at the same time that the pressure switch broke. ( I suspect that one failure caused the other, but do not know which one happened first.) I have heard that the pipe is copper to act as a pneumatic fuse of sorts, but am not sure if that is true.

Anyway, to repair it I had to buy a new pressure switch, and some 3/8 black pipe. (I don't have access to the copper tubing.) The pressure switch was around $50 (Granger's) and the black pipe was more than $20. (For some reason 3/8 pipe is hard to find.

By the time I got it running again I had put an additional $70 into my $99 compressor. All that and I still don't have the volume to do much more than inflate tires, and run my "air vac" while bleeding brakes.

I guess what I am saying is that going cheap rarely pays in the end.

[CoastGuardZ]

Anyone have any experience with this Harbor Freight compressor - would this be adequate for most jobs. My mind is starting to swim over all the numbers. It's not rated as high as the one Beandip describes, but would this work for most applications? http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94667

That's not much more output than what I have now, which is nowhere near adequate. It's my opinion that the minimum to look at is 9+ SCFM @ 90psi, and looks like this number is more efficiently met with a 220v (208v-240v) motor. You should figure out what the most air hogging tool you have or plan to use is and go 1.5 times more than that. For example, my angle die grinder requires around 6 SCFM, so 9 SCFM is a good place to start. A very important thing to look at is Duty Cycle... the closer to 100% the better.

Here is a Harbor Freight one that I am considering...
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92504

Nate

[kurtwwalters]

One thing I had to consider was if buying a 220V compressor, I would have had to get an electrician out to the house to wire it. I don't know about you guys, but I don't have 220 in my garage... though next time I have one come out to fix some other problems I'll have him wire my old oven so I can do powdercoating...

[CoastGuardZ]

It's not hard... you can do it. Many people are afraid of it for some reason, but it is quite easy and safe if just take your time and pay attention to what you are doing. Lowe's will even show you how...

http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/220outlet.html

[ncz]

Hey guys, back up after a time off. I hear you on the compressor quandry, been there. Started with the Craftsman 5hp 30gal tank(6scfm I think). Won't run a cutoff tool or strait line or da sander. Also won't run the air sabre saw nor a small abrasive blaster without blowing up. Also if you want to paint with an HVLP gun, you need higher CFM at low pressure. Go to Home Depot, they will have a two stage compressor that is about 3-5hp with a 60 gal tank, that will get you up to about 12 scfm/10.5 scfm at 40/90. You can get this model for $799 in my area. They have a bigger one on display(80 gal, 7hp) but it is $1699. The smaller one will work for most of us hacks. Also dittos on the noise. The old Craftsman would bring everyone out to the garage to yell at me about the noise, funny to see my daughter holding her ears and telling me to be quiet she can't hear Sponge BobLOL . Thats the best deal I found for the money. PS, if you can, get the best air dryer you can afford, will save your tools and help greatly if you want to paint. Ok, someone help get my welding back on track!!!

[geezer]

I just checked mine out to see what's up. Either this is one of those products that has come down in price over the years, or maybe I paid too much. Mine is an Ingersoll-Rand 5HP 230V single phase, double reciprocating pump with a centrifugal unloader. 80 gal. tank. It has a baseline rating of 23.1 CFM @ 100 psi. Weight 630 lbs. The total price with sales tax came to $1551.35 CDN. That didn't include the starter switch that I bought separately, but they tossed in an airfile. Looking back I would say it was worth the money. It is now 23 years old, is used quite frequently and has never had new rings or bearings. The only thing I've done is change the oil & filters yearly and clean the valves and change the belts, every few years. The thing I find interesting about this topic is the seemingly out of whack CFM ratings.

[Go240Zags]

One thing I had to consider was if buying a 220V compressor, I would have had to get an electrician out to the house to wire it. I don't know about you guys, but I don't have 220 in my garage... though next time I have one come out to fix some other problems I'll have him wire my old oven so I can do powdercoating...

It's not hard... you can do it. Many people are afraid of it for some reason, but it is quite easy and safe if just take your time and pay attention to what you are doing. Lowe's will even show you how...

http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/220outlet.html


The 220 thing has always been a sticking point for me. My old electrical box doesn't have any room for any new breakers. When I needed a new 220V for my submersible well pump the electrician had to get two of these special breakers where twin switched breakers fit in a slot where only one would go normally. Then one from each of these new double breakers (the two switches adjacent to each other, in the middle) was used for the 220V and the two remaining switches (on the outside) were left at 110. I don't know if my description makes sense, but it worked. I'd have to go the same route for my garage, but might be able to get away with tapping into the well pump line, as it runs right by the garage. But I'll leave these things to the electrician. I get nervous installing a new light fixture.

[CoastGuardZ]

I can see how no room in the breaker box might pose a small issue... LOL

Well, I went to HF today and checked out their compressors and I think I found the one I'm going to get, it's only $400...
http://www.harborfreightusa.com/usa/itemdisplay/displayItem.do?itemid=3848&CategoryName=AIR%20COMPRESSORS&SubCategoryName=AIR%20COMPRESSORS

I also found that HF has two websites, their catalog site www.harborfreight.com and their retail store site www.harborfreightusa.com

I did a little research on this compressor (U.S. General US660V) and found that the compressor motor itself is the same one used (made) by the company producing Bel-Aire compressors. Not really sure if that's a good or bad thing but I found it out none-the-less.

Do any of the air compressor guru's see any issues with this model? Will I run into any issues with it being a 135psi model?

[DeesZ]

Geezer.... Others may not agree or see the issue the same way, but I think you made a good buy on that compressor. It was a chunk of change back then, but look at what you got.... how many years of excellent service you have gotten?.... over twenty so far.... and it's likely going to work well for the next generation of your family. Ingersoll-Rand made a fine compressor back then, and there wasn't much competition from the Japanese and especially Chinese import goods. You "bought well, and bought once", and there is a true economy to that approach. Had you started small or medium and worked up the ladder to what you now have, you would have paid perhaps twice that amount in total (considering you would have taken a beating on 2 or 3 other compressors by the time you got your last one). And 23.1 CFM @ 100 psi is nothing to sneeze at, even today. Most compressors are delivering a fraction of that. Your needs have been well met, and you have a considerable volume of excess capacity. The out of whack CFM ratings you reference do seem that way and I think it is because there are so many units being offered at discount prices - with the "I wish I knew that when I bought this" sacrifice of SCFMs. As I posted earlier, my advice to someone looking to buy, is to look at the SCFM need you will have, multiply it by 1.5 or 2, and buy accordingly.
For those of you considering a purchase, don't be fooled by a big tank. They are an important part of the "delivery" equation, but there is a lot more to it than just the tank. And "delivery" is exactly what you are looking for. You want a machine that will "deliver" enough air to truly satisfy your needs, so focus on the SCFM, and make a purchase that solves your needs. And if you are thinking about growing into a larger one, you will likely spend less in the long run by meeting your needs with your first (or next) purchase. I truly realize what happens when you go to buy one. Been there. Once you figure what you really need now and in the future, and get by the analysis paralysis (I had a bad case of that) the sticker shock sets in. For many of us the range faces $1000.+, and that's way too much to justify. The wife and kid will need clothes too, and It's nice to feed then every now and again. I found myself compromising to make my needs fit my budget. I resolved that I would buy on the lower end so I could at least get one. Then I ran in to one being sold by a friend - nice big unit in good shape! Bigger than what I needed, and half the price of a new one... in other words "excess capacity for the price that I could afford". Well, I guess I was too excited, or something. The guy decided to hook it back up and keep it. So, knowing that I can get what I need affordably If I look around and wait for a good used one, that's what I did. Glad I did, too, because I got one that should last a lifetime and satisfy all future needs for less than the first one I almost bought. There are thousands of good units out there not being used in somebody's garage that will exceed your needs for less than the cost for the new one that doesn't really do the job. Unless you must buy a "new" one for some reason, look around for a while and see what comes up. It tool me 6 months or so, but I ended up spending one-third of what I was going to spend, and I got twice the SCFM than I was going to "settle" for before. The wife and son were able to eat, and I was happy.... a rare combination around my place. They want crab legs - I want Castrol.....
A good compressor can easily become the heart of your garage. Purchase wisely, or purchase often. I have nothing against used - but very well cared for - equipment. I will never buy another new vehicle again, either for similar reasons. I guess it boils down to the issue of "value": Getting something that meets your needs & pleases you, at a reasonable cost.

[geezer]

A couple of points I would like to make. It is pretty hard for the average hobbiest to lay out the amount of coin it takes to buy a compressor which suits their wants. What ever you buy, there is a bigger, better one beckoning you. Practicality and price, becomes the issue and will usually determine what you buy. The only reason I bought the one I did was, I needed it. At the time my brother and I were operating a small shop specializing in custom body & paint. It was just a sideline for me, but was his livelihood. After he moved on to bigger and better things, we divvied up the equipment and the compressor stayed with me. Otherwise I would still only have the 2 HP Cambell Hausefield (25 yrs old and going strong).
If your plans are just restoring one car, it is hard to justify buying anything other then one like CoastGuardZ is considering.
John brings up a great point. Buying a good quality used one is the smart way to go. Especially if you know the history of it. If I had to buy another that’s the way I would go. I just want to make clear, I am no expert on this subject, and the choices out there today are just as mystifying to me.

[CoastGuardZ]

I found two compressors at Lowes today, both are by Kobalt. Both are 220 volt and they are oil lubricated. The larger is 7HP 60Gallon 13.3 SCFM@90 PSI and the price is $499.00. The smaller is 6HP(?) 45Gallon 11.? SCFM@90PSI and the price is $399.00. I'm thinking that I am goping to go for the bigger. The extra $100.00 is only a question at the time of purchase and by the time I start using it for all the body work etc. I am going to be glad for the extra capacity.
Jimmy

Hey Jimmy, have you commited yet? I went to Lowes today and looked at both. I think I have made up my mind too. I want the "bigger" of the two, it has a 100% duty cycle and also the recomendations on the sticker list sandblasters, die grinders and DA's as continuous use - I'm sure this is in thanks to the 100% duty cycle. Looks like a very good unit. Add a pressure regulator and line dryer and you'll be in buisness.

After a little research it looks like the Kobalt, U.S. General, DeVilbiss and Bel-Aire have a lot in common. They tend to use either the Century motor or the A.O. Smith motor. Tanks are similar, if not identical too. Some of the other (not exactly insugnificant) parts may be the only difference between the $400 U.S. General and the $1000+++ units from DeV & Bel Aire.

The Kobalt has a 3 year warranty and the support of a very large chain of stores, so I think I've made up my mind.

There are a lot of compressors out there and a lot of good info on theory and how to buy them... but I'm having to settle for Price + Output = Bang for the buck $. I think a little preventative maintenance ( regular oil changes, air filters and a water remover) will go a long way.

Nate

[beandip]

[QUOTE=geezer;218169]A couple of points I would like to make. It is pretty hard for the average hobbiest to lay out the amount of coin it takes to buy a compressor which suits their wants. What ever you buy, there is a bigger, better one beckoning you. Practicality and price, becomes the issue and will usually determine what you buy. The only reason I bought the one I did was, I needed it. At the time my brother and I were operating a small shop specializing in custom body & paint.
I agree with geezer. If you are only going to restore a Z and not in business. Unless money is no object , keep in mind how long a particular job is going to take. I could run away from the Son in law's unit if I ran the flat board sander continuously , or if I did the same with a DA sander. If I paused for 30 seconds or so the pump caught up and I continued on . Painting is an completely different issue . To paint it is a must not to stop like that and we didn't have any such problem . If I planned on doing body/paint work for a living or restoring several cars this is another issue. The Harbor Fright compressor for $400. is Plenty for a restoration or three , and then some. The other day I used my little compressor and cut some springs on my Z . Because of the small tanks and the hungry cutting tool , I had to stop three times for each coil to do the job. I wont be doing this again and I was not in a great hurry so it worked fine. It is a compressor for running nailers the kind carpenters use. Like Geezer, I bought it when I was using it for a different application and it had to be portable also. Now this is all that I need for my use , working on my cars. I was going to sell it and buy a larger one , but I don't see the point now. Gary