How big does my air compressor need to be?

[Sanderguy777]

I am slightly in the market to find an air compressor. I have a 6g one that technically works, but even has trouble with a framing nailer if I do too many nails in a row.

I want to be able to run a die grinder, a sander, and a paint sprayer (not at once, obviously).

What i need to know is how big and how expensive do I need to go to do that?

Can I get a used tank and then add a HF compressor motor somehow? I would like it to be quiet, but it is not the end all goal. If I have to get new, then how much would I have to spend to get a compressor that will last? I rarely use it but I am hoping to have more projects and use for it soon.

Budget would be as little as possible. I am just looking at what I would need, then making a plan from there. I assume I would need at least $500 for anything, even used (for repairs), but less is better.

 

[Firebrick43]

You are going to assess you needs more closely before an answer can be given

What kind of painting are you wanting to die and how large of area/gun and HVLP/siphon?

Same with die grinder. They come in multiple sizes and cheap ones use a lot more air that more expensive ones.

Unless you are planning on painting whole cars many can get away with a 21 gallon model, quiet versions exist.

You can tie two compressors together for the capacity if needed as well, many YouTube videos showing that if you need a little more umpff later on.

The other school of thought is to go big and get a 5 hp model which should cover most DIY even if you decide to get air hungry tools or a sand blasting cabinet in the future

Be aware that box store compressor manufactures generally lie about the HP on their compressors. Look at CFM @ psi numbers not HP when comparing.

While there are quiet models out there they generally are more expensive if the have any significant output capacity.

 

[GeoBruin]

This topic comes up quite frequently, and there are usually a few camps people fall into, but there is generally consensus that for tools like a die grinder, you need a pretty big compressor to use it a lot. Here's a recent write up I did in response to a similar thread the addresses this question:

Post in thread 'Need some air compressor advice'

Need some air compressor advice

I’m looking to buy a different air compressor; I have an older 25gal horizontal craftsman. I want to get a 30gal vertical. Any recommendations would be great, (and the ones to avoid). I have a limited budget so the less expensive the better. Thanks.

www.garagejournal.com

Also, here's a link to a series of tests I did showing the true Instantaneous air consumption of a variety of air tools. The numbers may surprise you.

 

[Rinspeed]

Budget would be as little as possible. I am just looking at what I would need, then making a plan from there. I assume I would need at least $500 for anything, even used (for repairs), but less is better.

If you have a Tractor Supply fairly local they usually have pretty good compressor sales on black Friday. I know they have IR and Dewalt, not sure what others. I've had a Dewalt 60 gal for four years and been pretty happy with it. I looked for two or three months for a decent used 80 gal but couldn't find anything close enough for a decent price.

 

[niget2002]

You can Frankenstein a compressor, but typically it ends up cheaper to buy one.

I built mine, but it's because I was given a tank and pump for free.

Die grinders and Sanders will use more air than a hvlp spray gun.

 

[Steve_P]

As said, a million threads on this. Realistically you need 240V, 15A minimum circuit, and at least a 10 CFM at 90PSI compressor to do what you want.

Edit- if you plan to paint a car in one session with a full size HVLP gun, you will need more compressor than above.

 

[Citation]

Something like that

 

[Sanderguy777]

You are going to assess you needs more closely before an answer can be given

What kind of painting are you wanting to die and how large of area/gun and HVLP/siphon?

Same with die grinder. They come in multiple sizes and cheap ones use a lot more air that more expensive ones.

Unless you are planning on painting whole cars many can get away with a 21 gallon model, quiet versions exist.

You can tie two compressors together for the capacity if needed as well, many YouTube videos showing that if you need a little more umpff later on.

The other school of thought is to go big and get a 5 hp model which should cover most DIY even if you decide to get air hungry tools or a sand blasting cabinet in the future

Be aware that box store compressor manufactures generally lie about the HP on their compressors. Look at CFM @ psi numbers not HP when comparing.

While there are quiet models out there they generally are more expensive if the have any significant output capacity.

Yeah, by quiet, I meant more along the lines of oiled, and from what I've heard, bigger ones tend to be quieter since they don't need so much movement to get the same volume.

I have a chief die grinder, so pretty cheap, but not trash level. HVLP wise, I would MAYBE do a tablesaw cabinet, so maybe the same area as a quarter panel but a more complex shape?

Let's say I wanted to do sand blasting some day, would a 30g have any chance of keeping up?
I know the specs are super skewed, which is why I was wondering what brands and sizes tend to be better about it. Usually industrial tools are accurate, so if you said an 80g or something, then I'd know pretty well that it would work.

This topic comes up quite frequently, and there are usually a few camps people fall into, but there is generally consensus that for tools like a die grinder, you need a pretty big compressor to use it a lot. Here's a recent write up I did in response to a similar thread the addresses this question:

Post in thread 'Need some air compressor advice'

Need some air compressor advice

I’m looking to buy a different air compressor; I have an older 25gal horizontal craftsman. I want to get a 30gal vertical. Any recommendations would be great, (and the ones to avoid). I have a limited budget so the less expensive the better. Thanks.

www.garagejournal.com

Also, here's a link to a series of tests I did showing the true Instantaneous air consumption of a variety of air tools. The numbers may surprise you.

I'll take a look. I glanced at a couple posts, but figured I'd ask about my specific needs. I will take a look.

My die grinder does about 1 minute of work before it has to huff and puff to get back to anything like pressure. But it has a 100% duty cycle, so it SHOULD be ok.

Can I add a tank, or 2ould that not help and just add to the time the pump runs without helping much?

 

[Sanderguy777]

As said, a million threads on this. Realistically you need 240V, 15A minimum circuit, and at least a 10 CFM at 90PSI compressor to do what you want.

Oof. The circuit is the easy part of that.

The 10CFM doesn't even exist in the "top of the line" stuff at HD that I have seen. Much less at 90 PSI LOL (I might be wrong, but seems like 8 or 9 at 40 was doable.)

 

[Sanderguy777]

Something like that

LOL. Yeah, I'd be happy with that volume, but i feel like the air would leak a bit...

You can Frankenstein a compressor, but typically it ends up cheaper to buy one.

I built mine, but it's because I was given a tank and pump for free.

Die grinders and Sanders will use more air than a hvlp spray gun.

Really? I guess they need more power than just volume, but wow.

 

[Citation]

Really, if you get anything 240V, 15A your are likely to be fine. I would look used in your area to see if any deals can be had.

I fine my zip wheel to be just ok with my 26g, belt drive 120V compressor. I think it's around 5.5cfm @90 psi. Overkill for most of what I do but marginal for air drills and grinders. Basically, if you can't do 240V the next worst option might be to try pairing two compressors together. You will need separate 120V circuits to pull that off. It's not too hard but does have considerations like making sure both pumps don't turn on at the same time and the safety blow off valves are compatible (you didn't want one compressor to over pressurize the other).

 

[niget2002]

LOL. Yeah, I'd be happy with that volume, but i feel like the air would leak a bit...



Really? I guess they need more power than just volume, but wow.

The HVLP is usually pulled down to < 25psi while spraying so while it's high volume, it's a low pressure. My pump puts out 90+ psi when running, so it can usually build up pressure in the tank even while the sprayer is spraying.

The die grinder and sander usually run at a higher PSI and similar volume while running, so they empty the tank faster and the pump has to run longer to refill the tank.

Or at least this has been my experience with all of those tools.

 

[Firebrick43]

Yeah, by quiet, I meant more along the lines of oiled, and from what I've heard, bigger ones tend to be quieter since they don't need so much movement to get the same volume.

So some large 5hp compressors spin a smaller pump faster to give the same cfm at a lower price than a quieter larger displacement pump turning slower. And there are some small cast iron recip such as the makita MAC700 that are pretty quiet as far as small recips go and then there are the California AIr tools silent compressors and clones that are really quiet and I believe they make those up to 30 gallons?

I have a chief die grinder, so pretty cheap, but not trash level. HVLP wise, I would MAYBE do a tablesaw cabinet, so maybe the same area as a quarter panel but a more complex shape?

A 5-6 cfm compressor should be able to do that without to much fuss.

Let's say I wanted to do sand blasting some day, would a 30g have any chance of keeping up?

No. Sand blasters are hungry. Small cabinets with standard nozzles are 15 cfm machines. Obviously you could use a small nozzle but it’s going to be seriously slow if you are only pushing 5 cfm

I know the specs are super skewed, which is why I was wondering what brands and sizes tend to be better about it. Usually industrial tools are accurate, so if you said an 80g or something, then I'd know pretty well that it

In your case I would probably buy a California air tools 2hp 20 gallon compressor for the main quiet use one and pair it with a cheap recip compressor of the same cfm for light sand blasting or serious air tools silent compressors use and in the less common events the extra noise could be tolerated for brief times. Of course as citation mentioned you would need to separate circuits to plug into for.

 

[T VETTE]

I had small compressors most of my life and really limited my work. A few years ago I finally said enough and went to Tractor supply on a black Friday deal and got an Ingersoll Rand 5hp. I can now run anything from my **** Blaster to any orbital sander or paint gun with no issue. Now that I think about it we are on year 5 and no issue with the IR.

Wish I had not waited so long in life to do this. Yes it is a bit loud but I don't work right next to it and also a pair of ear plugs take care of the problem, and besides the grinder or blaster is noisy enough to require ear plugs so it is a mute point.

 

[Citation]

... then there are the California AIr tools silent compressors and clones that are really quiet ...

To be fair to the clones, CAT was just one of the early ones to market those quiet models in the US. Some of their earlier stuff was the same loud Chinese compressors sold at the parts stores. The first of the quiet compressors I used was a GMC Syclone (not the truck). I didn't know who was first to market

 

[theoldwizard1]

Things like die grinders, cut wheels, sanders and sand blaster take lots of air !

8CFM - 10CFM @ 90 psi

 

[MoonRise]

Oh boy, another air compressor question.

5 cfm is NOT going to run a die grinder continuously or for long.

And you say, "But the manufacturer says it only uses 4 cfm. Why is a 5 cfm air compressor not enough to run a 4 cfm air tool?"

Because air tools are 'rated' on a 15 second use in a one minute period.

So that 4 cfm rated die grinder is actually using air at a rate of about 20 cfm. These are example numbers but close to general real world numbers.

A bigger air tank let's you run your air tool a little longer before the compressor pump starts up and tries to refill the tank, but takes longer to refill (among other trade offs).

The rating on the compressor pump is what matters most for sustained air tool use. But check the motor and pump duty cycle, as a lot of units are NOT rated for continuous usage.

A 120v air compressor is only going to give you about 5 cfm or so, as there is only so much electrical power available from the outlet.

So realistically, if you want to run an air die grinder or air sander or a full-sized spray gun (nit an air brush or a small detail gun), you are looking at getting a 240v machine.

Those typically start at 60 gallon and '3 hp' which usually can provide about 10-11cfm @90psi. But as I said, check the duty cycle. And that size unit will still not have enough air capacity to run a die grinder for very long.

$500 is not going to get you even that size unit nowadays IMHO, unless you luck into a deal.

About 8 years ago Tractor Supply had a Black Friday deal on a 60 gallon 10 cfm or so Dewalt air compressor for under $500 IIRC. Last I saw, that unit or similar is now over $800 or so. And the old sale was maybe $100 or so off, not $300+ off.

This is all for reciprocating air compressors, scroll compressors are usually quieter and a better duty cycle rating but cost much more. Eastwood has (or had) a small scroll air compressor, but that was about $2k last checked.

 

[Torque&Recoil]

I know the OP mentioned low cost, but I'm going to share my personal experience.

1. My first compressor was a 3 hp Craftsman. Clearly inadequate and I felt like I wasted my money. Sold it. Lost hundreds.
2. Got a 5 hp Coleman. Better, but couldn't really keep up. Fell under the category of "exaggerated horsepower rating". Wasted more hundred dollar bills.
3. Got a 5 hp 60 gallon Ingersoll Rand from TSC. Now we're talking. 18 SCFM at 90 psi could handle just about anything, but almost not enough for sandblasting, Yes, really. Even with 18 SCFM it runs continuously and the pressure drops when I am blasting. I have run that one for about 15 years without a single glitch. Well, I did have to tighten the belt once.
4. Two months ago - got a two stage IR from TSC with 80 gallon tank. What I should have bought in the first place.

When I was first getting started, a friend tried to warn me, but I didn't listen. He said, "Don't buy anything until you can afford a big one". I wasted about a thousand dollars on the first two compressors, trying to make do, when I could have just bought a good one up front and saved money in the long run.

My honest advice - Get at least a 5 hp 60 gallon compressor. Where I live, the best deals are Tractor Supply, in either IR or Dewalt. I have been very happy with IR, but others prefer Dewalt. Stuff goes on sale regularly. Just... do... it. If you can't afford it - wait until you can.

 

[OccupantRJ]

I do a LOT of blast cabinet usage. Around 20 cfm is what is needed at a minimum to progress properly and not be frustrated. The air jet in a decent suction type blast gun can be sized to match the output of the compressor. My compressor runs non stop during blasting, then shuts off 45 seconds after stopping the blasting.
In blasting some air is good, more is better, and too much is just enough.

 

[MoonRise]

I checked Eastwood. The scroll compressor delivers 12.7 cfm @ 90psi. The price is now $3150, ouch. But it is quiet, less than 70 dB.

As mentioned, more air is better.

 

[impactims]

I am slightly in the market to find an air compressor. I have a 6g one that technically works, but even has trouble with a framing nailer if I do too many nails in a row.

I want to be able to run a die grinder, a sander, and a paint sprayer (not at once, obviously).

What i need to know is how big and how expensive do I need to go to do that?

Can I get a used tank and then add a HF compressor motor somehow? I would like it to be quiet, but it is not the end all goal. If I have to get new, then how much would I have to spend to get a compressor that will last? I rarely use it but I am hoping to have more projects and use for it soon.

Budget would be as little as possible. I am just looking at what I would need, then making a plan from there. I assume I would need at least $500 for anything, even used (for repairs), but less is better.

What I use. Highly recommended.

Quiet, can run all day every day without a problem, lots of air for whatever you may need.

 

[Sanderguy777]

Really, if you get anything 240V, 15A your are likely to be fine. I would look used in your area to see if any deals can be had.

I fine my zip wheel to be just ok with my 26g, belt drive 120V compressor. I think it's around 5.5cfm @90 psi. Overkill for most of what I do but marginal for air drills and grinders. Basically, if you can't do 240V the next worst option might be to try pairing two compressors together. You will need separate 120V circuits to pull that off. It's not too hard but does have considerations like making sure both pumps don't turn on at the same time and the safety blow off valves are compatible (you didn't want one compressor to over pressurize the other).

Yeah, I can definitely do 240v.

As for the 2 compressor system, all the safety would need is for both compressors to have the same rating, right? Like 125psi.

 

[Sanderguy777]

So some large 5hp compressors spin a smaller pump faster to give the same cfm at a lower price than a quieter larger displacement pump turning slower. And there are some small cast iron recip such as the makita MAC700 that are pretty quiet as far as small recips go and then there are the California AIr tools silent compressors and clones that are really quiet and I believe they make those up to 30 gallons?

A 5-6 cfm compressor should be able to do that without to much fuss.

No. Sand blasters are hungry. Small cabinets with standard nozzles are 15 cfm machines. Obviously you could use a small nozzle but it’s going to be seriously slow if you are only pushing 5 cfm

In your case I would probably buy a California air tools 2hp 20 gallon compressor for the main quiet use one and pair it with a cheap recip compressor of the same cfm for light sand blasting or serious air tools silent compressors use and in the less common events the extra noise could be tolerated for brief times. Of course as citation mentioned you would need to separate circuits to plug into for.

I don't need quiet that bad. For the price, I could get an oiled pump that would probably be fine. Worst case, I can add a lean-to for the compressor on the outside of the garage.

 

[Sanderguy777]

Oh boy, another air compressor question.

5 cfm is NOT going to run a die grinder continuously or for long.

And you say, "But the manufacturer says it only uses 4 cfm. Why is a 5 cfm air compressor not enough to run a 4 cfm air tool?"

Because air tools are 'rated' on a 15 second use in a one minute period.

So that 4 cfm rated die grinder is actually using air at a rate of about 20 cfm. These are example numbers but close to general real world numbers.

A bigger air tank let's you run your air tool a little longer before the compressor pump starts up and tries to refill the tank, but takes longer to refill (among other trade offs).

The rating on the compressor pump is what matters most for sustained air tool use. But check the motor and pump duty cycle, as a lot of units are NOT rated for continuous usage.

A 120v air compressor is only going to give you about 5 cfm or so, as there is only so much electrical power available from the outlet.

So realistically, if you want to run an air die grinder or air sander or a full-sized spray gun (nit an air brush or a small detail gun), you are looking at getting a 240v machine.

Those typically start at 60 gallon and '3 hp' which usually can provide about 10-11cfm @90psi. But as I said, check the duty cycle. And that size unit will still not have enough air capacity to run a die grinder for very long.

$500 is not going to get you even that size unit nowadays IMHO, unless you luck into a deal.

About 8 years ago Tractor Supply had a Black Friday deal on a 60 gallon 10 cfm or so Dewalt air compressor for under $500 IIRC. Last I saw, that unit or similar is now over $800 or so. And the old sale was maybe $100 or so off, not $300+ off.

This is all for reciprocating air compressors, scroll compressors are usually quieter and a better duty cycle rating but cost much more. Eastwood has (or had) a small scroll air compressor, but that was about $2k last checked.

Yeah, a scroll one would be ideal, but not worth it for my usage.

I want quiet, but I don't want to pay for it. The main thing was if someone recommended a HF oil-less or something LOL. Pretty much anything I use the thing for (and all the high volume ones) is going to need ear protection.

The 60g is a good start, as is the 240v. I have plans for a 240v circuit for the tablesaw anyway, so that just means I might add another box down the line.

 

[Sanderguy777]

I know the OP mentioned low cost, but I'm going to share my personal experience.

1. My first compressor was a 3 hp Craftsman. Clearly inadequate and I felt like I wasted my money. Sold it. Lost hundreds.
2. Got a 5 hp Coleman. Better, but couldn't really keep up. Fell under the category of "exaggerated horsepower rating". Wasted more hundred dollar bills.
3. Got a 5 hp 60 gallon Ingersoll Rand from TSC. Now we're talking. 18 SCFM at 90 psi could handle just about anything, but almost not enough for sandblasting, Yes, really. Even with 18 SCFM it runs continuously and the pressure drops when I am blasting. I have run that one for about 15 years without a single glitch. Well, I did have to tighten the belt once.
4. Two months ago - got a two stage IR from TSC with 80 gallon tank. What I should have bought in the first place.

When I was first getting started, a friend tried to warn me, but I didn't listen. He said, "Don't buy anything until you can afford a big one". I wasted about a thousand dollars on the first two compressors, trying to make do, when I could have just bought a good one up front and saved money in the long run.

My honest advice - Get at least a 5 hp 60 gallon compressor. Where I live, the best deals are Tractor Supply, in either IR or Dewalt. I have been very happy with IR, but others prefer Dewalt. Stuff goes on sale regularly. Just... do... it. If you can't afford it - wait until you can.

Yeah, that is what I'm thinking. Only other way is if I got a used one cheap, but then I might just be bringing a time bomb into the shop. literally. I really don't get why they don't make tanks from aluminum ...

 

[Sanderguy777]

What I use. Highly recommended.

Quiet, can run all day every day without a problem, lots of air for whatever you may need.

15hp!? I said cheap, and all you all latch onto is quiet. I can buy a lot of ear plugs for the price difference LOL

That thing looks awesome and sounds (quietly) like a great machine, but I don't have enough amps in the whole shop to get even near 15hp, much less the money for that beast. I wish I did, though!

 

[jabberwoki]

Bout this big should do it.

 

[impactims]

15hp!? I said cheap, and all you all latch onto is quiet. I can buy a lot of ear plugs for the price difference LOL

That thing looks awesome and sounds (quietly) like a great machine, but I don't have enough amps in the whole shop to get even near 15hp, much less the money for that beast. I wish I did, though!

I don't know where you live but if you have neighbors and live in a city, quiet is essential.

They do make a 7.5hp version. Less money, less amps, same quality, same design, less air, less output.

 

[mm08822]

Oh boy, another air compressor question.

5 cfm is NOT going to run a die grinder continuously or for long.

And you say, "But the manufacturer says it only uses 4 cfm. Why is a 5 cfm air compressor not enough to run a 4 cfm air tool?"

Because air tools are 'rated' on a 15 second use in a one minute period.

So that 4 cfm rated die grinder is actually using air at a rate of about 20 cfm. These are example numbers but close to general real world numbers.

A bigger air tank let's you run your air tool a little longer before the compressor pump starts up and tries to refill the tank, but takes longer to refill (among other trade offs).

The rating on the compressor pump is what matters most for sustained air tool use. But check the motor and pump duty cycle, as a lot of units are NOT rated for continuous usage.

A 120v air compressor is only going to give you about 5 cfm or so, as there is only so much electrical power available from the outlet.

So realistically, if you want to run an air die grinder or air sander or a full-sized spray gun (nit an air brush or a small detail gun), you are looking at getting a 240v machine.

Those typically start at 60 gallon and '3 hp' which usually can provide about 10-11cfm @90psi. But as I said, check the duty cycle. And that size unit will still not have enough air capacity to run a die grinder for very long.

$500 is not going to get you even that size unit nowadays IMHO, unless you luck into a deal.

About 8 years ago Tractor Supply had a Black Friday deal on a 60 gallon 10 cfm or so Dewalt air compressor for under $500 IIRC. Last I saw, that unit or similar is now over $800 or so. And the old sale was maybe $100 or so off, not $300+ off.

This is all for reciprocating air compressors, scroll compressors are usually quieter and a better duty cycle rating but cost much more. Eastwood has (or had) a small scroll air compressor, but that was about $2k last checked.

The 25% duty cycle for consumption rating explains a lot!!!! I googled it and for certain, that is the case. Two different needs shooting a nailer or blowing up a tire vs. continuous grinding, sanding or painting. Forget about sand blasting.

I've seen the challenge using a simple die grinder and air hammer continuously.

 

[Sanderguy777]

The 25% duty cycle for consumption rating explains a lot!!!! I googled it and for certain, that is case. Two different needs shooting a nailer or blowing up a tire vs. continuous grinding, sanding or painting. Forget about sand blasting.

I've seen the challenge using a simple die grinder and air hammer continuously.

Yeah, that sounds about right.

My doe grinder can go about 20 seconds before it slows down a LOT.

 

[mm08822]

7.5 hp and above could be a red flag for the Power company. It could also be annoying for everyone else in your house. Just FYI.

Assess your tool needs, most particularly the continuous use types for sizing. I would add 50% to that value and wouldn't consider lower.

ETA: That is, add 50% to the continous 100% usage consumption, not the 25% duty cycle value.

 

[Sanderguy777]

I don't know where you live but if you have neighbors and live in a city, quiet is essential.

They do make a 7.5hp version. Less money, less amps, same quality, same design, less air, less output.

Meh. It is nice, but there are guns kids squealing tires ans revenge engines, and general noise.

I don't live in an apartment with neighbors on top of me, so some noise is fine. and my neighbors are great. Never had any complaints or anything.

 

[Steve_P]

7.5 hp and above could be a red flag for the Power company. It could also be annoying for everyone else in your house. Just FYI.

Assess your tool needs, most particularly the continuous use types for sizing. I would add 50% to that value and wouldn't consider lower.

I have a legit 7.5 HP 240V Quincy, 32A? running. When I bought it 20ish years ago, that was part of the warning in the paperwork- for home use, get approval.... I ignored it and somehow it doesn't even flicker the lights when it kicks in. I don't know how. And it's NOT a soft start, it's violent AF, and draws 100A+ for a split second when it starts as I checked it with a clamp ammeter.

I'm not saying to ignore this warning, but....

Oh, I have plenty of capacity on my main breaker panel.

 

[Steve_P]

The 25% duty cycle for consumption rating explains a lot!!!! I googled it and for certain, that is the case. Two different needs shooting a nailer or blowing up a tire vs. continuous grinding, sanding or painting. Forget about sand blasting.

I've seen the challenge using a simple die grinder and air hammer continuously.

If you want real air consumption numbers for air tools, look at Dynabrade's ratings for their commercial USA made tools as they don't do the "20% duty cycle" BS that everyone else does and doesn't inform you about.

TLDR is most everything is 15-25 CFM for grinders, sanders, belt files....

 

[impactims]

Meh. It is nice, but there are guns kids squealing tires ans revenge engines, and general noise.

I don't live in an apartment with neighbors on top of me, so some noise is fine. and my neighbors are great. Never had any complaints or anything.

Even a residential neighborhood with neighbors that are a stone throw away could be a problem, depending on what kind of people you are dealing with. My motorcycle in the morning is a problem for example. Once you get enough power to supply air to the kinds of tools you are talking about, sound will likely need to be dealt with. Rotary Screw compressors are silent.

 

[mm08822]

I have a legit 7.5 HP 240V Quincy, 32A? running. When I bought it 20ish years ago, that was part of the warning in the paperwork- for home use, get approval.... I ignored it and somehow it doesn't even flicker the lights when it kicks in. I don't know how. And it's NOT a soft start, it's violent AF, and draws 100A+ for a split second when it starts as I checked it with a clamp ammeter.

I'm not saying to ignore this warning, but....

Oh, I have plenty of capacity on my main breaker panel.

Well you got lucky!! Good for you.
Depends where you are on the grid and what other loads are running.

In a development where 4-5 houses share a 25kva pad mount xformer with ac running, it would be noticed.

 

[MoonRise]

Yeah, that is what I'm thinking. Only other way is if I got a used one cheap, but then I might just be bringing a time bomb into the shop. literally. I really don't get why they don't make tanks from aluminum ...

Why no aluminum pressure vessels?

There are some (scuba tanks are one), but like most things in life there are trade offs.

Aluminum can still corrode, the strength when welded is often much less than welded mild steel (most air tanks are welded together, except scuba tanks are typically not made that way), and aluminum is fatigue strength and life limited (just like bending a paper clip back and forth to cause failure). Among just a few of the trade offs for aluminum versus steel.

One thing that I have noticed is that 'good' air tools often use less air than cheap air tools. They still use a lot of air, just less than the cheaper tools.

Even a compressor that supplies an honest 20 cfm @ 90 psi will not be able to keep up with continuous use of air hungry tools like a sander or die grinder. And is going to be limited for media blasting. May or may not be able to keep up with a full sized spray gun.

A real 5 hp motor running the compressor pump is usually going to get you less than 20 cfm @ 90 psi. A 7.5 hp motor on an 80 gallon unit (like the two-stage IR mentioned above) should just be above that 20 cfm threshold.

And good mention of take your hungriest air tool and find out the real continuous air usage needs and add 50% to that to find what you 'need' as far as air supply for continuous usage.

Example: die grinder at 4.5 cfm @ 90 psi rated is probably pulling air at 23 cfm continuously. Add 50% and your air needs are ~35 cfm @ 90 psi to run that die grinder continuously with some margin and having the compressor able to cycle on and off somewhat during usage.. That's a LOT of compressor!

Remember my previous mention of compressor duty cycle ratings too, many compressors are rated at a 25-50% duty cycle only. The pump and motor need time to cool off during usage.

And we haven't even gone into flow restrictions for all the things in the air supply path between the compressor and the air tool. Fittings, the air hose and piping itself, filters, air dryers, etc.

Continuous usage of air tools and not stopping and waiting for the air tank to refill before continuing to use the air tool is what calls for the BIG air compressor CFM needs.

 

[finn]

Yeah, that is what I'm thinking. Only other way is if I got a used one cheap, but then I might just be bringing a time bomb into the shop. literally. I really don't get why they don't make tanks from aluminum ...

Aluminum doesn’t have infinite fatigue life like steel, because of what’s called “creep” induced by repetitive loads. It eventually develops stress cracks.

Aircraft require regular inspections. Aluminum rods are used I some racing engines, but are replaced on a regular basis.

 

[Steve_P]

Well you got lucky!! Good for you.
Depends where you are on the grid and what other loads are running.

In a development where 4-5 houses share a 25kva pad mount xformer with ac running, it would be noticed.

Good point. I didn't mention that I live in a subdivision with 29 houses and I have 200A service; worst case I'd be using 60A not including the compressor. I didn't think it was unreasonable to expect a millisecond at 90-100A and then 32A running with 200A service, so I didn't ask permission.

 

[no704]

This little guy keeps up pretty well!