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Compressor Questions

alex123

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Jan 16, 2019
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177
Location
USA
Hello,

I am buying a 30 gallon air compressor for home auto repair and maintenance. I have a couple of questions:

(1) I am planning on using this compressor for automotive use only, and that in my garage. I have some really good quality Milwaukee automotive tools, but I also want (and need!) and air compressor. Given that I'll only be using the compressor say once a month, do I really need to go with a oil-lubed compressor? Or, can I go oil-less?

(2) This is my first compressor setup,and I want to get everything in one go from the big box store. What all do I need to ensure I get maximum performance out of my tools, and to be able to maintain both the compressor and the tools? Below are some of the items that came to mind, but I have questions regarding these:

(i.) Air hose - I'm looking at 3/8" 25 feet... Any type of material, and/or brand I should prioritize?
(ii.) Fittings/Connectors- I have no clue which fittings to get for max. air flow from the compressor to my tool. Please advise.
(ii.) Fittings/Connectors Part 2 - The 360 degree swivel air tool fittings... Are these any good? If so, which diameter should it be? What is a good quality brand?
(iii.) Inline Air Filter - I know absolutely nothing about these, but have been told I should add one. Do they all work the same? Can I pick up any random one? Is it easy to connect? Any information about these would be helpful.
(iv.) Miscellaneous - Any items I missed that I should add to the list?

Thank you in advance for your assistance,
 
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GeoBruin

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You don't say what you actually need the compressor for. Is it blowing things off and filling tires, running impact wrenches and air hammers, or running die grinders and sanders? What you're going to hear on this forum is that an oilless compressor will only handle the first. You will hear that running air tools requires a higher flow compressor, high flow fittings, etc. Truthfully, you can occasionally run impacts, air ratchets, air hammers etc for short bursts on even a small pancake compressor. However, if you start to use these tools often, you will get tired of waiting on your compressor and the compressor will run constantly.

Running constant use tools like grinders and sanders simply requires too much air for a small oilless compressor. You will drain the tank quickly and it will never get a chance to fill back up to the point where it will provide the regulated pressure you're asking for. You will be disappointed if you try.

A 25 ft. 3/8" hose is great. As for fittings, since your compressor will limit you to tools that do not require massive flow, standard 1/4 npt industrial fittings are fine. If you wanted to run a big 3/4" impact or perhaps even one of the bigger 1/2" impacts, you would probably benefit from v-style high flow fittings but again, that doesn't seem like it's in the cards for the type of compressor you're contemplating. There's really nor harm in updrading fittings other than the cost.

Your compressor will probably come with a regulator built in based on the type it sounds like you're shopping for but a water trap/filter is a nice addition. Unfortunately, again, you will hear on this forum that you need an elaborate manifold of hard lines between your compressor and the filter to help cool and concense out the water in your air lines but that's also probably not in the cards based on what it sounds like you have in mind. If you simply want to filter out particulates and catch some water, it will work okay. I don't have any specific recommendations. As usual, they range from 10's to 100's of dollars based on what your goal is, however the really expensive setups have multiple stages for particulate, oil, and water filtration and really do require you cool the air sufficiently for them to work as intended. A "piggyback" filter regulator downstream of your compressor just before your hose is probably a good compromise for not too much money.

I guarantee you will have people recommending 5+ HP, 240 volt, 80 gallon compressors withing minutes, so be prepared for that. But think seriously about whether you really need to head down that path for what you want to achieve in your shop. It's kind of a slippery slope.

Good luck.
 
Last edited:

Walkers

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My first compressor was a little roll around oil lubed compressor that ran on 120 volts. It was a darn fine machine. I worn it out over 15 years of hard use.
I bought my dad a similar sized oilless unit. It is so noisey it makes you not want to use it.
I strongly recommend a oil lubed unit, far more pleasant to use.
 

WheelsNT

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May 8, 2008
Messages
77
Your frequency of use sounds like mine. As mentioned above, It depends on what you want to do. I wanted a good 1/2“ impact and thought I needed a compressor. But a compressor big enough to run a powerful impact is $$$. In the end I got DeWalt’s biggest 1/2” cordless impact for much much less money. It’s strong enough to break things if you’re not careful, so it’s enough for my needs. So I saved like $1000 and I don’t have to maintain the compressor.

I was influenced by a number of threads on here where people said they hadn’t used their air tools at all or very seldom after getting cordless tools.
 

GeoBruin

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My first compressor was a little roll around oil lubed compressor that ran on 120 volts. It was a darn fine machine. I worn it out over 15 years of hard use.
I bought my dad a similar sized oilless unit. It is so noisey it makes you not want to use it.
I strongly recommend a oil lubed unit, far more pleasant to use.
This has generally been true for a long time, but:

1) mufacturers are finding ways to make oilless units very quiet these days. California Air Tools is a good example but there are others as well as clones (including Harbor freight) that are in the high 60s to 70 dB. That's really freaking quiet. That's their whole marketing campaign is how quiet they are. And a CAT oilless machine making 5 cfm at 70db is pretty hard to ignore except for the longevity prospects which I'm not qualified to speak on.

2) Other than a few big compressors with big motors turning pumps at 500 or 600 rpm, most of the affordable (for the home shop guy) oil lubed compressors are running the pumps at crazy high speeds to get their advertised cfm and they are crazy loud.

My last compressor was a 120 volt 2HP Quincy (manufactured in 2019) and it was okay, but certainly not quite and no where near as quiet as a CAT or similar. My current compressor is a 5 hp 60 gallon Bellaire/Atlas Copco and even with a 90 degree elbow and a Solberg filter/silencer, it's even louder than the little Quincy.
 

dnschmidt

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Let me be "that guy." If all you're going to do is fill up your tires whatever you chose will be fine but unless going deaf seems like a good idea go with a belt drive in whatever you get.


Now time to be the villain. If you want to paint cars, use die grinders use the much superior to electric air sanders, unless you're going with the Mirka Deros electric system, which you sure as hell aren't as they cost more than a compressor you DO NEED THE 5HP 80 GALLON TWO STAGE COMPRESSOR. Here are facts.

My SATA, Iwata and DeVilbiss professional level spray guns require 17scfm of air. Notice the period at the end of that sentence. My air die grinders (which I now seldom use since the Milwaukee M12 with the 6.0 battery has just about superseded them) require at least that much air. So too do my Airvantage and Dynabrade random orbit sanders as well as my Mug Hogs and air files. Yes, in short bursts you can use an air chisel or impact with a smaller compressor but if you're trying to cut off a quarter panel or take apart an engine with one forget about it.

This question is asked at least twice a month and likely more often than that and the answer NEVER CHANGES. Physics is physics and you can't get something for nothing. Oh! By the way if you want to sandblast something then you're going to need at least 7 1/2HP to power that. The world doesn't care what you're budget is all it cares about is SCFM. Life ***** and then you die. See, I told you nothing changes.
 

Neggy

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May 30, 2021
Messages
754
I have an old Craftsman compressor, probably 20 years old, it won't run high demand stuff for long, but it has served me well.

The only thing I have used it for in the last year was to raise and lower the motorcycle lift, my Milwaukee addiction has rendered most of my air tools obsolete in the home garage.

I have never had the need for a super nice compressor at home ( compressor type and tank size), the shop is a different story, when I ran a production floor with 20 techs using air tools it was a different world...

Figure what tool you will need the most SCFM for (DA sander? Sand Blaster? ) then increase it by 50%. Do the same for the tank size, some of this stuff can drain a tank in a minute.... die grinders, DA sanders, paint guns.... high flow long duty cycles.
 
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alex123

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Jan 16, 2019
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USA
You don't say what you actually need the compressor for. Is it blowing things off and filling tires, running impact wrenches and air hammers, or running die grinders and sanders? What you're going to hear on this forum is that an oilless compressor will only handle the first. You will hear that running air tools requires a higher flow compressor, high flow fittings, etc. Truthfully, you can occasionally run impacts, air ratchets, air hammers etc for short bursts on even a small pancake compressor. However, if you start to use these tools often, you will get tired of waiting on your compressor and the compressor will run constantly.

Running constant use tools like grinders and sanders simply requires too much air for a small oilless compressor. You will drain the tank quickly and it will never get a chance to fill back up to the point where it will provide the regulated pressure you're asking for. You will be disappointed if you try.

A 25 ft. 3/8" hose is great. As for fittings, since your compressor will limit you to tools that do not require massive flow, standard 1/4 npt industrial fittings are fine. If you wanted to run a big 3/4" impact or perhaps even one of the bigger 1/2" impacts, you would probably benefit from v-style high flow fittings but again, that doesn't seem like it's in the cards for the type of compressor you're contemplating. There's really nor harm in updrading fittings other than the cost.

Your compressor will probably come with a regulator built in based on the type it sounds like you're shopping for but a water trap/filter is a nice addition. Unfortunately, again, you will hear on this forum that you need an elaborate manifold of hard lines between your compressor and the filter to help cool and concense out the water in your air lines but that's also probably not in the cards based on what it sounds like you have in mind. If you simply want to filter out particulates and catch some water, it will work okay. I don't have any specific recommendations. As usual, they range from 10's to 100's of dollars based on what your goal is, however the really expensive setups have multiple stages for particulate, oil, and water filtration and really do require you cool the air sufficiently for them to work as intended. A "piggyback" filter regulator downstream of your compressor just before your hose is probably a good compromise for not too much money.

I guarantee you will have people recommending 5+ HP, 240 volt, 80 gallon compressors withing minutes, so be prepared for that. But think seriously about whether you really need to head down that path for what you want to achieve in your shop. It's kind of a slippery slope.

Good luck.
I should have shared more specifics on the intended automotive use (My apologies!). So basically, I already have a few cordless M18/M12 tools (1/2" impact, ratchet, stubby impact). The MAIN tool I absolutely need this compressor for is a air hammer. Unfortunately, there are no viable cordless options that are both powerful, and compact, for tight automotive spaces. There will be no painting, sanding, sand blasting, whatsoever. If a 30 gallon compressor can pull off using a die grinder, and cut-off tool (Not sure??), then I can by those as pneumatic, but I really don't know if a 30 gallon can run those tools?

On a 30 gallon tank, stepping up to oil-less is not a major cost upgrade, so all good, I can go oil-less :)

For the air line filter, that's fine too, I can go with something in the ~$50 dollar range.... no sense in breaking the bank for a expensive air filter on this size compressor.

As for the fittings, I will have to Google the v-type you are referring to, as pneumatic tools are new to me. But, if the cost difference is minor, I'll be happy to make the step up to the v-style.

What are your thoughts on my tool lineup, and the tools I want to run off this compressor, please?


My first compressor was a little roll around oil lubed compressor that ran on 120 volts. It was a darn fine machine. I worn it out over 15 years of hard use.
I bought my dad a similar sized oilless unit. It is so noisey it makes you not want to use it.
I strongly recommend a oil lubed unit, far more pleasant to use.
It seems like on a 30 gallon tank, stepping up to oil-less is only about $200 more... if the difference in sound is that much, that's a no brainer at that point... I'll do oil-less. Thank you for sharing! :)

Your frequency of use sounds like mine. As mentioned above, It depends on what you want to do. I wanted a good 1/2“ impact and thought I needed a compressor. But a compressor big enough to run a powerful impact is $$$. In the end I got DeWalt’s biggest 1/2” cordless impact for much much less money. It’s strong enough to break things if you’re not careful, so it’s enough for my needs. So I saved like $1000 and I don’t have to maintain the compressor.

I was influenced by a number of threads on here where people said they hadn’t used their air tools at all or very seldom after getting cordless tools.
My apologies for not being more clear on the details... You are correct, simply saying "automotive" is very broad. I'll be using this for repairs and maintenance only. I already have a few cordless M18/M12 tools (1/2" impact, ratchet, stubby impact). The MAIN tool I absolutely need this compressor for is a air hammer. Unfortunately, there are no viable cordless options that are both powerful, and compact, for tight automotive spaces. There will be no painting, sanding, sand blasting, whatsoever. If a 30 gallon compressor can pull off using a die grinder, and cut-off tool (Not sure??), then I can by those as pneumatic, but I really don't know if a 30 gallon can run those tools?



I have an old Craftsman compressor, probably 20 years old, it won't run high demand stuff for long, but it has served me well.

The only thing I have used it for in the last year was to raise and lower the motorcycle lift, my Milwaukee addiction has rendered most of my air tools obsolete in the home garage.

I have never had the need for a super nice compressor at home ( compressor type and tank size), the shop is a different story, when I ran a production floor with 20 techs using air tools it was a different world...

Figure what tool you will need the most SCFM for (DA sander? Sand Blaster? ) then increase it by 50%. Do the same for the tank size, some of this stuff can drain a tank in a minute.... die grinders, DA sanders, paint guns.... high flow long duty cycles.
Thankfully I have a M 18/M12 lineup (Impact wrench, ratchet, etc.) . There will be no sand blasting, DA sander, or painting..... at all actually. The main reason I'm getting the compressor is to run a air hammer.


The only worry with cheap oil less compressors is noise. Some of the newer and more expensive ones aren't bad.

Thanks for sharing! You are correct, and that seems to be what I've been hearing from everyone. At about $200 more for oil-less... I think I'll get the oil-less based on your, and others, advice. Thank you again! :)
 

marinusdees

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Oct 30, 2012
Messages
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Edgewood, Washington
Hello,

I am buying a 30 gallon air compressor for home auto repair and maintenance. I have a couple of questions:

(1) I am planning on using this compressor for automotive use only, and that in my garage. I have some really good quality Milwaukee automotive tools, but I also want (and need!) and air compressor. Given that I'll only be using the compressor say once a month, do I really need to go with a oil-lubed compressor? Or, can I go oil-less?

(2) This is my first compressor setup,and I want to get everything in one go from the big box store. What all do I need to ensure I get maximum performance out of my tools, and to be able to maintain both the compressor and the tools? Below are some of the items that came to mind, but I have questions regarding these:

(i.) Air hose - I'm looking at 3/8" 25 feet... Any type of material, and/or brand I should prioritize?
(ii.) Fittings/Connectors- I have no clue which fittings to get for max. air flow from the compressor to my tool. Please advise.
(ii.) Fittings/Connectors Part 2 - The 360 degree swivel air tool fittings... Are these any good? If so, which diameter should it be? What is a good quality brand?
(iii.) Inline Air Filter - I know absolutely nothing about these, but have been told I should add one. Do they all work the same? Can I pick up any random one? Is it easy to connect? Any information about these would be helpful.
(iv.) Miscellaneous - Any items I missed that I should add to the list?

Thank you in advance for your assistance,
 

marinusdees

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Messages
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Location
Edgewood, Washington
Last I knew, oil less technology was Teflon coated piston rings and brass cylinder liners. The Teflon sacrifices itself to the brass and eventually wears out. Much sooner than an oil filled compressor. For occasional use maybe not critical. Also, oil less generates considerably more heat. Again maybe not critical to your use.
 

shadetree_mech

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Illinois
Have you considered maybe going with a used 60 gal compressor, or do you need the portability of the 30 gal? Some of the other things you are wanting to use will **** a 30 gal empty quick. By using a 60 gal, you won't be limiting yourself the volume/psi needed in some tools, or maybe use the savings from used to buy better tools?

Just an option I thought I'd throw out there. I just missed out on a 80 gal 2 stage for $425 that was in great shape by minutes, so there are deals out there.
 

Walkers

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Just make sure the the CFM rating of the compressor is as big or bigger tgan the CFM rating of the biggest air user tool that you want to run.
 
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redmondjp

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Just make sure the the CFM rating of the compressor is as big or bigger tgan the CFM rating of the biggest air user tool that you want to run.
As stated in an earlier post above, the listed flow rates for most air tools are wildly inaccurate. Most users can confirm this. How? Take the typical 3.2HP (actual, used to be advertised as 5-6.5HP, before the class-action lawsuit) single-stage 60-gallon box store air compressor, that says that it can flow somewhere around 11cfm @40psi and 9cfm @90psi (going from memory here, but those numbers are close).

Now, connect that compressor to a die grinder, air sander, or needle scaler that claims it only requires 4.5cfm on the box. Then see how many minutes you can actually run that tool before your compressor is down to 80psi and spitting water out the end of the hose. It becomes readily apparent in about 10 minutes of continuous use that the compressor can NOT keep up with the demands of the tool, even though the numbers would indicate that the compressor can flow twice what the tool says that it needs.

So your recommendation falls apart in real-world testing.

Today's 30-gallon oil-lubed belt-driven single-stage compressors have essentially the same size motor and pump as the 60-gallon units. This is great for those with smaller shop spaces, but it doesn't help when trying to use a tool that requires more air than the pump can provide. The bigger the receiver, the more minutes of continuous use you can get out of the the tool (before allowing the compressor to catch up). So there is a tradeoff there. For impact tools that are only used for less than a minute, no real difference. But if you are trying to use a cutoff tool or air sander for more than 2-3 minutes at a time, the bigger tank will be noticeable. No free lunch here, as the pump still can't keep up with the tool, but you have a few more minutes of reserve air to use up first with the larger tank.
 

65ranchero

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Here is a site where you can shop and compare all the types of compressors .
Have fun!
This is the one I have https://www.aircompressorsdirect.com/BelAire-4916V-Air-Compressor/p110292.html
Being retired as auto tech and having air tools it was a good fit for me. I'm glad I got it when I need the air grinder ,air chisel, die grinder and cut off wheel.
it sits in a 2 bay garage and at times it a little on the noisy side but part of that is because it sits next to a wall and nothing around to dampen it ,I was able to knock the noise down a little with some dampening material.
 

Walkers

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As stated in an earlier post above, the listed flow rates for most air tools are wildly inaccurate. Most users can confirm this. How? Take the typical 3.2HP (actual, used to be advertised as 5-6.5HP, before the class-action lawsuit) single-stage 60-gallon box store air compressor, that says that it can flow somewhere around 11cfm @40psi and 9cfm @90psi (going from memory here, but those numbers are close).

Now, connect that compressor to a die grinder, air sander, or needle scaler that claims it only requires 4.5cfm on the box. Then see how many minutes you can actually run that tool before your compressor is down to 80psi and spitting water out the end of the hose. It becomes readily apparent in about 10 minutes of continuous use that the compressor can NOT keep up with the demands of the tool, even though the numbers would indicate that the compressor can flow twice what the tool says that it needs.

So your recommendation falls apart in real-world testing.

Today's 30-gallon oil-lubed belt-driven single-stage compressors have essentially the same size motor and pump as the 60-gallon units. This is great for those with smaller shop spaces, but it doesn't help when trying to use a tool that requires more air than the pump can provide. The bigger the receiver, the more minutes of continuous use you can get out of the the tool (before allowing the compressor to catch up). So there is a tradeoff there. For impact tools that are only used for less than a minute, no real difference. But if you are trying to use a cutoff tool or air sander for more than 2-3 minutes at a time, the bigger tank will be noticeable. No free lunch here, as the pump still can't keep up with the tool, but you have a few more minutes of reserve air to use up first with the larger tank.
I sense a little frustration on your part. It is super easy to avoid any problems like those. Just buy as big a compressor as you can find. I run an IR T-30 with a 7.5 horse motor on an 80 gallon tank. The only thing that eats too much air for me is my sandblast cabinet.
 
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alex123

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Last I knew, oil less technology was Teflon coated piston rings and brass cylinder liners. The Teflon sacrifices itself to the brass and eventually wears out. Much sooner than an oil filled compressor. For occasional use maybe not critical. Also, oil less generates considerably more heat. Again maybe not critical to your use.
Thank you for sharing this. Yes, I will most likely go with oil lubricated compressors.
 
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alex123

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Have you considered maybe going with a used 60 gal compressor, or do you need the portability of the 30 gal? Some of the other things you are wanting to use will **** a 30 gal empty quick. By using a 60 gal, you won't be limiting yourself the volume/psi needed in some tools, or maybe use the savings from used to buy better tools?

Just an option I thought I'd throw out there. I just missed out on a 80 gal 2 stage for $425 that was in great shape by minutes, so there are deals out there.
Unfortunately, anything beyond the portable 30 gallon will not work for my situation (...a host of reasons which I won't bore you with). Thank you for the suggestion, though, and if it was an option, you are correct, that would have been my best option.
 
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alex123

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Just make sure the the CFM rating of the compressor is as big or bigger tgan the CFM rating of the biggest air user tool that you want to run.
I plan on using an air hammer, primarily. It appears that the 30 gallon won't keep up with die grinders and or cut off tools. Out of curiosity, will a cut-off tool run continuously for a minute on a 30 gallon compressor? If so, that may be all I need. I'm not looking to have endless air supply from a 30 gallon tank, just something that can handle light duty work.
 

GeoBruin

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I plan on using an air hammer, primarily. It appears that the 30 gallon won't keep up with die grinders and or cut off tools. Out of curiosity, will a cut-off tool run continuously for a minute on a 30 gallon compressor? If so, that may be all I need. I'm not looking to have endless air supply from a 30 gallon tank, just something that can handle light duty work.
I gave you the tools to answer this very question in this thread:

Post in thread 'Air Hammer - Tank Size' https://www.garagejournal.com/forum/threads/air-hammer-tank-size.481826/post-9105533
 

rlitman

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I plan on using an air hammer, primarily. It appears that the 30 gallon won't keep up with die grinders and or cut off tools. Out of curiosity, will a cut-off tool run continuously for a minute on a 30 gallon compressor? If so, that may be all I need. I'm not looking to have endless air supply from a 30 gallon tank, just something that can handle light duty work.
You can do a lot with a cheap die grinder and a 30 gallon tank. Die grinders use no more air than cutoff tools, and are used in shorter bursts. Use an electric angle grinder for cutting.
 

Walkers

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The question is, how long will it run on a cut, and how long until the next cut? If it works long enough before the tank is depleted, then rests long enough to recover, then you are fine. But if you turn on this tool in the morning and it runs until quitting time, then it won’t. The compressors you are looking at work well for a lot of hobby guys.
 

engineer2

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I've used undersized air compressor for much of my life. It all works, but for shorter periods of time. You might have to take a break every few minutes. 30 years ago I sandblasted a car frame and suspension parts with a 2HP sears compressor often ignoring the 50% duty cycle spec. It worked out fine and all it did was carbon up the head. That compressor is still in use today.
4403659.jpg

For your new compressor you might consider some type of aftercooler to reduce water condensation in your air tools.
 

65ranchero

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I plan on using an air hammer, primarily. It appears that the 30 gallon won't keep up with die grinders and or cut off tools. Out of curiosity, will a cut-off tool run continuously for a minute on a 30 gallon compressor? If so, that may be all I need. I'm not looking to have endless air supply from a 30 gallon tank, just something that can handle light duty work.
To give you a perspective, I had a cheap lock on a cable wrapped around a tree too far for a extension cord or air hose /
I aired up a converted BBQ propane tank to 125 psi and took it along with my short coil hose and my air cut off tool .
figuring that it will be done fast.
hook every thing up and was about 3/4 way through the cut on the lock shank and the air ran out . had to go back and refill to finish the job.

Why am telling the story? it is just to show how much a cut off or air grinder , die grinder can use up in a short time . meaning long run times for under rated compressor!
 

FordTruckWench

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30 years ago I sandblasted a car frame and suspension parts with a 2HP sears compressor often ignoring the 50% duty cycle spec.

Years ago I sandblasted an engine block/heads/pan/brackets/etc with an oil-less 240 volt compressor. Lots of having to stop and wait for the compressor to catch back up. I also used a die grinder to port the heads and polish the chambers almost to a mirror finish. The sandblasting work needed a bigger compressor. The die grinding work could have got by with a 120 volt compressor.

In my view, compressors can be classified into four groups:

1) Those that run from a 120 volt receptacle - probably will be rated to draw 13 amps.
2) Those that run from a 240 volt receptacle - might be rated to draw up to 17 amps.
3) Hardwired compressors (electrical code says that anything using more power than the previous group needs to be hardwired.)
4) Little toys - for example with a 1 or 2 gallon tank.

Ignore all specs beyond the power connection: A manufacturer can up the horsepower rating by simply using an output pipe/fitting with a bigger hole in it. But of course that doesn't actually increase the continuous output. Tank size is important, but hopefully the manufacturer matched it with the compressor so don't shop just on size.

Most of the folks here will suggest a compressor big enough to need hardwiring. But you can get a lot done with a smaller compressor.
 
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alex123

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Years ago I sandblasted an engine block/heads/pan/brackets/etc with an oil-less 240 volt compressor. Lots of having to stop and wait for the compressor to catch back up. I also used a die grinder to port the heads and polish the chambers almost to a mirror finish. The sandblasting work needed a bigger compressor. The die grinding work could have got by with a 120 volt compressor.

In my view, compressors can be classified into four groups:

1) Those that run from a 120 volt receptacle - probably will be rated to draw 13 amps.
2) Those that run from a 240 volt receptacle - might be rated to draw up to 17 amps.
3) Hardwired compressors (electrical code says that anything using more power than the previous group needs to be hardwired.)
4) Little toys - for example with a 1 or 2 gallon tank.

Ignore all specs beyond the power connection: A manufacturer can up the horsepower rating by simply using an output pipe/fitting with a bigger hole in it. But of course that doesn't actually increase the continuous output. Tank size is important, but hopefully the manufacturer matched it with the compressor so don't shop just on size.

Most of the folks here will suggest a compressor big enough to need hardwiring. But you can get a lot done with a smaller compressor.
Thank you for your input. As mentioned previously, unfortunately getting a large, 240v, is not an option for me (many reasons). It seems like the compressor will do most of the work I need. I did the math using Boyle's Law (Thank you @Geo Bruin!), and size wise I think 30 gallons will do as there will be no sandblasting, polishing, etc...
 
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