Air Compressor Buyers guide

[GN SBS]

Hi folks,

My birthday is coming up and I'm thinking of asking my folks and my wife to chip in for an air compressor for the garage.

I only found 1 old post on this topic, so I thought I'd try to get a longer buyers guide post going here.

My primary use will be to run air tools and I am not intending to do any painting, sand blasting, powder coating, etc... so I don't need a high budget unit. The unit will be located in the rafters of my detached garage.

What should I look for in terms of specifications/options?

I'd probably lean towards a Craftsman unit, but if anyone has comments on this please chime in.

thanks!
Scott

 

[xlr8ngn]

Make sure it is a two stage compressor with intercooler. There are vertical tank mounted and horizontal. Vertical units take up less floor space but are typically stationary. Horizontal units normally have wheels and can be rolled around. Get as large a tank as you can stand. If you get a small tank, the compressor will be starting and stopping very frequently and this is very hard on the electric motor. Get 230V single phase and run the wiring if you are going to leave it stationary. Get 115 volt if you get one to move around. 3HP is the minimum I would go, and 7HP would be maximum. Make sure that the unit is at least rated for 175 PSI. The lower pressure rated compressors are typically cheap and will not last long. If you need less pressure, you can regulate it down with an in-line regulator or you can adjust the pressure switch. Try and get one with a cast Iron cylinder if you can, or a one piece aluminum cylinder and head with cast iron sleeve (no head gasket). FYI, a real industrial 5hp compressor starts around $1500.00. You do not need one that heavy duty. You can probably get one for about half that. Also, see if you can get a compressor with larger displacement. This means the compressor itself will turn slower and will last longer. The way manufacturers save money is to use a small displacement compressor and spin it really fast to get the volume up.

 

[V6RACER]

Make sure it has a cast iron pump.. The aluminum pumps do not last as long. Check out www.grainger.com and search for air compressors.

 

[GN SBS]

Any hope of finding a decent unit for $500 or less?

Scott

 

[V6RACER]

Look at the 4B236 @ $481.50 plenty for a home shop running two or three air tools together.. (impact gun, air wrench)

 

[Brian Mc]

A 2 stage is not needed for air tools. Go with a 60 gallon with about 10-11 SCFM. you only need the 135 PSI compressor. A 2 stage is needed when heavy sandblasting is done. I'd look into Ingersoll-Rand compressors. HTH

 

[Brian Mc]

There are many in this size range for less than 500 bucks.

 

[SuperSix]

I can recommend you DON'T get a Craftsman unit. I have the older (~3-4yrs) 100PSI 5HP 20Gal unit..

pressure adjuster leaks
drain valve froze - had to replace
LOUD
Insufficient CFM to paint/various high-volume tools

In retrospect, I would spend a bit more to get a nice vertical unit, check out

http://www.harborfreight.com
http://www.northerntool.com/

I won't buy another Craftsman compressor.

 

[Vendor Defendor]

i have a craftsmen 30 gallon 5 or 6 hp... works great for me, was less than 300 too...

-neil

 

[gn1220]

Don't buy an oil-less. Spend the extra $ and get one that will last.

 

[tom h]

I too, favor a compressor with a conventional oil filled crankcase, pulley driven, with a relatively slow rotating compressor. The better brands are conservatively rated, and you'll get "real honest 10 scfm" vs "peak cfm" or some such crap.

I've been using a contractor's wheelbarrow style, made in USA , Emglo brand for a few years. It was expensive ($600 ?), but has been durable and completely reliable.

Mine is rated 8 scfm, and has been able to operate any pneumatic tool I own (drill, 1/2" impact wrench, etc) . Some types of pneumatic belt sanders are even higher cfm though, so check carefully

Continuous motor horsepower is a good indicator of how much scfm a compressor can supply, no matter what the "cfm" rating claims.

My Emglo has a 1.5 HP motor, which is about the largest you run @ 115 volts and not blow a 20amp breaker. I think 1.5HP is the smallest motor I'd recommend.

A 1.5HP motor could be a problem if you have only 115volt, 15amp breakers & AWG14 house wiring. And even with 20amp/AWG12, you couldn't run another big load on the same circuit (like a refrigerator or saw).

 

[GN SBS]

Thanks for the continued good feedback.

My breaker to the garage is 20amp, but thanks for the note on current-- that's a great addition to this post.

Any more recommended lower budget units?

I'd like to mount it in the rafters-- any snags with this I should be aware of?

thanks,
Scott

 

[Nashty]

(1) HP = 575 watts

575 watts / 120 volts = 4.8 amps

So... 5HP = 23.9 amps @ 120 volts.

Realize though that most motors are overrated and most local voltage is higher than 120.

I have a 4.5 HP Coleman horizontal 25 gallon tank unit that I keep pretty busy with the air grinder and cut off wheel. Sometimes it runs 30 minutes straight withougt complaint. It has the option to run 230V but my welder is on that plug so it stays 110. It has a 20 amp circuit and has never tripped. It is wired with 12-2 wire (the wire is about 15' to the box).

 

[tom h]

Originally posted by Nashty
(1) HP = 575 watts

575 watts / 120 volts = 4.8 amps

So... 5HP = 23.9 amps @ 120 volts.

Mmm, my CRC handbook (and several web sites also) list the conversion as

1 HP = approx 750 Watts = 6.5 Amp @ typical 115 Volt
3HP = approx 19.5 Amp @ typical 115 Volt.

This is only if the the electric motor had perfect 100% efficiency, turning all it's electrical power into mechanical power.

Electric motor efficiency is fairly complicated, depending on the load being turned, how weel motor's matched to the load, type of motor design, etc. I think 70-80% is a typical effciency for an "average" low HP consumer motor.

So theoretically an "honest" 2 - 2.5 Horsepower could be delivered from a 115V / 20A outlet .

BUT ... a motor will draw a much larger current inrush when starting up. No good if the motor trips the breaker when you try to start it!

I guess I'm a bit skeptical that the Coleman motor is an "honest" continuous 4.5HP motor ... maybe during the momentary high current @ startup, it draw 4.5HP ! Like the tiny vacuum cleaners that claim "3 HP Peak power" !

A better indicator of "oomph" might be the continuous rated current on the motor nameplate, which I believe is required by UL.

 

[tom h]

No one's mentioned Campbell-Hausfeld brand compressors. Their Most of their units aren't "heavy duty" contractor type, but some of their units looked reasonable. I recall once looking at their "cast iron" series, with slow turning, oil bath compressor.

Some of my less frequently used air tools are Campbell-Hausfeld (when I can't justify an $$ Ingersoll-Rand tool), they have performed well.

I just glanced at the Campbell-Hausfeld web site, so beware because they do use the "PEAK horsepower" scam.

I also noted some compressor mfrs use a CFM rating at both 40 & 90 psi. The 90 psi is the only one that matters , since that's what air tools are typically operated at.

 

[J Banning]

Something to think about...

The SEARS Craftsman stuff usually has a very good warranty (lifetime on their hand tools), and they've got stores (for repair/returns) in practically every town now.

I've been using a set of Campbell-Hausfeld air tools now. Air ratchet, die grinder, and cuttoff wheel. Each was $30. They all are still working fine. Not the best, but for $30 I can't complain.

-B

 

[machinegun]

I have a campbell hausfield, portable verticle oiless 5 hp 30 gallon tank compressor. I purchased this at wal-mart for 275.00 4 years ago. I use an impact, air ratchet, drill cutoff tool and die grinder. Using the cutoff tool or die grinder I sometimes have to wait a few seconds between runs. I have had no problems and has run like a top. It is easy to use and I can throw it in my trailer or into the back of the suburban. It has been used for roofing, cleanning and some blasting. I use the heck out of it and it still keeps on going. This thing has worked like a swiss time piece. It is noisy but I am used to it.

 

[scottyb]

Originally posted by machinegun
I have a campbell hausfield, portable verticle oiless 5 hp 30 gallon tank compressor. I purchased this at wal-mart for 275.00 4 years ago. I use an impact, air ratchet, drill cutoff tool and die grinder. Using the cutoff tool or die grinder I sometimes have to wait a few seconds between runs. I have had no problems and has run like a top. It is easy to use and I can throw it in my trailer or into the back of the suburban. It has been used for roofing, cleanning and some blasting. I use the heck out of it and it still keeps on going. This thing has worked like a swiss time piece. It is noisy but I am used to it.

Just what I wanted to hear. I was just looking at one there that comes with various tools. I'm not a hard core user, so I think it will do for me. Thanks.

 

[GN SBS]

How about some detail on the pros and cons of oil-less v. oiled compressors?

I'll start:
Oil-less (pros): less expensive, one less item to add to the routine maintenance list.

Oil-less(cons): shorter life ? louder? Help me understand the difference for a non- high dollar compressor.

thanks,
Scott

 

[tom h]

Scott,

I think you've summarized the esssential differences between oil & oilless compressors, although quantitative specifics are going to be hard to come by.

Let me add one more:

Initially I bought an approx ¾-1 HP oilless Emglo, 120 volt. Most oilless seem to be direct drive, not belt, BTW.

I had a lot of trouble with motor startup on my 120 volt circuit. Maybe 1 of 3 times, it would trip my 20A breaker.

I upgraded to a larger 1.5HP, but slower rotating oil compressor (also Emglo), and it's been fine & doesn't overtax my breaker at startup.

The direct drive motors (typical of oilless) seem to have higher inrush currrents at startup. I suppose it's like being stuck at 3rd gear all the time, with none of the torque multiplication of a pulley system. Even on a pulley system, the electric motor is more likely to be a slower 1725 RPM unit, whereas a direct drive oilless is more likely to be a 3400-3700 rpm unit. Exceptions probably exist.

The oil changes required are not a big deal. Unless you operate in dusty outdoor conditions, 6 - 12 month oil changes are OK. There's probably many users who don't change oil for a lot longer!

To make oil changes un-messy, I installed a 3" long pipe nipple into the crankcase's drain. Then installed a 45º female elbow on end of nipple, and a pipe plug into elbow. (all 1/8" NPT size).

With the new oil drain projecting a few inches away from the crankcase, it's easy to put a cup underneath when draining; only requires a few 100 cc's anyway.

Oilless units (even of the heavy duty "pro" type), are more suited to be used for carpenters' pneumatic nail guns (not air tools) , IMO.