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Air Compressor

John King

John King

Joined
Aug 31, 2006
Messages
331
Likes
131
Location
Montgomery, TX
Website
www.gulfcoastwoodturners.org
I am in the market for a new air compressor.

I know the importance of most air compressor variables - flow rate at 90 psi and 40 psi, motor horsepower, maximum pressure, etc. But one variable puzzles me a bit - tank size.

What I have learned in shopping around is that many air compressors have the same flowrates, horsepower, etc., but have different tank sizes. Range of tank size is small pancake to HUGE. I am going to stay away from HUGE and go with something in the 20 to 30 gallon range. And now for the questions.

How does tank size affect air compressor performance? All other variables being equal, should I go with a larger tank size? Why? What difference in performance will I see between large (say 30 gallon) and small (say 20 gallon) tank size?

With regard to air compressors, I am looking very seriously at a Campbell Hausfeld air compressor with cast iron, twin cylinder, oil lubricated pump. They have a variety of tank sizes.

Anyone have any experience with or thoughts on Campbell Hausfeld compressors?

As always, appreciate whatever inputs you may have. - John
 
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John:

Check-out the recent Woodcentral thread HERE

Some discussion in this thread about what you are asking.... search on past WC threads on this topic as well (lots of them in Woodcentral archived posts).

Just been there and did that in early December (I went with a Castair compressor [made in USA] but looked seriously at the Campbell Hausfeld cast iron units).

Larger tanks mean greater air ballast and fewer compressor starts & stops. Much of this is what you can afford and fit in the allotted space. In most cases bigger is better, but not always (....resisting urge to tell old girlfriend jokes now...). I also was looking for QUIET (compared to my old Sears oil-less compressor) and found it in a belt-driven, cast-iron, oil lubed unit. World of difference - my wife even said "Thank-you" when she heard the new compressor running!

Good luck with your choice!

Rob
 
John King said:
... I know the importance of most air compressor variables - flow rate at 90 psi and 40 psi, motor horsepower, maximum pressure, etc. But one variable puzzles me a bit - tank size.

How does tank size affect air compressor performance? All other variables being equal, should I go with a larger tank size? Why? ...
Click to expand...

I consider tank size to be quite important, but the size you need is very dependent on the intended use. For a nailer or blow gun, a pancake compressor would probably be sufficient. For a HVLP spray gun where continuous air flow at constant pressure is needed, a two stage compressor on a large stationary tank would probably be what you need. Air sanders are also air hogs so a really big storage tank is necessary. Most everything else falls somewhere between these two extremes. The most important thing that the specs may not always tell you is both short term and continuous air flow ratings -- and that number is greatly affected by the tank size because instantaneous tank pressure determines the instantaneous flow rate and the larger the tank volume, the longer time that the flow rate can be sustained.

You did not specifically ask about motor horsepower or machine rated horsepower, but I would not pay much attention to that bit of information other than its indirect relationship to electrical hookup requirements. It is mainly a bit of advertising fluff. If the other compressor specifications meets your needs, then horsepower adds nothing useful. Sometimes the motor horsepower itself is not given -- instead, a machine rated horsepower is used. If you look at the nameplate of the motors on those machines, you will see that they do not state horsepower. The reason is they are using the NEMA classification of "definite purpose" for the motor -- in other words, their use is dedicated to a particular machine and are considered to be an integral component of it. The thing about compressors that is different than most other machines is that they store energy on a long term basis. Depending on your creativity in expressing how this energy is converted into work, differing numbers for horsepower can be arrived at.

A few years ago there was a class action settlement against all of the compressor manufacturers except for Ingersoll Rand regarding the false statement of rated horsepower. The settlement amounted to not much more than a slap on the wrist and a promise to "play nice" in the future. While horsepower numbers used to be wildly inflated, I still do not pay much attention to them. Everybody who had opted to participate in the suit had the opportunity to choose one of several different "thank you" gifts. I went for twenty-five feet of air hose as a symbolic gesture of appreciation of their thoughtfulness.
 
If you're going to sand with air, go big. If you want to clear dust, apply finish and perhaps do a bit of pneumatic carving, 20 should go. Takes longer to fill that big tank, and you will be draining it after every session, especially if you are applying finish (keeps the water down). I'd rather sand with electrons directly in my wood shop. Now, in a body shop, 'nother story.

Campbell-Hausefeld comes in chintzy homeowner to contractor grade, so buy the higher-priced similarly-featured unit.
 
Don't Overlook the Noise Factor

Aside from all of the other considerations, I have a Porter-Cable compressor that almost requires ear protection when it fires up. Great little portable but not suitable for inside the shop use.
 
John King said:
I am in the market for a new air compressor.

I know the importance of most air compressor variables - flow rate at 90 psi and 40 psi, motor horsepower, maximum pressure, etc. But one variable puzzles me a bit - tank size.

What I have learned in shopping around is that many air compressors have the same flowrates, horsepower, etc., but have different tank sizes. Range of tank size is small pancake to HUGE. I am going to stay away from HUGE and go with something in the 20 to 30 gallon range. And now for the questions.

How does tank size affect air compressor performance? All other variables being equal, should I go with a larger tank size? Why? What difference in performance will I see between large (say 30 gallon) and small (say 20 gallon) tank size?

With regard to air compressors, I am looking very seriously at a Campbell Hausfeld air compressor with cast iron, twin cylinder, oil lubricated pump. They have a variety of tank sizes.

Anyone have any experience with or thoughts on Campbell Hausfeld compressors?

As always, appreciate whatever inputs you may have. - John
Click to expand...

John,

You need to check your data. The only C-H compressors in the 2-stage, twin cylander class are at least 80 gallons and real 5-7 hp on the motors requiring 220 and dedicated 30+ amp circuits.

Larger tanks smooth out the pulses of air put out by the compressor pumps. This is important in spray finishing for material control. You haven't stated what you want the compressor for or your budget, so if you could be more specific, you'll get better answers.

I use an I-R 3 hp single stage unit that puts out 12 CFM @ 90psi which is all I need.

Just a passing note, it's a huge waste of time and money to drain any compressor over 30 gal. size unless it's being taken out of service for a longer period of time. The issue is removal of condensed water and oil vapor from the tank that cause rusting of the tank. This can be done manually using a simple drain valve each day or automatically using an air-actuated drain. I can supply you the information on both when you're ready.
 
air cmpressor

the important part to look for on the label Is what the "SCFM" RATING IS "sustained cubic feet per minute" basically the constant flow of air while the compressor is running at a given pressure 12 scfm @ 90 psi ( as an example)
it is always different than the cfm rating. when you go to purchase air tools, look at the label on the tool for the scfm rating required, if your compressor wont give you that output then your compressor is too small and the tool requires more air than your compressor can supply to make it operate properly.
this is especially important if you are using air sanders or air files that consume alot of air in a short amount of time.
and to offer an opinion in size i would get atleast a 60 gallon tank.
not sure how the 2 stage thing came up but you will pay dearly for a 2 stage unit
 
I have this one: http://www.northerntool.com/shop/tools/product_158284_158284

Adequate for my needs (air body saw, blowing out hollow forms, carving with air die grinders) and it is rock solid, if you use the IR oil and filter (Start up Kit) you get a 2 year warranty.

I love this compressor, no complaints.

Don't skimp on your compressor - you will be kicking yourself for getting a cheapo one.
 
Tank size could be important to you, if you use a lot of air in a short period of time.

I had a 20gal compressor that served me for more than 20yrs. When I was using air in quantity, the compressor ran constantly. Air lines heat up, and condensation is a problem.

In 2007, I purchased a new compressor with an 80gal tank. I've noticed that the condensation of H2o in the lines isn't nearly the problem it used to be.

Both compressors had/have in-line water seperators, but the condensation problem was so acute with the smaller compressor, that it often overwhelmed the seperator's capability.

Water is bad news for air tools, and wooden projects that have a finely sanded surface.

For this reason, I'd recommend the largest tank you can afford.

ooc
 
Note about Campbell Hausfield......

I believe both of the compressors I've had are Campbell Hausfield, and pics of them can be seen in my shop photos.

The two stage cast iron 80gal is rated at 7hp peak, and probably is one of the overated ones Bill mentioned in his post. It is likely to be less. Home Depot states it is 4hp......but, whatever it is, it's very much an improvement over the 2hp 20gal that I used to have.

Campbell Hausfield is a good name, and I've been very happy with the quality and performance of the two I've had.

ooc
 
allen jay said:
the important part to look for on the label Is what the "SCFM" RATING IS "sustained cubic feet per minute" basically the constant flow of air while the compressor is running at a given pressure 12 scfm @ 90 psi ( as an example)
it is always different than the cfm rating. when you go to purchase air tools, look at the label on the tool for the scfm rating required, if your compressor wont give you that output then your compressor is too small and the tool requires more air than your compressor can supply to make it operate properly.
this is especially important if you are using air sanders or air files that consume alot of air in a short amount of time.
and to offer an opinion in size i would get atleast a 60 gallon tank.
not sure how the 2 stage thing came up but you will pay dearly for a 2 stage unit
Click to expand...

Allen,

Not to be picky, but SCFM is "standard" CFM which is slightly different from CFM or ACFM. Here's a website that explains the difference and shows how to convert one rating to the other.

http://www.ehow.com/how_6156309_convert-scfm-cfm.html
 
Ooops

John King said:
Mark - My data is correct.

Campbell Hausfeld VT6290 = twin cylinder oil lubricated pump, 20 gallon tank, 2 running horsepower, 120 volt, 15 amp. I never said anything about 2-stage pump. - John
Click to expand...

Morning John,

Looked up your model number. Depending on what you will be using it for, that compressor may not be ideal. Rated at less than 6 SCFM at 90psi, you may run into problems if you plan on doing spray finishing or use air tools. You can get a lot more compressor for the same money. See John's link in his response.
 
Mark Mandell said:
Morning John,

Looked up your model number. Depending on what you will be using it for, that compressor may not be ideal. Rated at less than 6 SCFM at 90psi, you may run into problems if you plan on doing spray finishing or use air tools. You can get a lot more compressor for the same money. See John's link in his response.
Click to expand...

Spraying with a smaller HVLP guns (a minijet is 4cfm at 29psi) , the CFMs on this would be ok, the problem is the tank will empty fairly quick. 20 Gallons is a small tank.
Air sanding and grinders would use about 10cfm at 90+ psi and the duty cycle of the compressor would probably not work in that application.

Look at it as air out of the tank will flow as fast as the line size, valves etc will allow. So a smaller tank will need to be refilled. The other issue is how high it will store the air. If it cuts off at 100 PSI, there isn't as much in the tank as if it cut off at 150psi. How long it takes to refill the tank is the question on a smaller compressor.
With a storage tank at 100 PSI, assuming constant pressure, in a 3/8" hose (id), you can flow 20+ CFM. You can use this rate calculator from Rapidair products (good stuff to)
http://rapidairproducts.com/flowrate.asp


With a compressor, bigger is most always better. If you have the money for a 60 or 80 gallon tank and a 220V 3-5hp, that would be the way to go. If you don't then you have to make the compromises necessary to the budget and space.

With me, it was about space and noise. I bought a Belaire QP, but it is not cheap, but when it is running in my 2 car shop, I can still hear the radio and don't need muffs.
http://www.belairecompressors.com/p_qp-quiet-performance.html
 
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compressor

I have a small pancake porter cable compressor and it worked for a year and now it won't hold pressure and am having trouble finding out just what the probolem is. I also have a 30 gallon one that holds pressure much longer and I would choose it over the pancake. Mowst of my work is done in the shop and I find longer pressure is better and it starting and stoppiing.
 
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