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Air compressor

Post in 'DIY and General non-hearth advice' started by mayhem, Jul 22, 2009.

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  1. mayhem

    mayhem Minister of Fire

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    Thinking about getting a homeowner grade air compressor and need some advice. Not looking to blow (no pun intended) alot of money on it, but I'd rather spend a few extra bucks and get the right product than spend less and not have it be useful. please note this will not be used for commercial purposes, it won't be used daily and proabbly not even weekly. It'll be used when I need it for a project or small job and then put away in the corner of my basement till I ned it again.

    I want a basic compressor for regular around the house things like inflating tires (ranging from my daughter's bike to my Sliverado), kids inflatable toys (baksetball, a swimming pool) up to DIY and weekend warrior work...blowing out my saw or an air filter, running a nailgun to do framing for room walls or a shed project...an ideal would be to also have something that can run automotive tools like an air ratchet or impact driver, air chisel, and a sanding/grinding wheel...but those requirements may be putting me out of my budget...I don't need to run a paint gun, which I'm guess is proabbly the highest air volume tool since you probably need alot of air and a consistent pressure. I know there is a big difference in the air volume required for a nailgun and an air ratchet or a grinder...the question is wether a simple compressor will run one in a meaningful way or if it just wouldn't provide enough pressure to make the impact gun a useful tool.

    The oil free units I've heard are nice because they're low maintenance, but also that they're disposable and once you have trouble you might as well go shopping for a new compressor. Oiled compressors I've heard tend to last much longer, provided you actually do oil them of course, which I don't think is a big deal.

    Is condensation an issue in these things or do they all pretty mcuh dehumidify the air they use? Don't want to rot it from the inside out from low usage, do I jsut drain the tank when it snot in use/ It will not be left plugged in except when its in use.

    What do the specs mean to me? I gather that the higher the pressure the more versatility i get out of it in that I can use more powerful tools at 125psi than at 40 psi and that the tank size equates to longer runtimes between power cycles on the motor, which means less noise while I'm working since I think these thigns tend to be pretty loud.

    I see a bunch of low to medium duty compressors on Sears' website that fit my budget...wondering if they'll do the trick or if they're too small. Links below.

    Other than it doesn't have wheels for portability (though it does have a handle so its proabbly not too excessive to move it around), this one would be great...comes with a basic tool set and the accessory list shows tools like air ratchts and impact guns...but is it strong enough to really make those tools worthwhile? The price is very right for my budget. If this one will do what I'm looking for then I'll go grab it today.

    http://www.sears.com/shc/s/p_10153_...Compressors & Air Tools&sName=Air Compressors

    Nice one. Big wheels, double the size tank, looks like the same motor though, so I'm guess its really not significantly more capable of running tools than the little one, it just works the motor less. This is on the outside of my budget right now.

    http://www.sears.com/shc/s/p_10153_...Compressors & Air Tools&sName=Air Compressors

    Thanks!

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  2. d.n.f.

    d.n.f. New Member

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    I am on my 2nd air compressor. Using it for all the stuff you are (no painting), but I do run air tools (grinders) and to blow out hose lines.
    First one I bought (oil less) was cheap and junk. Didn't know better.
    Second oil less one I bought had a good name but it screams.
    My friend has an oily model and it churns at a low rpm all day. Mine just makes tons of noise and makes tons of heat (which leads me to believe the motor will not last).

    My next buy when this one dies will be an oiled model.
  3. stee6043

    stee6043 Minister of Fire

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    I've had a very good experience with my consumer grade Craftsman compressor. I use it for a lot of things, not the least of which is blowing out my under ground sprinklers each Fall. For something most of us use so infrequently I have a hard time recommending anything higher end than a Sears unit.

    The commercial guys need compressors like Kaeser, Quincy, IR, Sulair, etc. But for home use I think you'll be fine with a Sears...

    Here is the unit I'm running. Very pleased...

    http://www.sears.com/shc/s/p_10153_...Compressors & Air Tools&sName=Air Compressors
  4. mayhem

    mayhem Minister of Fire

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    What size tank and motor do you have? Do you happen to know the same info for your friend's compressor?
  5. SolarAndWood

    SolarAndWood Minister of Fire

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    I have the Bostich pancake compressor they sell at Lowes, think it is a 2hp. Works fine for the framing nailer and all the other things you mentioned. The only time I have found it doesn't keep up is if I'm roofing and have a couple guys feeding me shingles or sheathing and all I am doing is shooting nails. It takes a lot of coordination to have that happen and would probably never happen to the weekend warrior.
  6. pybyr

    pybyr Minister of Fire

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    I bought a compressor aiming to do (and have successfully used it to do) all the sorts of stuff that you mention-- it's this one, and I've been very happy with it:

    http://www.deltaportercable.com/Products/ProductDetail.aspx?ProductID=13643

    I've successfully used it to power a 1/2 inch impact wrench-- the only limiting factor is that if you run the wrench frequently or for a long spell (actually a real long while considering how fast air wrenches get the work done), the pressure will eventually start to drop and you have to pause (for maybe 15 seconds at most to let the compressor fill the tanks back up to full pressure. I've even used it with success to run a small paint sprayer- and it yielded thoroughly decent results (though not pro-finish results).

    Regarding draining of moisture from the tank-- a very good idea with whatever you get-- you'll be surprised how much water you mat get. Simply open the drain petcock on the bottom and let the moisture out after you finish using it for a task, before you put it away.
  7. lobsta1

    lobsta1 Member

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  8. SolarAndWood

    SolarAndWood Minister of Fire

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    Very true Al. The pancakes advantage is portability and you can store them on a shelf. Mayhem, the only issue I see with the two links you have is the pressure. If you are shooting 16s with a framing nailer into dense material, you will be close to the design pressure. Maybe with the bigger tank, it won't be an issue but there are plenty of inexpensive 150 psi compressors out there.
  9. mayhem

    mayhem Minister of Fire

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    I think I'm probably going to hold off for now. My needs are not immediate so its better if I save some extra cash to get the right compressor. I can get the oil-lubed 150psi 20-33 gallon Craftsman models for under $300 and they'll do everything I might need.

    Thansk one and all!
  10. d.n.f.

    d.n.f. New Member

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    His is a Bostich two tanker. Very portable. Weighs about ten pounds more than my portable two tanker. He uses his every day for woodworking and nailing. Had it ten plus years.
    No idea about the hp or max air pressure (cfm?).
  11. Sting

    Sting Feeling the Heat

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    once you figure out the CFM that you need to do your work

    Look at two things - That or greater CFM and the slowest compressor RPM that will make that CFM -That you can find or afford
  12. kbjelka

    kbjelka New Member

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    I agree with sting CFM delivery should be your main concern.

    I bought the Craftsman Professional 25 gal. Air Compressor, 1.8 hp, Horizontal Tank after years of holding off for the right model. It's got enough CFM delivery to handle pretty much anything. It's quiet and it will most likely be in my two year old sons garage thirty years from now. It's a bit on they pricey side but my landscaper buddy has had a few oil less models and has had nothing but problems. If you cheap out and or get a low CFM model I think you will regret it.

    http://www.sears.com/shc/s/p_10153_12605_00919541000P?keyword=craftsman professional air compressor

    Here's a review of this model posted by a sears technician which is pretty telling..

    "I am a Sears Repair Technician with almost 40 years of experience, , and in the last 10 years, I can't remember more than one or two of these units entering our shop, (even then it was a minor thing), I have one that is over 20 years old and it is still working fine. Air leaks happen on any brand, and you just have to find them and tighten up a fitting or two. This is a great unit, it almost never breaks down, and it has the power to recover quickly. If you want a reliable air compressor, buy this one. You'll never need another one. I would recommend this unit above all competition."
  13. Gooserider

    Gooserider Mod Emeritus

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    The big numbers to worry about are Air Consumption / Production rate, which will be measured in CFM / @ pressure - i.e. 3cfm@90psi, and working pressure. Tank size is also an issue, but less of one.

    If you intend to use a tool constantly, you need to have a compressor that puts out more CFM than the tool requires. If you do this, then your tool will run at full power all the time, with the compressor cycling as needed to maintain the tank pressure. You must also have a working pressure greater than the tool requires. Most tools require a pressure around 90psi, with paint guns needing around 40. Avoid running the tool at higher than it's listed working pressure, as this can damage it... Running a tool at less than rated pressure won't usually hurt it, but most will run out of power if the pressure drops to low. If the compressor is too much smaller than the tool, you really won't be able to get any work done. If it is slightly smaller, then your work becomes episodic, as you work for a moment or two until you run out of pressure, wait for the compressor to build back up, work some more, etc. This gets really frustrating after a while...

    Most tools will list their nominally designed pressure / volume specs - commonly 4-5cfm @ 90psi for "garage tools", 1-2cfm @ 90psi for nailers, etc. Your compressor will usually give you the rated cfm output at several pressures - typically 40psi, 90psi, and whatever the units maximum pressure is.

    As you suspected, the tank size has a lot to do with the frequency with which the compressor cycles - the larger the tank and the higher the pressure it cycles to, the longer you can run on the tank without the compressor motor kicking in. "pancake" style units sacrifice this in the name of portability, you are better off getting the largest tank you can deal with, especially if the compressor won't be moved around much.

    EVERYBODY seems to lie about CFM ratings - the compressor makers claim the compressors make more volume than they do, and the tool makers claim their tools pull less volume - you will do better if you figure the actual output of the compressor will be half what's claimed, and that tools take twice whats claimed.

    Oil-less units produce (in theory) cleaner air - oil units get a certain minimal amount of blowby from the rings, and are easier to transport since they don't mind tipping, are lighter, and can be operated in odd positions (i.e. sitting on a roof) Downside is that they tend to be lower capacity, much noisier in operation, and have shorter life-spans. Oil units have crankcases just like an engine, and need to be filled / checked / changed just like any small engine - actually there is no major mechanical difference between an engine and a compressor. They are a bit heavier, harder to transport (don't tip) must be operated in close to normal level position, and may put small amounts of oil mist into the air lines. However they are quieter, and last longer. Maintainance is not a big deal - my compressor is several years old, the oil still looks like new, and has never needed any added to it.

    If one is doing painting, an oil-less unit is arguably better, although you should do some serious filtration on any compressor to ensure that your air is dry and clean in order to keep the paint from being affected, so it isn't a big issue.

    I have two compressors, one is a 20 gallon, horizontal tank, 3hp Quincy, oil unit - I would consider it the minimal unit for use w/ garage type air-tools - It will barely keep up with intermittent use tools like air ratchets and impact guns, and does fine with my little "pencil type" die grinder, but if using a larger die grinder or a whiz-wheel cutter, it runs out of steam after about a minute of use, then needs 2-3 minutes to pump back up again - VERY frustrating. But the specs on it say that it SHOULD have about the same output as the tools I'm using require - I purchased it assuming the specs were honest all the way around, but if I had it to do over again, I would have gone for a bigger unit.

    The second compressor is a little Campbell/Hausefield oil-less pancake that I inherited from my father - it is OK with a nail gun, inflating tires, or for a blower, but I would not even try to use it with an air ratchet or impact gun as it would probably only supply a few seconds of working power per cycle. It is handy for occasional jobs that need a portable air supply, but I could easily live without it.

    Note that kids toys / inflateables mostly do NOT work well with a compressor - they usually need a low pressure / high volume pump, the opposite of most compressors - you can get cheap electric or manual pumps for this that work great - using a compressor you have a serious risk of over inflating them, w/ resulting explosion...

    If I had it to do over, I would look at one of the 40-60 gallon upright tank units with a ~5hp electric motor and at least a 6-7cfm @ 90psi output spec, and a 125-150psi tank pressure rating. That would allow me to use any of my air tools w/o having to constantly stop and let the compressor build back up... I have seen this configuration fairly often for $4-600 or so... I would NOT go to Sears - they don't make their compressors, (or anything else) they just slap their name on a low-bid built product from somebody else.... You can get better prices from other places such as Northern or HF, and probably about the same quality...

    Gooserider
  14. Sting

    Sting Feeling the Heat

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    HP ratings are often grossly misrepresented just to sell product -- humm sounds like another product dear to us hu???

    It takes 8.8 amps @115 volts or 4.4 amps @230 volts to equal one horse-power. Make sure your comparing units rated by amp draw not advertised horse power

    Advertised horse power and tank size will jade folks just like sparkles on donuts will hide the true product your buying -- or more important = wanting to buy but are being mislead down the yellow brick road.

    Buy CFM not HP

    lots of good information here http://castair.net/ too far away to effect your purchase - just information
  15. Metal

    Metal Minister of Fire

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    I've had this one:
    http://www.sears.com/shc/s/p_10153_...Compressors & Air Tools&sName=Air Compressors
    for about three years and have used it for everything from blowing out my irrigation system to rotating tires with the impact wrench (it was on sale for ~$279) and it has worked flawlessly. It is a bit noisy, but you should probably wear hearing protection anyway if you are using the tools that make it kick on a lot (nailers, impact wrenches, etc.), and with that much volume it doesn't have to kick on very often. The only issue would be getting it up and down stairs : )
  16. 'bert

    'bert Minister of Fire

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    I would not worry to much about portability, find a place to put it and buy some additional air hose (it's cheap at Costco). That way you can consider bigger units and still be able you use them anywhere around the yard.

    I have the typical 60 gal / 7 hp vertical type and still find that it runs out of air with some tools. Die grinders will take as much air as you can throw at them.

    Easier to put some extra air hose on the shelf then a frustratingly small compressor.
  17. dgold

    dgold New Member

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    In the interest of full disclosure, let me say up front that I have skin in this game. I don't wish to name my employer, but I'm very familiar with air compressors. There are a lot of common misconceptions when it comes to air compressors. Hopefully the following will help.

    As specs go, too much emphasis is put on CFM specs in my opinion. Here's why:

    1. Tools rated at 5 cfm (like an impact wrench - a very useful, and relatively inexpensive tool) actually draw 20-25 CFM. If you look closely they're all rated "average" cfm, which typically assumes a 20% or 25% duty cycle. No compressor pump any of us are going to buy can keep up with that volume of air consumption.

    2. CFM is typically rated at 40 or 90 psi, which totally ignores the phenomenon of pressure drop. If you're pump is delivering 90 psi, the only time your tool sees 90 psi is when it's not being used. Pull the trigger and the pressure at the tool is 30-50 PSI less -- hook up a plumbing tee with a pressure gauge at the tool and see for yourself. This is why most auto mechanics shops have their regulators turned up way higher. Their tools don't operate properly when the regulators are set to 90psi.

    My point is, the conventional wisdom that a 5 CFM @ 90 PSI compressor can continuously run a "3 CFM" tool is inacurate, since the 3 CFM tool probably pulls 15 CFM, and it really needs it at at least 120 psi at the compressor end of the system. The only distributor that details this accurately (that I'm aware of) is Grainger - they give you both "average" and actual air flow ratings for most of the tools.

    CFM is a good indicator (albeit directional only) of how long it'll take the pump to fill the tank, or recover from use after you've drained some of the air out. Problem is, CFM @ 90 psi doesn't mean much when you're filling the tank up to 150 psi after you've emptied it down to 120 psi. (As PSI increases, CFM delivery decreases - especially with single stage pumps.)

    As far as how well it'll run an air tool, do this equation:
    Gallons x (max storage psi - 120 psi) = reserve coefficient (in psi-gallons)

    It won't tell you how long the tool will run, but it will help you compare the value of two compressors side by side. If the reserve of compressor A is 2x that of compresor B, than compressor A should be able to run your tool - while maintaining 90 psi at the tool - roughly twice as long. Why subtract 120 psi in the equation above? Pressure drop. Once the tank falls below 120 psi, the compressor can't realistically deliver 90 psi at the tool while running. This is why a compressor that stores air at 150psi will deliver about twice the runtime as a compressor that stores air at 135 psi -- assuming tank size is equal. You can do this equation for 40 psi spray guns too, but instead of subtracting 120 psi, maybe only subtract 70 psi)

    What you'll find is that reserve (tank) pressure makes a HUGE difference in tool performance. I agree that many of the pancakes are extremely noisy, but don't assume they're noisy because they're oil free. If you look around, there are some relatively quiet oil-free compressors out there -- and very long lasting too. Like most things, you tend to get what you pay for, whether oil lube or oil free. If someone can build an oil-lube, cast iron compressor pump for the same price as an oil-free compressor, they're cutting a corner somewhere - more parts, more machining, seals, gaskets, etc all cost money.

    Other things that make a huge difference: shorter hoses, larger diameter hoses, and high quality quick-connects. Don't buy the el-cheapo quick connects, buy the good ones for a few dollars more. They're much less restrictive and help reduce pressure drop -- which makes a huge difference.

    Lastly, as someone else wrote, HP ratings are often overstated. Look for the phrase "running horsepower". This number should be fairly accurate.
  18. Later

    Later New Member

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    Great answer! I now understand what all the numbers mean. Thanks
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