Help me pick an air compressor!

[JustinOlson]

I've been looking at Air Compressors for a while at various stores. From what I've found out, I want an air compressor that is dual stage. I'm leaning towards a 80 gallon twin stage compressor capable of 175 psi. This should help me maintain good CFM at higher pressures while not constantly running due to lack of capacity. Beyond that, what should I look out for when choosing a compressor for my shop? What brands are good?

 

 

What do you guys think about this one?

 

http://portercable.cpoworkshop.com/compressors/c7550.html?ref=yahooc7550

 

 

Regards,

Justin

[91_4x4runner]

That's one hell of an air compressor. You're talking some serious $$$. Here's what I've settled on:

 

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200311707_200311707

 

Fulfills the requirements of most air tools I'll ever run. It comes with a 2 year parts and labor warranty, which ought to be long enough to prove worthiness.

 

What type of tools are you going to be running?

[Cruez]

When I bought my first one.. It was a 60 gallon 10.4 CFM unit... It is okay with everything but extended use with a die grinder or DA. Sand blasting is 5 minutes at a time.

 

I upgraded to a 80 gallon 19.5 CFM unit and it works very well... The only problem I have now is that I have upped the pressure on my blaster since it can produce more and it will run out of air at 120 psi @ 21 CFM in about 5-10 minutes..

 

Moral of the story... get the biggest one you can afford if you plan on using it a lot.

[240zV8]

Bigger is definently better, 80 gallon + with like 18+cfm would be my reccomendation

[Brad-ManQ45]

Hey Justin:

 

What all do you anticipate using it for?

 

I have heard that Bel Aire makes good ones.

 

I myself have a CH single stage 125 that I bought for $400. I have a blast cabinet and a pressure blaster and haven't run out of air before I was finished with anything yet - but then I haven't used my DA yet.

 

Since I have an HVLP gun, I'll have no problem with that either.

 

I believe it was Grumpy that suggested getting two single stage 60 Gal. instead of one 80 Gal 2 stage - but then ther is a bit more room and wiring to deal with, but you wind up with more CFM and tank capacity than the single 2 stage.

 

The difference in cost would mre than pay for wiring....

 

I have one of the 30 gal oiless compressors that I have already made provision to plumb in if I need more volume - but that is something I have had for about twice as long as the big compressor, and is convenient for some portable air needs.

[grumpyvette]

most shops have or would like to have an air compressor to run air wrenchs, fill tires, run die grinders ETC. the problem, is most reasonably priced air compressors can,t maintain the flow voluum at reasonable pressure levels and your constantly waiting for the tank to re-pressurize so you can use the air tools for more than a few minutes at a time, cheap compressors lack the tank size and flow to keep up, and few guys have the room or want to spend several thousand dollars on a commercial compressor, which can easily cost twice too three times what two home shop,compressors cost , (just try priceing a 15hp 160 gallon compressor that will duplicate what the two compressors can do)

 

yeah, the use of TWO of the cheaper 60-80 gallon single stage compressors feeding a single comon air pipe with taps around the shop is usually far cheaper than trying to find a decent single compressor that will keep up with most tool demand, keep in mind pressures above about 125 psi are not usually needed or necessary but having the voluum of air flow two seperate compressors can provide is usually a big plus. just try priceing a 15hp/160 gallon compressor (the same as two smaller copmpressors)

BTW I got my current compressors at HOME DEPOT for $450 each, rated at 7hp 80 gallon, 130 psi

 

similar to this, but I don,t currently see the exact one listed

 

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100349429

 

btw

I used several hundered feet of 3/4" schedual 80 PVC pipe rated at 660 PSI to pipe the air around the shop and used brass fittings screwed and glued into the pick-up access points , both compressors feed a 3/4" pipe that then dips to a drain valve then shoots over the rafters to a (T) where its routed along the walls to every place I might EVER use air flow to clean or opperate tools in the shop,and its worked flawlessly at about 1/8 the price of copper pipe and sweated joints I used in the previous shop.

keep in mind moisture tends to run down hill so route your pipes so that the pipes drain to drain valve locations and all access points to draw air are higher than the drain points IE don,t run the pipe level with the floor,pick-up points should be higher than drains and there should be several drain valve points, one near the compressors and at least one more before any access to the air for tools my compressors are feeding the pipe at 5 feet from the floor,it slants to a drain at 4.9 ft from the floor,then shoots dirrectly up the wall,over the rafters in a sweeping curve and drops to the opposite side of the shop at a drain at 5 ft from the floor, all access points are tees 6 ft from the floor

 

yes IM aware that PVC pipe is not generally suggested for pressurized air....and sweated copper or galvanized steel is suggested...

 

Oh IM only too aware of the minimal risks, but Im also aware of the huge cost differance, like 800% higher for copper and steel pipe rusts,, the copper pipe I used in the last shop would have cost me hundreds of dollars in this shop,the better moisture tollerance and several hundred psi safety margin (pipes rated at 660 psi and it will never see 140 psi) and almost negligible risk of injury, the worst case is it fails too hold air pressure and my air tools don,t work

I probably would never have tried it if a buddys shop had not used it without any problems for over 12 years now , and hes located less than 5 miles from here so he gets similar shop temps and pressures on the pipe,

[G.I.jonas]

That porter cable is just what i have and i would recommend anyday.

[Metallicar]

BTW I got my current compressors at HOME DEPOT for $450 each, rated at 7hp 80 gallon, 130 psi

 

Those huge compressors at Home Depot sit in the store for a long time. I recommend going right to the Store General Manager, and ask him to drop the price if you have cash in hand. I picked one up for 20% less than Grumpyvette. A 10% discount is easy to get anyday from HD, ask for 20% on a big ticket, slow seller and you can get it!

[Tony D]

yes IM aware that PVC pipe is not generally suggested for pressurized air....

Oh IM only too aware of the minimal risks, but Im also aware of the huge cost differance, I probably would never have tried it if a buddys shop had not used it without any problems for over 12 years now , and hes located less than 5 miles from here so he gets similar shop temps and pressures on the pipe,

 

PLEASE! Tell me that both you and your friend are using good old ND 30 compressor oil in your units, and DO NOT use Synthetic!

 

PAO or PAG based Synthetic Compressor Oils WILL attack any of the polycarbonate or polyvinylchloride plastics used in piping and separator bowls.

 

Ever wonder why the Polycarbonate Bowls have a metal cage around them? When synthetic oil gets onto the plastic it weakens it without much outward signs at all---and then catastrophically goes BOOM!

 

I personally have been in the area when a bowl has let go. Luckily nobody was around to get hit by the flying shards.

 

I have responded to customers with PVC systems at the request of Hartford Steam Boiler Company for insurance estimations of replacements after large runs (like you said, water...and oil...runs downhill) of piping in horizontal or near horizontal positions have catastrophically and without warning split or blown apart.

 

This is DIRECTLY caused by SYNTHETIC OILS. If you are running PVC or ANY kind of plastic piping DO NOT RUN SYNTHETIC OIL IN YOUR COMPRESSOR!!!

 

Also, make sure you have GOOOOOOD aerosol and condensate removing filters at the compressor.

 

If I have a customer that wants to save money by using plastic pipe, I will insist on copper or stainless steel piping from the compressor to the Wet Receiver, and from there to the Dryer into the Dry Receiver. From that point, most everything is knocked out, and IMO the risk is minimal. For a smaller system I'd run stainless or copper to the last stage of separation, and go plastic from there.

 

I have seen PVC droop from heat, balloon up from discharge heat, split, fracture, explode, and otherwise do some very nasty things dealing with compressed air. If you use it, try to separate out as much of the oil aerosols that you can as near the compressor as you can to minimize risk.

 

BTW, in one case, the pipes were in for 10 years before there was a problem. They had been using Synthetic for a year at that point, due to maintenance costs on the screw compressors they were using being greatly reduced using synthetic oils.

 

For a small recip, stick with standard ND 30 Compressor Oil, if you use Synthetic and plastic, there is a good chance something can happen. Been there, seen that!

 

On to Tank Size: The larger tank you have, the less horsepower you need. In theory if you have a lagre enough tank to handle you peak loads you can get by with one of those 12V tire compressors! Tank capacity is good for two reasons: Residence Time, and Recovery Time. Bigger tanks have more 'residence time' for the air, meaning it can sit there and cool---this means condensate forms in the TANK for the most part, and not in your lines. Residence time means debris in the airstream has time to settle out--by debris it can mean oil residues and oil aerosols as well. Small droplets fall as gravity work on them---smaller tanks have a flow through them and can carry this out into the lines---a good reason for putting a coalescer on right after the outlet valve on the tank.

 

Recovery time is the time it takes to come back up to pressure. Almost universally people who increase the tank size do not readjust their pressure switch accordingly. This is not just homeowners---this goes for people with 6, 500HP Dry Screw Units and several thousand gallons of storage capacity as well! What a larger reservoir does for you is of course increase storage. To take advantage of this, you should decrease the cut in/cut out differential on your compressors. Many times you can't do this with the switch that comes on most of the cheapie home units. I use relay controls and an Allen Bradley 745 Series switch from Grainger. It has both adjustable cut out and differential. Running two 300 gallon tanks, I run a 2 psi Differential on the compressor. Normally this would have the compressor running on and off with only an 80 gallon tank. But it takes 3 minutes for me to bring tank pressure up 2psi---about the same time it took the same compressor to bring it up from 90psi to 120 when on the 80 gallon tank alone.

 

What this does is keep your compressor operating at peak efficiency (full load) and decreases system pressure variations. It's a pain when the tank is at 90psi, and the nail gun is not sinking the 3"r's all the way in! With the compressor differential being set to 2 psi, it keeps pressure constant, and doesn't really result in the compressor running any longer that otherwise.

 

This is why you regulate down to system pressure, and then regulate down again at hose connecct at point of use. You will find your end-point pressure stays much more constant when you set it up this way, but it will take a $75 dollar switch retrofit, and maybe some relays. Grunmpyvette is correct, however you reach the pressure or flow rate is really irrelevant---you can run two or three units into a common receiver. But jsut remember that you store pressure at higher pressure, and regulate down at least twice to point of use.

 

Run your storage tank at whatever the compressor is rated at, your lines to the shop (regulated at the tank) at 100psi, and then the point of use with proper lines to final pressure: 30 to 90psi usually.

 

Also, making a 'ring' configuration will cut piping losses in half as any point in the system can be fed from two pipes---similar to his two into one setup.

 

Scrounge around Portland area, there are several large compressor manufacturers in your area (Rogers Machinery, Burton Compressor, I-R Air Center comes to mind) and see if they have some old tanks they took in on trade they are looking to unload or sell cheaply. Many times you can get a KILLER deal on a 7HP 3-Phase industrial unit that will last you for a lifetime, all your cost is in replacing the motor with a single phase motor. That is probably the largest size most homes can handle with the wiring available---that will be 7 to 14 Amps 220V. If you can scrounge the tanks, you can set up a really nice ssytem with plenty of storage and separation. Just remember to put ball valves at each tank inlet and outlet so you can shut them off individually, and hold pressure in between the times you use it. Makes it nice when you want to fill up a tire or two, or even blow off some stuff and you don't need to start the compressor....just open the valve do your thing and cork it back up for storage.

 

Air Stores Well!

[Tony D]

On another note, Graniger also sells 'Alternator Boxes' for compressors....if you take the pressure switching off the compressors themselves and put it remotely, with two compressors you can set up a 'lead-lag' setup.

Basically, below say 125psi, both compressors run on their respective starters or contactors. At 125, one compressor shuts off, and the other 'the lead' will pump up to final pressure 135, 150, 175 whatever. At that point, when it shuts off after reaching pressure...the alternator box will switch the compressors 'lead-lag' relationship, so that when the pressure switch calls for it to load again, the other compressor kicks on the supply demand.

 

If at any time the pressure drops below the lead cutout the second compressor will also kick back on, and maintain the pressure.

 

This setup really increases the life of recips, and keeps them cooler overall. This is one good reason to have compressors rated at least 10% above line pressure requirements (say 100psi line, 110psi for storage, and 120-125 for lead cutout).

 

There is a rule that you should only compress to the pressure you need, and nothing more---but this is for industrial rated units that can operate at 100% load all the time. The compressors being discussed here are not in that catagory. I'm talking a Quincy QRD style unit---that pump alone costs $5000! Some others come to mind, but when you get into that kind of money, the new lower-cost Atlas Copco GX screw units with integrated Oil Separator and Dryer start to make more sense. And now, finally after 20 years of people begging for them to do so, they FINALLY have a screw unit in the 2 to 7 HP range that is SINGLE PHASE.

 

If you want a compressor that will run 100% of the time, supply clean, oil separated air, and be quieter than most refrigerators, take a look at the Atlas Copco GX units (even though they are a competitor to the company I currently work for!) they really are Cadillac Compressors. (Maybe Stripped down to Buick or Olds configuration, but still a fine quality unit!)

 

I see right now one of these is on e-bay (15HP) selling for around $4K...

Brochure here:

http://www.benzcas.com/atlas-copco/pdfs/gx-2-22.pdf

 

E-Bay Auction Here:

http://cgi.ebay.com/Atlas-Copco-Model-GX5-150-FF-AIR-COMPRESSOR_W0QQitemZ180144707910QQihZ008QQcategoryZ106436QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Chances are good your local Atlas Copco Dealer will have one in stock close to that price...maybe maybe not... See what happens on the sale. If it was closer, I'd consider it... Nah, I'd get one as a 'take off' from a compressor retrofit. LOL

[Evan Purple240zt]

I had a body shop for a year or so. We cooked a used porter-cable. Not the compressors fault I am sure. Musta been something else.

 

I ended up dropping 3300 on a snapon unit. Big red was the maker. I had good luck but the atlas mentioned sounds really nice and quiet.

 

I also worked in a car audio shop with a good sized puma unit, was fine for what we did. We almost killed it too. I had a porter cable at tweeter. Funny thing, at both jobs I was the ONLY one who maintained them EVER. Nobody bled tanks or changed crankcase oil.

 

Blew a line in the middle of the night and the compressor ran straight for 12 hours or so. I thought it was dead, it smelled like it had burnt up totally.

 

I have no real useful info, but just wanted to tell you to turn off the compressor when not in use! Protect your investment.

 

Evan

[2003z]

www.eatoncompressor.com

my 5hp 60gallon will out perform any home depot 7.5hp 80 gallon any day. Its motor runs at half speed and is a true 5hp. It actually cycles on and off while I sandblast and I run it for several hours per day.

[Pop N Wood]

That Porter Cable should do everything a guy in a home shop could want. 30 amps at 240V. That is a big mofo. Maybe you won't be sandblasting aircraft carriers with it but it would sure do me proud.

 

I have a rated 5 HP unit wired to a 20 amp 240V outlet (so it can't be a true 5 HP continusous). It will run continuously with continued grinder usage, but I have never had to stop to wait for it.

 

And I am a little suprised about Grumpy using PVC in his air supply. Check out the OSHA web site about using PVC for compressed gasses.

 

I don't feel so inadequate about my low buck shop crane anymore.

[grumpyvette]

I took ALOT of crap on iother sites after posting this .....

 

 

Oh IM only too aware of the minimal risks, but Im also aware of the huge cost differance, like 800% higher for copper and steel pipe rusts,, the copper pipe I used in the last shop would have cost me hundreds of dollars in this shop,the better moisture tollerance and several hundred psi safety margin (pipes rated at 660 psi and it will never see 140 psi) and almost negligible risk of injury, the worst case is it fails too hold air pressure and my air tools don,t work

I probably would never have tried it if a buddys shop had not used it without any problems for over 12 years now , and hes located less than 5 miles from here so he gets similar shop temps and pressures on the pipe,

IF.. I ever have the slightest problem ...Ill yank it out in a heart beat, and replace it with 3/4" hard copper pipe, sweated fittings like my old shop, but its been in use now for over a year in my garage, and over 12 years in a buddys garage with no problems, I just don,t see it as a potential flaw as of yet.

 

personally I think all these dire warnings and predictions of impending doom are based on guys in the past useing cheap scedule 40 PVC ,and most likely connected where heat and vibration influenced the results, Ive used SCHEDULE 80 and its all mounted where its not ever going to be hit and firmly clamped to a concrete wall and rafters and its rated at 690 PSI, thats a 500% safety margin ,theres standard hydrolic hose from the compressors to the input point and theres a shut-off valve on each compressor. yeah IM aware that at 110 degrees F its down to a 300% safety margin , but since my compressors combined flow/pressure rarely reaches 120psi, I don,t feel all that threatened, if an when I have a problem ILL change it out, but its seems like a tempest in a tea pot problem at this point!

 

http://www.harvel.com/tech-specs-pvc-pipe-40.asp

 

theres a differance

 

http://www.harvel.com/tech-specs-pvc-pipe-80.asp

 

LIKE I said before, if it fails I see the air tools not working and little else being effected untill it gets replaced

[getZ]

You can always run an another regulator to the pipes. My compressor will charge up to 175psi, but my lines never see over a 100 psi.

 

I was planning on running a line to the side of my house over the attic just using regular compressor hose. The funky orange home depot ones I have are about ten years old with no signs of aging. Its about 20 bucks for a 50 foot hose. They are rated to 300 psi. If you want it to look pretty, tack it on to a strip of wood every foot or so. Easy enough to replace every ten years.

 

As far as compressors go, I like my Ingersol Rand. You can get them pretty reasonable and direct shipped though Northern tools: http://www.northerntool.com/webapp/wcs/stores/servlet/category_6970_87