10

Many times I've struggled with stubborn bolts, cursing car manufacturers wth a number of expletives in languages I didn't know I could speak. Stripped, rusted, or fused, these bolts can make any breaker bar retire early and hit happy hour. Unfortunately if I ever wanted to mod any of my cars, my only other option was blowing off some steam… well, hot air really. My air compressor is not only convenient, but necessary.

Compressors come in many shapes and sizes. Most of the larger compressors can run longer, more efficiently, and have tanks to store the compressed air for maximum use. Compact air compressors don't usually have storage tanks and must run continuously to provide an adequate air supply. They are good for small jobs, anything from refilling tires to blowing up inflatable dolls, right Kojima? ;)

Ingersoll Rand air compressor
This is like the grand daddy of air compressors.  It's a two stage, two cylinder splash lubricated belt-driven (dirty talk, I know!) air compressor with 14 horsepower and pushes 25cfm at 175psi (seriously!).  You'll have to cough up a few g's to own this baby.

Air compressors convert electric energy into kinetic energy. Some use rotating impellers to generate air pressure. Most use a reciprocating piston to increase air pressure by reducing the size of the space where the air is contained. A conventional piston compressor uses a crankshaft driven by an electric motor or gas engine as well as a connecting rod, piston, cylinder and valve head. The valve head contains the inlet and discharge valves. Air enters the inlet valve and fills the space above the piston. When the piston moves up, it compresses the air, which exits through the discharge valve into the tank or an air hose. 

Single Stage versus Two Stage
A single stage compressor has one piston that compresses and transports air to the tank. It can be a single or multi cylinder compressor. Single stage compressors are usually good for air pressures up to 150 psi. Two stage compressors are usually used for continuous or heavy duty use or if maximum ratings above 150 psi are necessary. One piston compresses the air and delivers it past a check valve where it is cooled. A second piston compresses the air even further and delivers it into the storage tank.
 
Oiled or Oil Free
If you can't remember the last time you checked the oil in your car, you should stick to an oil-free compressor. They have permanently lubricated bearings and don't require oil changes but are usually noisier, direct drive, and designed for home and not commercial use. Oil lubricated compressors have automotive pistons and rings with dippers on the bottom of the connecting rod which splash oil around to lubricate the bearings and cylinder walls. Just like any engine, keeping the oil at its proper level is required to ensure a long lifespan. Oil and filters should be changed every 500 hours of use and the compressors should be used on level surfaces to guarantee the motor stays lubricated.
 
Direct drive versus Belt drive
Direct drive compressors are connected directly to the motor shaft and turn at the same speed as the motor. Some have been designed to rotate up to twice the speed of the motor though they usually are louder. Belt drive compressors are quieter and better for continuous or high use. They last about 3-4 times longer than direct drive compressors but the belts need adjustments and may need to be replaced.

 

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Comments
Fuergrissa
Fuergrissalink
Thursday, February 10, 2011 10:44 PM
great article sarah, just a few things I've experienced that might be pertinent to other readers.

1. with electric compressors beware of misleading HP claims. Some compressors advertise both running HP and peak HP, some just running, and some try to pass off rediculous peak HP claims without specifying that it is peak hp. If comparing based on HP make sure your looking at the running HP rating, or better yet just go by the CFM rating, thats how air tools are rated so it's far more important.

2. buy the biggest compressor you can afford. when it comes to working on car's it's the most valuable power tool I own. many typical garage chores can be done on a typical 110v 3hp home use compressor. tools that are used in short bursts like impact wrenches, air ratchets, air hammers, and the like really don't care, but continuous use tools like HVLP paint guns, sandblasters, grinding and cutting tools all hog down a lot of air. since it's not always convenient to stop working while your compressor catches up (like when painting a car) that higher CFM rating is critical when you need it.

3. If you want a large compressor but only have 110v at your garage, compressors with gasoline engines are typically more powerful than even many 220v compressors.

4. If your really on a budget you can usually get great deals on partial or damaged compressors and refurbish them. electric compressor's are pretty easy to find with blown motors for dirt cheap. with a little time and effort it's not hard to attach a gasoline motor from a snowblower or lawnmower (as long as it has a horizontal shaft orientation), or even another electric motor that you can find on craigslist also. If the pump needs work search the model number and you can get rebuild kits with rings and seals etc.

5. And finally dont bottle neck your large compressor with small lines and fittings! My compressor is already under powered for sandblasting at 6.5hp it can only keep up with continuous use at about 70-75psi where it should be 90+. But when I was using 50ft of 3/8in line with 1/4 in fittings I had a 20ish psi preassure drop leaving me with only 50-55psi at the blaster!. Moving up to 1/2in line with 3/8 quick connects would mean loosing less than 5psi on a 50ft run of hose.

sorry for such a long comment >.<;
Peter Medina
Peter Medinalink
Friday, February 11, 2011 5:15 PM
Sarah, you're going to hate me a little. But there are roots blower and centrifugal blower compressors out there.

At Synapse, we use a Palatek 15 HP unit with a 120 gallon tank rated for 100% duty and 55 CFM @ 125 psi. One of the biggest considerations for us was the noise. The smaller blue unit is actually louder than the big green one. We have the big green one for high demand, although it is expensive to run. At 5 days continuous 15% duty, was about $200 in electricity wired for 220V, since we don't have 430V to the building.

The big green one has an aftercooler to cool the charge and separate the oil. You CANNOT breathe the compressed air from this unit. It has a formal oil filter, air intake and microprocessor controller. The little blue one is a medical unit with clean dry air and a dessicant filter for research use. We can actually breathe the air from the little blue one if we have to put a mask on, or wear a fully sealed suit.

Palatek Compressor

Here's an IR centrifugal

http://www.ingersollrandproducts.com/IS/Category.aspx-am_en-12995
tyndago
tyndagolink
Saturday, February 12, 2011 8:11 AM
If you can afford it, and are going to work near it, get a screw type. The IR screw type are quiet enough to talk next to. The old piston compressors are loud enough to wake the dead, and draw noise complaints.

http://www.ingersollrandproducts.com/IS/Product.aspx-am_en-35559

Peter Medina
Peter Medinalink
Saturday, February 12, 2011 2:57 PM
Kaeser always has that display at SEMA with a unit that runs the entire show, you can't even tell it is on. Pretty awesome. $10k awesome . . . ehh, not for most.
Cody
Codylink
Sunday, February 13, 2011 4:47 AM
My housemate picked up an air compressor last summer. He'd been talking about getting one for probably a year prior, but I'm a cheap ass and kept persuading him to just man up and do some hand work.

However, we wound up spending a lot of time in one of those rent-a-bay garages doing work on his Mazdaspeed3, and (obviously) had a lot of time saved thanks to their compressor. Meanwhile, I was wrenching on my WRX in our garage with hand tools. The difference became apparent very quickly.

Basically, thanks for the info. I'm going to be getting a place of my own in a few months, and I'm sure before long I'll be looking to buy one of these.
M-P
M-Plink
Sunday, February 13, 2011 5:05 AM
Sean, I just looked up those IR screwtype compressors and damn are they expensive. The 5hp, 150psig model is $4200.

Peter Medina
Peter Medinalink
Sunday, February 13, 2011 6:21 AM
I bought one of those $50 portables from Craftsmen for doing demos and I really don't know how you can get anything done with one of those units.

Keep an eye on Craigslist, reciprocating, industrial looking, American made, compressors with random names are what to look for.
OMG Its Weasel
OMG Its Weasellink
Sunday, February 13, 2011 1:39 PM
heh, nice to see that porter/cable mini compressor getting some love.
when i lived in a cramped apartment with a bunch of non-car people, its little size was a godsend, especially since i lived downstairs below the level my car was parked.
just used it the other day to put baseboards in with a nail gun, fucking righteous.
great topic, hardly ever talked about enough.
Rockwood
Rockwoodlink
Sunday, February 13, 2011 6:27 PM
RE: generators, you can run a 110v model easily on a 3000w+ generator (almost 30a @ 110v). We run my pancake compressor on a 4500w Onan in our toyhauler with ease. I've run one on a Honda eu2000i as well, but had to turn off eco mode (or whatever the variable idle thing is) to keep it from stalling.

My dad has an older Crafstman (1980s) with belt drive. That thing is the quietest home-use compressor I've seen, and still has pretty good numbers (can run a sandblaster continuously).
bigdave
bigdavelink
Sunday, February 13, 2011 7:27 PM
Hey Sara, could you do something on welders like you've done with this article? Im interested in your critique of harbor freight welders.
Sarah Forst
Sarah Forstlink
Tuesday, February 15, 2011 4:50 PM
Great comments everyone- thanks!

Peter, I hate you ;). J/K, I found some turbocharged compressors, but not really practical for using at a house. This is the next tool I'd love to have: http://www.sears.com/shc/s/p_10153_12605_SPM2350966801P?sid=IDx20101019x00001a&ci_src=14110944&ci_sku=SPM2350966801
64hp welder/generator/air compressor. Just under $30k on sale. Seems like a steal right?

@ bigdave, I'd love to get to welders. We'll see what I can find in the project garage budget this year. Stay tuned.
André Vicente
André Vicentelink
Wednesday, August 03, 2011 10:46 AM
hey. first up great tips, loved the post.
i'm new to the forum and i realy dont now how it works but i thought it would be apropriate to ask here, so heres the thing i have this realy old air compressor, runs with oil a belt and i think 2 cilinders, but it has been sitting in the portch for over 8 years, it doesnt have deep rusting problems, at least on the outside but im still afraid to plug it in. anyone know how i should proceed? should i replace all gauges, i know i sould replace oil but any tips would be mutch apreciated. sory if i caused any inconvinience.
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