The Wrencher

With the gap between professional and personal thinning each passing day thanks to makeshift home workshops where weekend warriors cater to their DIY urges, there has been an increased demand for tools like air compressors which are used to power most of the air tools like air impact wrenches, air drills or air hammers.

Today, it is not uncommon to find these tools at home and being put to good use at that. Woodworking, automobile restoration and repairs, spray painting or just refilling a cylinder and an air compressor is at the heart of any such tool.

And if you believe that we are talking about the tank-sized monstrosities of yore, then you are clearly not aware of some of the compact versions of air compressors.

These pocket sized machines, well, not exactly pocket sized, but super compact machines are silent, efficient and can be lugged around for an emergency situation. 

The only caveat here is that these machines come in a plethora of shapes, sizes and configurations with a lot of technological gibberish thrown around for good measure. For a newbie, that’s as overwhelming as it can get.

Since we have been focusing a lot lately on best air impact wrenches so, we figured that this was just the perfect time to create a buying guide catering to air compressors that separates fact from fiction and gives you a clear picture of what to look for and what factors to overlook while buying one.

Grab a bucket of popcorn, sit back and enjoy the read.

How to select an air compressor

The first and most important aspect of your air compressor purchase is to be aware of the requirements from the compressor. It goes without saying that you’d be aware of how a compressor works. But just in case, someone has come here uninitiated, here’s some basic know how.

Air compressors are machines that utilize the pressure generated by compressed air to power pneumatic tools. That’s a simple way to put it.

So, the type of compressor you pick should be able to generate enough pressure to power the tool. Not all air compressors for example, can power a roller coaster or heavy duty machinery. We can categorize air compressors into three distinct types based on their applications.

1. Consumer air compressors: These are small sized devices, which may either be portable or stationary and are used for powering small to medium sized tools. Some of the typical tasks that can be accomplished with one of these are inflating tires, powering a stapling gun or caulk gun. Consumer air compressors may have a tank to store the compressed air (Piston-type) or may not have a tank, in which case, it will work continually for as long as you need compressed air.
2. Professional air compressors: These are more powerful machines that are designed for use in a commercial set up (think a job site). These are usually portable or can be hooked on to a vehicle for easily transporting from one job site to the other. Professional air compressors can be used for powering repair tools like nail guns.
3. Industrial air compressors: These are the most advanced category of air compressors that can work incessantly to power multiple air tools at the same time. Industrial grade air compressors are usually found in auto service centers, oil rigs and other industries that demand superior technology and performance. These are stationary units.

The Power Source

The power source of an air compressor is an excellent way to determine if it can match the power requirements of your tools. Gas powered air compressors are more powerful and are usually used in an industrial set up. The tradeoff for the extra power is that they can emit fumes, which is pretty obvious given that they are powered by gas. You either need an excellent ventilation system or you need to use these outdoors.

Compressors powered by electricity on the other hand are more suited for home as well as small-scale professional use. Standard sized portable units can be run on household voltage which is 110-120V in the United States. If you are using a bigger sized unit, then the power requirements may differ. Experts recommend that you do not power an air compressor using a generator because there is a risk of it damaging the motor.

CFM

Now we get into the trickier part and I will try to keep it as simple as I can. CFM stands for Cubic Feet per Minute and it determines the volume of air that the compressor generates for sending into the power tool. This is hands down, the most important number that you’d want to be aware of. If the CFM is not sufficient, you’ll have downtime where the machine tries to catch up with the demand of the tool thereby interrupting your workflow. What makes this tricky is that the CFM number will vary depending on the PSI of the compressor. So, if you are using two different tools, you cannot add their CFM ratings together to get a maximum number unless their PSI numbers are the same.

A rule of thumb that is generally followed by professionals is to use the Standard CFM rating of the tools at the same PSI to determine the maximum CFM that you need. For example, if you are powering a spray gun which runs at 8.0 CFM @ 30 PSI and a nail gun that runs at 10 CRM @ 30 PSI, you can add these together to come to 18 CFM @ 30 PSI as your max.

I know that sounds confusing. But that’s the best explanation that can be put forth.

Typical CFM Requirement For Various Tools:

Tool Type	Req. CFM's	Tool Type	Req. CFM's	Tool Type	Req. CFM's
Angle Disc Grinder	6 CFM	Dual Action Sander	6 CFM	Ratchet 1/4"	3 CFM
Air Drill 1/2	4 CFM	Grease/caulking Gun	4 CFM	Ratchet 3/8"	4 CFM
Air Drill 3/8	4 CFM	High Speed Grinder 5"	4 CFM	Sand Blaster	4 CFM
Butterfly Impact	3 CFM	Impact Wrench 1/2"	5 CFM	Spray Gun	6-18 CFM
Air Hammer	4 CFM	Impact Wrench 3/4"	7 CFM	Straight Line Sander	7 CFM
Cut Off Tool	4 CFM	Nailer	1 CFM
Die Grinder	8 CFM	Orbital Jitterbug Sander	6 CFM

HP (Horse Power)

Manufacturers often throw around the Red Line HP which is also known as the exploding HP in the advertisements for consumer grade compressors. But that’s a very misleading number because it indicates the HP at which the tank would explode. A true HP rating, which was used in the earlier days, would indicate the actual CFM that the compressor can produce. For example, 1 HP roughly equates to 4 CFM. So, a 6 HP compressor should approximately be able to produce 20-24 CFM. Try to correlate these numbers to see if the HP rating is inflated on your compressor.

PSI (Pounds per Square Inch)

Usually, the PSI is not a very important number because even the smallest portable compressor can be put to use provided you know what CFM number you need. However, there is an advantage of a high max PSI if you are looking to buy an air compressor with a tank. The higher the max PSI, the more air the compressor can hold irrespective of the tank size. For example, a compressor with a 2 gallon tank that has a max PSI rating of 150 will equal a 3 gallon tank at 100 PSI in its air capacity. So, you can use a smaller unit instead of opting for a bigger one.

Tank size

The Tank size is not really relevant as long as you pick a compressor based on the CFM. The only situation in which a tank size matters is if you continually need air to power your tools. In such a scenario, the larger the tanks size, the better it is because your compressor will have access to more air before it stalls due to drop in pressure. This will prevent downtime if you are running against a deadline or working according to the clock. Portable air compressors for indoor use usually have tanks with a capacity of 2-6 gallons while industrial grade units have 60-80 gallon tanks. The larger the tank size, the more space you will need to store the compressor.

For operating air impact wrenches a 2-6 gallon tank size would be more than enough.

The Pump

There are different aspects of an air compressor pump that you’d want to know.

1. Single Stage Compressor: A single stage compressor, which can also be known as a Piston compressor is a unit in which the air is compressed a single time by a piston generating a maximum pressure of approximately 120 PSI before being stored into a storage tank. It can have one or two storage cylinders of the same size. Single stage air compressors are ideal for personal use or for a craftsman who uses it for DIY tasks at home or a small workshop.
2. Dual Stage Compressor: In a dual stage compressor, air is pressurized twice. In the second time, it maxes out at approximately 175 PSI and is cooled before being transferred to the storage tank. Dual stage air compressors are powerful tools and also pricier. For this reason, they are mostly preferred by factories and auto shops.

Oil vs. Oil Free

The very working of a compressor makes it necessary for the internal components and parts to be lubricated to ensure optimum performance. However, there are both oil lubricated as well as oil-free compressors each having their own share of pros and cons.

Oiled Compressors: Oil lubricated compressors are more efficient, durable and quieter as compared to oil-free models. However, due to the maintenance that is required and the weight, these machines are usually preferred for commercial or industrial use. There are two main types of lubrication systems in oiled compressors.

• Splash systems: Splash lubricated compressors have a small dipper positioned near the bottom of the rod that connects the piston. When the compressor gets activated, this piston is submerged into a tiny oil reservoir and splashes the oil over the crank case. This is a very effective way to lubricate the machine but often, the oil cannot penetrate into the deeper parts of the pump. 
• Pressure lubrication: Pressure lubricated models on the other hand have an oil pump that is driven by the crankshaft. Perfectly positioned passages inside the crankshaft direct the oil to the many parts of the pump.

Oil Free Compressors: Oil free compressors are lighter in weight and are perfect for in-house use since there is no residue of oil in the air that the machine produces. These can be operated even on bumpy surfaces, start like a charm even in winter and have an in-built Teflon coating that prevents the need for lubrication. Another advantage is that these are low on maintenance barring the air filter which will need periodic servicing and the storage tank which needs to be drained.

Storage and Portability

You always thought that you’d only need the compressor to inflate tires in your garage until one fine day, you realized that it would be great if you could get it to the roof to power a nail gun to fix those shingles. Unfortunately, you’d need to be a heavy weightlifter to pick that thing off the ground. Portability is usually a tradeoff for more power. But for home use, it is always better to have a portable air compressor. Most portable units have caster wheels or a handle which allows you to lift it off the ground. Also, portability is not just about the weight. The dimensions of the unit matter too. Slimmer models are easier to carry or transport from one location to the other. The same stands true for storage.

Noise

The noise that an air compressor generates is the most underrated aspect of the purchase. What most people are unaware of is that an increase in mere 5-10 decibels can almost double the sound that a machine generates. So, if you have a compressor that generates 60 decibels of sound, it will be twice as loud as one that generates 50 decibels of sound. Think of something that generates 80 decibels now. If the intended use of the generator is indoors and if you hate noise as much as I do, you’d keep an eye on that number while deciding on what unit to buy.

Other features

Last but not the least; here are a few other desirable features which can improve the lifespan of the compressor and ensure that you are picking a durable one.

• ASME Certified: While this is not mandatory, a certification from the American Society of Mechanical Engineers (ASME) can be used as a benchmark to gauge the quality and the durability of the machine.
• Auto power shut off: An automatic shut off feature in case of the compressor overheating can prevent it from getting damaged and also improve the lifespan. This is also called a thermal overload switch.
• Roll Cage: One of the advantages of a portable compressor is that you can lug it around from one place to the other. But apart from the tank, most of the other parts including gauges will be prone to damage. A roll cage or a shroud prevents the parts from getting damaged.
• Ball Valve Drain: Most compressors will have to be drained periodically to prevent rusting. The easiest way to do this is with a ball valve drain that’s like a simple faucet.