Choosing a shop air compressor for your aircraft build

Posted by Bill Miksich on

Most new builders come to us with two questions:

Q1: Looking for tank size/PSI/CFM recommendations that will work well with the tools.

Q2:  There are just too many choices out there. I’ve read through the hundreds of opinions on the vansairforce site and everybody has one. I really just want somebody such as yourself to guide me, even if it as simple as the brand. I know I’m going to need to spend $600-$900 on one and I can easily get a 220V outlet in the house. I’m going to be building in the basement (a walkout) and will have the compressor in the next room (furnace room). That should at least help with the noise. I could even put the unit in the garage and run a line down to the basement, but I don’t want the neighbors bothered and am afraid they’ll hear it in the garage (I really have no idea how loud they actually are). Can you offer any suggestions on brand and even model?

Actual Statement from a Customer: 

"After all the talk about air compressors, I feel like there are three main categories... Junk, Well-marketed but semi-junky, Professional."

OUR ANSWER:

Okay, more questions... 

On Horsepower, the rated HP on a compressor is just a measure of how much energy is used (watts).  Cheap motors use WAY more energy to do the same work as good quality motors.  I would assume that the pump is the same.  So you could have a 10HP import that makes less air than a 5HP quality unit.  Therefore HP is meaningless, as is the high end PSI that they like to claim.

On PSI (pressure in pounds / square inch).  All air tools are designed to run on 90psi with the exception of paint guns that are generally far lower.  So look for the CFM (flow in cubic feet / minute) rating at 90psi.  While a rivet gun will use 3-4cfm and a drill will use 8-12cfm, they don't run all the time.  If you figure that you are pulling the trigger on the drill well less than half the time, you don't need to match the cfm on the compressor... because of the tank.  The tank is like a battery and the 'compressor' pump is like the charger.  The pump is what has the CFM/PSI rating (charger size) and the tank volume is like the capacity of the battery.  The larger the tank, the longer it runs to charge up.  You really only need a tank large enough to buffer the difference between the time you pull the tool trigger and the time the pump gets up to full capacity plus the length of time you run the tool in one burst.  I am not a fan of larger tanks (see below).  One can also add a tank only to the system if you feel you need more storage.  A simple tee fitting anywhere in the airline will do.  

On Painting, will you painting it yourself?  Painting takes a ton of air and you will end up with a huge compressor, priming is not a problem because you don't need to keep a wet edge.

I like the compressors that are portable because:
  • You can take them out of the garage/basement and out to the hangar for final assembly and such (since they are 110v and on wheels).  
  • They tend to isolate vibration from the floor making them a bit quieter than the bolt down monsters.  
  • They are fine to run all air tools and primer guns at a 50% duty cycle.
  • I like the smaller tank size because they turn on and are ready quick... then they run when the noisy tool is running... then they turn off quick.  I hate larger tanks that are running to charge up while the rest of the shop is quiet, then silent when the tool is running.
Here are my two favorites:

My Reasoning:  cast pump, top quality, appropriate size and CFM, runs on standard outlet, belt driven, solid thus quiet (75-80db), portable to take to hangar later, free shipping or locally available. 

Shhhh! We are working here
  • Do look for models that are quiet to start with (cast iron, not aluminum), and be prepared to do some custom work to really quiet them down as you will listen to the compressor a lot.  If you end up with a bigger compressor that puts out 11cfm or so, you can change the belt and pulley setup to slow it down so it runs much quieter (but for a longer time).  
  • Look and try and find rattle traps and take mountings apart and buffer them with rubber washers and such.  
  • Also spin off the intake filters and use threaded iron pipe to plumb the filters into a baffle box or outside the garage/house.  60% of the noise from a piston driven compressor comes from the air intake.  Don't go outside with it if you have neighbors that you are concerned about.  Then a big softly lined plywood box with a large indirect opening would work to dampen the sound.  My goal is to get them quiet enough that I can hear the mechanical parts moving not the air sucking from the intake.
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Mike 

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