Dan Kerr makes due with two air compressors: a sort of glove-box model that can travel in vehicles, and a sizeable compressor in his shop.
Probably the most frequently used equipment in my shop is the air compressor. I acquired mine from a car wash years ago as a discard unit; the pump had worn out and the entire unit was changed off, purchase price: $50.
One January night in a snowstorm while hauling my tent trailer home from Florida, I got caught with a flat tire in New York State on Hwy. I90, which was bad enough until I dug out the trailer spare and found it flat! For the first time I unpacked my emergency glove box size air compressor; it worked perfectly and I was on my way.
As a result one of my compressors includes a small hand-held oil- less glove box model that’s kept in the truck. The other is my 1 ½ horse power (HP) 240 volt unit that delivers 7 cubic feet/minute (CFM) at 120 pounds per square inch (PSI) and has an 80 gallon receiver (tank) in a vertical position.
Compressors are available in everything from the hand held 12 volt to hundreds of horse power diesel powered units. The trick when shopping for one is to try to figure out what you are going to use it for. I emphasize “try” because I keep coming up with new uses for mine. Generally, the larger the size of the tank, the less the unit will have to operate. That’s a good thing.
What will you be operating with your compressor? Checking the CFM and PSI of the tools you might use and then comparing them with the air compressor specs will supply the numbers to answer the question.
Take my compressor, at 7 CFM and 120 PSI delivery. It will easily operate a good size ½” impact gun which consumes 3 CFM @ 90 PSI. Theoretically, if I was to turn on my compressor empty and pull the trigger on the air gun the compressor would be supplying two times the tool’s air consumption which means the compressor will pass the demand and eventually shut off. This is not how a shop runs, the compressor is usually full of air at the start of a job, and the air gun doesn’t run constantly but rather intermittently so in this example I have air over kill for my shop.
Auto body professionals will tell you that the larger the tank the better as constant air pressure is optimum for spray painting. The pulsation of the pump can be passed onto the air delivery through the paint gun and causes inconsistent spray patterns, which is the last of my worries.
My prime concern is how many times the 1 ½ HP motor will be running. With the current cost of hydro, the less time it runs the cheaper it is to operate.
So then what are the choices? The glove box one is self-explanatory. Ask for one for your birthday or Christmas instead of another unwanted sweater. They can be used for the tire pump ups like bicycles, wheel barrows, cart tires or your ATV. It could be all you ever needed; it’s inexpensive and it’s mobile.
If you are off grid or want mobility on a grander scale, engine powered units or (donut) compressors often used by contractors may be a choice. They offer a decent PSI and CFM delivery good enough for small pneumatic tools such as nailers or impact drivers. The down side would be the maintenance of the engine. The pumps are usually oil-less (which limits their longevity) and a very small tank means they will continually run. These are also available in a household 120-volt motorized version.
Next up the ladder is the mobile shop version that offers increased PSI, CFM delivery and tank size while maintaining a level of mobility. These are set up with the pump and motor on the top of a tank, a handle on the side with wheels on the bottom and are household current rated. Some of these are also oil-less and the pump and motor are attached which means if it goes kaput you will be buying an entire new unit — it’s cheaper to purchase the entire unit rather than try to fix it. If this happens, keep the receiver (tank) it can be used as an air pig on wheels.
From here up you are choosing between stationary models in a horizontal or vertical plane, which are configured with a separate pump driven by belts and a 240-volt motor.
If the day comes that I have to replace my compressor I will be looking for a similar size to the one which has served me well over the years and with proper maintenance should continue to do so. As a rule of thumb it is better to go with a slightly larger unit than you need. This will reduce run time, wear and tear, maintenance and overall expense. And don’t forget; never turn down a deal just because it may be a little too big.
- Dan Kerr