I am well and truly blown. Or at least blowable. 36 gallons worth give or take and that’s a might big blow job. Way more than quarts.
Big, I tell you.
Almost 40 years ago I built a pretty useful compressor for ordinary tasks. I got a really good deal on a twin cylinder compressor head that someone had returned to Sears. Graingers gave me the industrial price for a 2 HP, 220 volt, motor that ended up as an “extra” on a business project. I welded up some steel plate and angle iron for a mounting base.
The only shortfall of this project was the storage tank.
It took a while to get the plumbing right since the compressor owners manual had no installation instructions, the controller I found had no labeling, and there was no Internet.
Air compressors are pretty simple: motor, pump, accumulator tank, pressure regulator, relief valve, and some plumbing connect the pump to the tank and the tank to your air tools. The compressor pump works like the engine in your car. A motor turns a crankshaft to push a piston up and down in a cylinder. As the crank pulls the piston down, the vacuum it creates draws air into the cylinder through an intake valve. As the crankshaft continues to rotate, it pushes the piston back to the top of the cylinder, compressing the air in the cylinder. Near the top of the stroke, the compressed air gets pushed out through the exhaust valve. You could simply connect an air tool or tire chuck to the pump but that means the motor has to run constantly. That wastes electricity and a lot of compressed air so an air tank holds the excess air until we need it.
I hate waste.
The bigger the tank, the more efficient a compressed air system is in a garage or production shop because, just like your household water well, the motor needs to run only to refill the tank.
The size of an air compressor is measured by its output, not by the motor. We need to know the volume, measured in cubic feet per minute (cfm), and the pressure, measured in pounds per square inch (psi), to know if the system will do the job we need. When I built race cars and boats, we needed to run air tools that have specific demands. Most $100-200 “home-shop” air compressors can produce 3-5 cfm at 90 to 100 psi.
A compressor with lots of capacity and an upright tank is handy because it takes up the least amount of floor space in the shop and is usually on wheels so it can be rolled to the job. My neighbor has a nice $375 Dewalt 15-gallon, upright compressor on wheels that delivers 5.4 cfm at 90 psi and can run up to 150 psi. It will run my board sander that requires 3 cfm at 90 psi or my air grinder that needs a little more but not both. My new framing nailer can suck down the typical 1 HP, 6 gallon home-shop compressor.
And nothing I own can run a commercial sandblaster.
Before we started trying to tip this rary, I said that my storage tank was too short. The pump and motor combination I assembled yields 5.6 cfm at 150 psi or 6.7 cfm at 100. That’s plenty. Unfortunately, I have always used my little 5 gallon portable racing tank for storage, so the motor cycles more than it should.
As an aside, I like the little 5 gallon tank when all I need to do is pump up the soft tire on the lawn tractor, a chore it needs each time we use it. It takes less than a minute and only a ha’penny’s worth of electricity to do that instead of a couple-three-four minutes and a whole penny’s worth. I dislike waste.
I have always wanted to replace the tank with something bigger.
I found a couple of interesting air tanks on Craigslist last week. Each one was listed at $20. The first, a “former dental office” fixed tank with feet was reputed to be about 20 gallons and the second was a light-duty 11 gallon portable. I wanted the first but could make do with the second. After all that one alone would triple my storage capacity.
We definitely drove over the river and through the woods to get to the first tank; it was halfway down the state on Mallard Road. The “turn onto dirt” should have clued me it would be an adventure. Down and up and down and up a looooooooooong dirt road and the only thing I could think of was, I wonder who has to plow this? I’ve been in Vermont too long. The owner had built a wonderful, cement floored barn and wood shop on top of a hill with great views. He built his house there, too. And, yes, he does have a plow truck as well as a chain-shod square-bodied woods truck.
He was consolidating tools so he also had for sale a lovely cast iron table Craftsman 10″ table saw with base and extension. I would have liked it if I didn’t already have a saw. The Air Techniques medical/dental tank does measure out to be about 19 or 20 gallons in size, liquid measure, and has an apparently good Square D pressure switch and a labeled working pressure of 150 psi. Sold.
The other seller lives closer to North Puffin where he had a Formula V under a tarp on a trailer as well as a 60s VW and a 356 Porsche coupe in primer and bondo in his garage. He raced Porsche Speedsters in E Production class about the time I was racing Camaros so we know a lot of the same people. It’s not often I find another SCCA guy near North Puffin so that was a treat.
He sold me the $20 tank for $15 because I showed him the real $20 super tank in the back of the truck.
So now I have three tanks, two sets of controls, one compressor head, one motor, and a project. I saved two tanks from the recycler by reusing them for a cost of $35 and 135 miles on the truck. My next trick is to manifold it all up to get them to work either into one little, one big, or even all three tanks at once.
Of course Craigslist also had another nice used horizontal tank with a two 15 hp 3-phase motors turning two different 4-piston/compound pumps for about $1000. I’m not sure how I would have moved it, much less where to put it but a boy can dream…