When you're working indoors, an ordinary compressor can be pretty loud and distracting. The only other option is to invest in a silent compressor which can, easily, cost 3-4 times as much. More than that, unless you're ready to spend an obscene amount, they are rarely able to put out the same psi as a standard compressor.
To the do-it-yourself type, this isn't a problem. Using a standard fridge/water cooler compressor, an old pancake air compressor, and a bit of soldering skill, you can build your own SUPER silent compressor that is barely audible when running, and is capable of putting out, up to 120 psi safely. It operates a bit more slowly than it's mechanical counterpart, but not by much. This model can pressure up in under 4 minutes.
This project should take you, no more, than an hour to build in it's simplest form, however there's plenty of room to improve the design. Simple upgrades such as a custom mount for the fridge comp, a wire box to clean up the harness, etc. will go a long way to making your build prettier, but aren't necessary to it's function. There is almost zero vibration and as much noise as your refrigerator has when it's running.
Step 1: Tools and Equipment
pancake compressor with separate pressure switch
fridge or water cooler compressor, (either will work fine. The one in this instructable is from a water cooler)
1/4" copper line
various wire connectors/marettes
Important note: When locating your fridge/cooler compressor, it's a good idea to have it drained by a professional. Simply cutting the tubes and letting the gasses out is just plain bad for the environment, and a hazard to you if inhaled directly. If having it drained isn't an option, locate a unit that has been sent for recycling. More often than not they end up there simply because they've leaked all of their coolant and no longer provide refridgeration, however the compressor itself should still be operational. Nevertheless, you should still take precautions, when cutting the lines, by using a ventilator.
Soldering torch w/ solder and flux paste
Step 2: Identifying the Tubes/electrical on the Fridge Compressor
On the side of the unit, you'll find the thermal overload/power connection. In the second picture you can see the connections. You should make note of how it's connected when you remove it from the fridge/cooler and wire using the same colors, with the ground wire connected to the body of the unit itself. There is a thermal overload built into every unit that protects it. One flaw with a fridge compressor is that if you shut it off, then turn it on right away, the thermal overload will kick in. Don't worry if this happens. Just wait a few seconds and try again. The thermal overload should reset itself. It'll also protect the unit from power spikes, in case you fudge the wiring like I did on the first unit I built.
Identifying The Tubes:
More often than not you'll find three 1/4" tubes exiting the unit with one by itself on one side and the other two side by side on the other. An easy way to figure out what is what is to connect the comp to power then feel the end of each line for suction or discharge. On 'most' models, the suction tube is the one that's by itself, and the discharge tube is the lower of the two on the opposite side. The third tube is unused. It's called the process tube, and is generally only used at the factory for testing. This tube should be crimped and/or soldered closed.
Step 3: Important Choices on What Type of Air Compressor to Canibalize
The choice of air compressor you plan to use for this project is extremely important. I've built a few of these, for other people, and have found that the pancake models with the separate pressure switch tend to work the best. The larger models that incorporate the pressure switch into the power have a unique issue. There is usually a bleed valve, incorporated into these, that release the pressure going from the compressor to the tank. Unfortunately, this switch needs a strong pulse of air to activate, that the fridge compressor just can't provide, so it will leak incessantly, causing your tank to fill more slowly. You can disable the switch, however it's part of the pressure regulator in the unit, so you will also be disabling your compressor's ability to shut off when it's full, making it unsafe, or in the very least, annoying since you'll end up having to keep a constant eye on it.
Suffice it to say, having an air compressor with a separate pressure switch will make the job a whole lot easier.
Step 4: Installing the Fridge/cooler Compressor
Attaching the Fridge Comp. to the Tank:
For the sake of cost and simplicity, I simply zip tied the unit onto the tank. There is virtually no vibration and no worry about it working itself loose over time. You can choose to create a mounting bracket, for cosmetic reasons, however, if you're like me, it doesn't have to be pretty. It just has to work.
Soldering and shaping the Line:
You may need to solder new line and add fittings to make your connection, however more often than not, you can just recycle what came with the air comp, and the fridge. The line you see in the pic was existing from the air comp and was 1/4" I.D. (internal diameter). The line exiting the comp was 1/4" O.D. (outer diameter, so it was simply a matter of a bit of sanding to make the connection. The rest is simply soldering pipe together much as you would if you were working with plumbing. Just lay some flux paste in the joint, apply heat from the torch then let the solder fill the gap, and presto...you have a connection. You may need to make some dramatic curves in your line in order to get it to line up with the intake on the tank. I like to keep a piece of flexi-shaft from an old weed trimmer on hand for just such issues. You can feed it through the pipe, bend to the desired shape and then draw it out again. It's a great way to prevent kinks in the line that could otherwise interrupt the air flow.
I can't express, enough, how important it is to make sure you don't have any leaks. This is where the teflon tape comes in. Fridge comps. don't put out a lot of volume, so any leak, no matter how small can seriously impede it's fill time. Simply put, check every connection, and tape everything.
Step 5: Wiring the Power and Pressure Switch
This is just a simple diagram I made up for a friend that wanted to build his own unit. Should make the set up easier.
Step 6: Finished
Hope you enjoyed the instructable.