There’s always that voice in the back of your head saying: “Go on, it’ll be fine for just one more time!” The truth, however, is that taking good care of your tools will make them last years longer and prevent them from dying on you at the most inconvenient moment. With good air compressors costing $200 or more, a little attention on a daily, monthly or yearly basis will save you a very worthwhile sum of money. Unlike light bulbs which go “poof” without warning, the components of rapidly moving reciprocal or rotary machines wear out over time. Regular oil changes slows this process significantly, while also reducing the heat put out by the compressor, which can prevent other problems from turning up.
Your compressor should have come with a manual, but if you’re like me, that wonderful little booklet has already long ago eloped to Spain with my drill press documentation. Never fear, it is not difficult, doesn’t take long and (should) not be a messy job.
How Often to Do It?
Many compressor users don’t even bother to open the condensate drain valve when they’re done for the day. Lo and behold, within months their valves or the tank itself has rusted, and good luck getting a vendor to fulfill that warranty.
Used oil contains all kinds of gunk that doesn’t belong in your engine and can eventually cause it to seize up. The amount of time spent running, at what temperature the compressor was working, and even the time spent standing idle all seem to have an effect. Contrary to some opinions, you can’t tell the difference between used and fresh oil just by looking at it, unless the new lubricant is straight from the bottle.
If you use your compressor only occasionally, you’ll find it difficult to keep track of how much time it’s recently spent pumping air. In this case, it can be a good idea to set apart some kind of special date (New Year, your birthday, etc.) and perform the necessary maintenance on everything you own. This way, you don’t take the risk of skipping a year or two and blowing up the compressor.
If you’re a professional user, you can either have a logbook for each piece of equipment or estimate the average number of hours each is in use per week. You do need a written maintenance log. This is good for insurance purposes, but mainly it prevents you from forgetting the things you were sure you’d remember
Understanding Your Compressor
In all likelihood, your trusty compressor consists of a pressure tank, an air pump, and a motor to drive the pump. On almost all models, both the motor and compressor need oil to function. However, once you’ve diligently looked at the thing from every angle and still can’t find an oil sump, it might just be an oil free model. All the lubrication it will need was added when it was manufactured, so fret not. Many hobbyist models are of this type.
The first thing to do is to locate the oil sump, which should not be difficult. It will have a drain hole near the bottom and a fill hole near the top, each secured with a threaded plug you’ll need a wrench to open (gently!).
Make sure that the compressor is not leaning to one side but standing on something level. Run it for a few minutes to heat up the oil, which makes it flow more easily and allows you to get more of the old stuff out.
Get your waste oil container ready. A rectangular plastic bottle with one side cut out is perfect: once you’re done, it’s easy to twist the cap off and empty it without spilling. Position the container under the drain hole, twist out the plug (preferably without dropping it in the oil) and just wait.
On an environmental note, one gallon of used motor oil is capable of contaminating one million gallons of groundwater, so find a place that can recycle it for you.
Now, just close up the drain hole, open the fill hole, and pour your lovely new lubricant in. Pro tip: turn the container onto its side to prevent it from gulping.
Use the correct amount: too much oil is bad for your compressor and too little even worse, especially if it doesn’t have a dedicated oil pump but relies on some kind of rotating arm to splash oil onto the working parts.
The Right Kind of Oil
As you probably know, all lubricants are not the same. Depending on expected temperatures, use cycle and special additives, the kind of oil you would put into a Ferrari will not yield the best performance when you pour it into a Toyota, and vice versa.
If your compressor is still under warranty, it makes sense to use the manufacturer’s recommended brand, even if it is overpriced, just in case the machine goes to The Great Junkyard in the Sky on day number 364. Other than that, unless you’ve been specifically told to use one kind and only that kind of oil, as will probably be the case with large, stationary compressors, just make sure you pick up “compressor oil” and not some other kind of lubricant. The reason for this is that compressor oil contains additives to counteract corrosion caused by high-pressure air. Any good hardware store should have what you need or be able to order in a specialty lubricant if that’s what you need.
And that’s how simple it is.