An air compressor are a system made up of several moving parts, all of which must work together. It’s a big, loud, clunky piece of machinery, so they’re tempting on secondhand market. The problem is that they’re simple.
So they gets beat up behind the scenes long before the sign show up. A rusty tank may look okay from exterior. And just because the motor spin doesn’t mean it’ll kick out the juice to build pressure.
How do you know if you’re getting a good deal… Or getting a headache for weeks? Here is what to check on used compressor.
Essential Steps for Checking Used Air Compressors
Inspecting the Air Tank for Rust
It all starts with the tank. Air compressor tanks is the quiet assassin. Examine the exterior for surface rust (which is usualy cosmetic) and pay particular attention to seams along bottom and near drain valve.
Since rust can be hidden in the inside, look closely at exterior for any signs of trouble. If you see any sign of holes, thinning metal, or bulges, leave immediately. A tank with corrosion issue is like having a bomb in your house.
It doesn’t matter how sweet the motor is if the container that hold the pressure has been compromised. Safety trumps all when it come to this component. If you even slightly doubt integrity of the tank, the unit are junk.
Checking Motor Sound and Oil
Finally, listen to the motor at load. Have the seller plug it in and run it. You’re listening for a consistent hum with no clicking or grinding sound.
If it has an oil sight glass, watch it. It should be clear or a slight yellow color. Dark brown to black indicates that engine was run either dirty or hot for quite some time.
Evaluating Pressure Build-Up Time
Seized crankshafts is not cheap, but oil is. How fast does it builds? How long does it take to get up to cutout pressure from zero?
It shouldn’t of been too long. If it’s slow, then the cause is most likely either a leaking valve plate or worn piston ring. The thing folks mess up on is thinking that if it gets to pressure it’s good.
Not true. Because if it take a compressor 10 mins to fill up, it wear out quicker and overheats quicker. It also causes you to wait longer than before.
Examining Filters and Air Hoses
Check the air intake filter. Typicaly this is just a paper or foam element. A clogged filter reduce airflow, which makes motor run hotter and have to work harder.
Replace it when needed, and if it is missing, get one now. Is it soaked with oil? The engine are breathing its own exhaust.
This is not good for its lifespan. A clean filter are one small indication that the owner was concerned with maintenance. Examine the hose connection and the discharge port.
Air tools hate moisture. Are any of the fitting showing leaks? Is the pressure switch shutting down the motor at the rated PSI?
Testing Valves and Electrical Safety
The motor should stop when gauge reaches the limit. A broken pressure switch can be an easy fix, but that also tell you the seller may have neglected something else. Look at the gauge.
Is it steady? If it isn’t steady and your needle drop, that means there is a leak somewhere (usualy in the unloader valve or the head). That’s bad but fixable.
However, it also tells you there is some wear internally. Knowing where the wear are helps when buying one so you can negotiate price with the seller. Check the plug and power cord for any fraying.
Are there any crack? Make sure you are using a proper main cable rather than an extension cord setup. Don’t sacrifice safety to save money!
Make sure ground is in place. A loose electrical connection can be deadly. Did they ever drain it?
Verifying Drainage History and Model
Get a history of the tanks’ drainage. It is supposed to get drained on a regular basis but water sit in it. Did they do that?
Ask the seller. If not, assume no. Rust form internally when moisture gets into the tank and will destroy compressor from the inside out. What model is it?
Find it online. Some models, such as those made by Harbor Freight or Craftsman, has common issues, while others like DeWalt or Bostitch have better parts availability. Knowing the moddern model also allows you to plan for repairs.
Check the unloader valve. The unloader valve relieve pressure on the head when motor cuts out. A bad one can cause your motor not to start.
It’s another easy replacement part but it’s also a frequent fail point. And lastly…look at the bottom line. How many hours will it take to have it running?
Calculating Total Repair Costs
What’s the oil change fee? What about filter? Don’t be fooled.
That’s money too. Running true is the only way a used compressor are a bargain. If you get a funny feeling, walk away.
Take the inspection as truth.
