How to Buy a Used Air Compressor for Drilling
A drilling compressor is sized by two numbers — how much air it delivers and at what pressure — and almost every buying mistake is a mismatch between those numbers and the hammer they have to feed. A compressor that is close but not quite enough does not drill slowly; it drills badly, and it destroys hammers.
Beyond sizing, the questions are the same as for any large diesel machine, with airend condition dominating.
Size it against the hammer, with margin
Down-the-hole hammers specify a required free air delivery and a working pressure. Get both from the hammer manufacturer for the bit sizes you run, then confirm the compressor meets them with margin rather than exactly.
Margin matters because delivery falls with altitude, ambient temperature and wear. A compressor that just meets the requirement when new and cool will not meet it on a hot day at altitude with a few thousand hours on it.
Remember the hole itself consumes air. Deeper holes, larger annulus and water inflow all increase what you need, and a compressor sized only for the hammer will disappoint on the deepest holes you drill.
Airend and drivetrain
The airend is the machine. Ask for its hours separately from the engine’s, because they are frequently different, and establish whether it has been overhauled or replaced.
Ask for oil analysis. On a rotary screw compressor, oil condition and any metal in it is the clearest signal about the airend you will get short of stripping it.
Listen to it running under load, and check discharge temperature. A compressor running hot is either short of cooling or working harder than it should to make the same air.
Cooling, filtration and air quality
Check the aftercooler and the radiator for damage and blockage. These machines live in dust, and cooling capacity lost to a blocked matrix shows up as high discharge temperatures and shortened airend life.
Inspect the intake filtration and ask how often elements are changed. Dust ingestion is the main killer of airends in drilling service.
If the work needs dry air, establish what treatment is fitted and its condition.
Where it can work
Engine emissions tier decides where the machine can be used and, in some jurisdictions, registered. Confirm the tier and check it against every market you operate in.
Establish how it is mounted — skid, trailer or truck — and confirm that suits how you move plant and how you get onto the sites you work.
Inspection checklist
- Required free air delivery and pressure obtained from the hammer manufacturer
- Compressor rated with margin, not exactly to the requirement
- Altitude and ambient temperature at your sites accounted for
- Airend hours established separately from engine hours
- Airend overhaul or replacement history established
- Oil analysis reviewed, or a sample taken before purchase
- Machine run under load with discharge temperature watched
- Aftercooler and radiator inspected for damage and blockage
- Intake filtration inspected and change interval established
- Engine emissions tier checked against your markets
- Mounting arrangement suitable for how you move and site plant
Frequently asked questions
How much air do I actually need?
Take the required free air delivery and working pressure from the hammer manufacturer for the bit sizes you run, then add margin. Delivery falls with altitude, ambient temperature and wear, and deeper holes with a larger annulus consume more, so a compressor sized exactly to the hammer will underperform on your hardest holes.
Do engine hours tell me about the airend?
Not reliably — they are frequently different machines by history, since airends get overhauled or replaced. Ask for airend hours separately, and for oil analysis, which is the clearest signal available short of stripping it.
What kills drilling compressors?
Dust and heat. Ingested dust destroys airends, and lost cooling capacity from a blocked aftercooler or radiator shortens their life. Inspect the filtration and the coolers, and ask how often elements were changed.
Browse air compressors on Piling Broker or read the other buyer’s guides.