A compressor takes ordinary air, squeezes it and stores the pressure so a hose can carry power to a tool. On a job site that means breakers, chipping hammers, rock drills, sandblasting and tyre work run without a generator or a cord. Rented units run from small electric boxes for indoor trades up to towable diesel machines, and the towable class starts near $150 a day.
Two numbers describe every one of them
Pressure, in psi, is how hard the air pushes and it is roughly the same across the fleet, near 100 psi. Volume, in cubic feet per minute, is how much of it there is, and that is what runs out. A tool list adds up in cfm, so add the tools you will run at once and hire above that total.
Rotary screw or reciprocating
Towable job site machines are rotary screw: they run continuously, hold pressure steadily and are happy driving two breakers all day. The small electric units on the tool counter are reciprocating piston machines with a tank, built to fill and rest. Asking a piston unit to feed a continuous tool is the most common bad hire in this class.
What a rental compressor costs
Small electric units sit near $40 to $80 a day. A towable 185 cfm diesel machine is commonly $150 to $250 a day and $450 to $700 a week, with fuel on top. Bigger towable machines climb steeply from there, and yards usually put a longer minimum hire on the large ones because they are trucked rather than towed.
The machine is only half of the hire
A compressor with no hose is a heavy noise. Air hose in the right diameter and length, couplers, a filter or lubricator, and the tool itself are separate lines on the quote. Long or narrow hose loses pressure over distance, so tell the yard how far the tool will be from the machine and let them size the run.
Questions people ask about what is a compressor
How do I know what size compressor I need?
Look up the air consumption of each tool in cubic feet per minute, add up the ones that will run at the same time, and hire the next machine up the ladder. Rounding down is why crews end up waiting for pressure between blows.
Can I run a compressor indoors?
A diesel machine, no. The exhaust has to go outside, and yards will not sanction a towable unit in an enclosed space. Indoor work means an electric unit or a diesel machine parked outside with a long hose run through a doorway.
Does the rental include fuel?
Almost never. Towable machines go out full and come back full, or the yard refills them and bills it at a rate higher than the pump. Fuel is usually the second largest line after the rate on a week of breaking.