Air Compressors

Piston or screw compressors, oiled or oil-free:

the split comes down to how long the machine has to run without a rest. A piston compressor fills its tank, stops and cools off, so it suits work that comes in bursts: inflating tyres, nailing, blowing out a radiator. Small oil-free ones are light and need no oil, but they are loud and wear out sooner. An oil-lubricated cast-iron pump driven by a belt turns slower, runs cooler and outlasts several of them, which is why workshops buy those. A two-stage pump is the step up for a shop that runs air tools all day. A rotary screw compressor, from makers such as Atlas Copco, Kaeser or Ingersoll Rand, is built to run continuously, suits a factory or a packing plant, and mostly needs three-phase power.

Air delivery, voltage and tank size on a compressor:

read the delivery in CFM at 90 PSI and compare it with what your tools draw, leaving a margin. A spray gun drains a small compressor in minutes; a nailer barely registers. Horsepower on a cheap label is often a peak figure, and the tank only stores air. Check the voltage as well. Small units plug into an ordinary 120 V socket, while 60-gallon machines run on 240 V single-phase, which Costa Rican houses are supplied with, usually on its own circuit. Where there is no power at all, a gasoline compressor with a Honda engine does the job on a farm or a building site; if you plan to run an electric one off a planta eléctrica, size the generator for the motor’s starting surge, not its running load. For paint, clean dry air matters as much as volume, so budget for a water trap.

The pump head, the tank and the price of a workshop compressor:

a belt-driven 60-gallon compressor on 240 V is around ₡1 million new, and screw compressors start near ₡4 million and climb quickly with size. On a used piston machine the price comes down to two parts. The pump head can be rebuilt or replaced, and heads, pressure switches and filters are sold separately under industrial parts, so a tired pump is something to negotiate over. The tank cannot be repaired: once it has rusted, the machine is worth its motor and its pump and nothing more.

Tank rust, oil blow-by and the check valve on a used compressor:

start at the drain valve under the tank. Water condenses there with every run, and in air as damp as Costa Rica’s a tank that was never drained rusts from the inside, where you cannot see it. Open the valve: a little clear water is normal, a gush of brown sludge is not. Look for bubbled or weeping paint along the bottom seams, and walk away from any tank with a welded patch. Then time a fill from empty against a similar new machine; a slow fill points to worn rings or valves. Oil mist at the breather or oil in the air line means the rings are going, and milky oil means water has reached the crankcase. A short puff from the pressure switch at shut-off is normal; a hiss that keeps going means a failing check valve. On a screw compressor, ask for the hour meter and the record of oil and separator changes.

Selling a compressor that came out of a body shop or a tire shop:

buyers will assume a workshop compressor ran all day, so say how it was really used. Give the tank size, the delivery at 90 PSI from the label, the voltage and phase, and whether the pump is oiled or oil-free, and photograph the data plate, the drain valve and the underside of the tank. A short video of it filling from empty with the gauge in shot answers the first question everyone asks. Say whether it is bolted to the floor or wired into the panel: someone driving from Liberia to see a compressor in Cartago wants to know if it can leave with him that day, and a 60-gallon tank takes two people and a pickup.