An air compressor is a workshop machine that takes in air, squeezes it to a higher pressure, and stores it in a tank for later use. Compressed air can power tools, inflate tires, blow dust from parts, and spray paint. It matters because it converts electrical energy into a portable source of mechanical energy.
Understanding its parts helps students use it safely and choose the right compressor for a job.
A portable compressor usually uses an electric motor to drive a pump that forces air into a steel tank. As more air enters the fixed tank volume, pressure rises until a pressure switch stops the motor at the cut-out pressure. A regulator lowers the tank pressure to a safe working pressure for the hose and tool.
Gauges, relief valves, drain valves, and airflow fittings help control pressure, remove moisture, and prevent dangerous overpressure.
Key Facts
- Pressure is force per area: P = F/A.
- Common workshop pressure units include psi, kPa, and bar, with 1 bar about 14.5 psi.
- The ideal gas relationship is PV = nRT, so adding more air molecules to a fixed tank raises pressure if temperature is steady.
- Gauge pressure reads pressure above atmospheric pressure: Pabsolute = Pgauge + Patmospheric.
- Airflow capacity is often rated in CFM, meaning cubic feet per minute delivered to a tool.
- A pressure switch usually turns the compressor on at cut-in pressure and off at cut-out pressure.
Vocabulary
- Air compressor
- A machine that compresses air and stores it under pressure so it can do work through hoses and tools.
- Tank
- A strong pressure vessel that stores compressed air and smooths out the pulsing flow from the pump.
- Regulator
- An adjustable valve that reduces tank pressure to the working pressure needed by a tool.
- Pressure gauge
- An instrument that shows the air pressure in the tank or at the regulated outlet.
- Safety relief valve
- A spring-loaded valve that opens automatically if pressure becomes too high.
Common Mistakes to Avoid
- Using tank pressure as tool pressure, which is wrong because the regulator may lower the pressure before air reaches the hose.
- Ignoring CFM requirements, which is wrong because a tool can lose power even when the pressure setting looks correct.
- Leaving water in the tank, which is wrong because compressed air produces condensation that can cause rust and reduce tank safety.
- Blocking or disabling the safety valve, which is wrong because the valve protects the tank from dangerous overpressure.
Practice Questions
- 1 A compressor tank has a gauge pressure of 120 psi. If atmospheric pressure is 14.7 psi, what is the absolute pressure in psi?
- 2 A nailer uses 2.0 CFM and a sprayer uses 4.5 CFM. If both run at the same time, what minimum compressor airflow rating is needed before adding a safety margin?
- 3 Explain why a compressor can have a high tank pressure but still fail to run a high-demand air tool continuously.