Ranked by decibels: noise first, airflow secondQuietest we list: CAT-1P1060S · 56 dB
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Parts of an air compressor (labeled diagram)

The main parts of an air compressor are the motor, the pump that compresses the air, the tank that stores it, and the controls and safety parts on the tank: check valve, pressure switch, safety relief valve, gauges, regulator, coupler and drain valve. The diagram below shows where each one sits.

Updated October 18, 2026By the Silent Air Compressor editors · How we pick

Labeled parts of an air compressorA motor drives a pump that draws air through an intake filter and pushes it through a discharge tube and check valve into the tank. A pressure switch, safety relief valve, gauges, regulator, coupler and drain valve are mounted on the tank.123456789101112
  1. Motor
  2. Pump (cylinder & piston)
  3. Intake filter
  4. Discharge tube
  5. Check valve
  6. Pressure switch
  7. Safety relief valve
  8. Tank pressure gauge
  9. Regulator & outlet gauge
  10. Quick coupler (outlet)
  11. Air tank
  12. Drain valve

What each part does

1. Motor

Turns the pump. Portable compressors use 120V motors; shop units often use 240V induction motors. Slow-turning motors are a big part of what makes quiet compressors quiet. More in air compressor motors.

2. Pump

The cylinder, piston and valves that compress air. Oil-free pumps need no oil; oil-lubricated pumps last longer under heavy use. See how the pump works.

3. Intake filter

Cleans the air entering the pump and often muffles intake noise. Check it monthly.

4. Discharge tube

Carries hot compressed air from the pump head to the tank. It gets very hot; don't touch it while running.

5. Check valve

A one-way valve where the discharge tube meets the tank. It lets air into the tank and stops it flowing back to the pump. Symptoms of a bad check valve.

6. Pressure switch

Starts the motor when tank pressure falls to the cut-in point and stops it at cut-out. Most include an unloader valve that vents the discharge line when the motor stops, making the familiar "pssst".

7. Safety relief valve

Opens automatically if pressure rises above a safe limit, for example if the pressure switch fails. Never plug, remove or adjust it. More on relief valves.

8. Tank pressure gauge

Shows how much air is stored in the tank.

9. Regulator and outlet gauge

Sets the pressure sent to your tool, which is always lower than tank pressure.

10. Quick coupler

Where the air hose connects. Coupler style (industrial/M, automotive/T, ARO) must match your plugs.

11. Air tank

Stores compressed air so tools can draw bursts without the pump running constantly. Steel tanks rust inside if not drained.

12. Drain valve

At the lowest point of the tank. Open it after each use to release condensed water. A corroded, leaking or dented tank should be retired by a professional, not repaired.

Shopping for a replacement? See our air compressor replacement parts guide.

Safety first: switch off and unplug the compressor, then drain the tank completely before loosening any fitting, valve or line. Compressed air stored in a tank can turn a fitting into a projectile. Wear eye protection. Leave tank damage and electrical work on motors to a qualified technician.

How the parts work together

  1. You switch the compressor on; the pressure switch closes because the tank is below cut-in pressure.
  2. The motor drives the pump, which draws air through the intake filter and compresses it.
  3. Hot compressed air travels down the discharge tube and through the check valve into the tank.
  4. At cut-out pressure the switch opens, the motor stops and the unloader vents the line behind the check valve.
  5. You set the regulator to the pressure your tool needs and connect it at the coupler.
  6. As you use air, tank pressure falls back to cut-in and the cycle repeats.

Parts that wear first

  • Intake filter: clogs with dust; cheap and easy to replace.
  • Check valve: sticks or leaks, causing hard restarts.
  • Pressure switch: contacts wear, causing no-start or no-stop faults.
  • Rings and reed valves: on oil-free pumps, slow tank filling is the usual sign.
  • Regulator and couplers: seals leak over time.

Matching a symptom to a part? Our replacement parts guide has a symptom table.

Frequently asked questions

What part turns an air compressor on and off?

The pressure switch. It starts the motor when tank pressure drops to the cut-in point and stops it at the cut-out pressure.

What is the little valve that hisses when my compressor stops?

That's the unloader valve, usually built into the pressure switch. It vents the line between the pump and the check valve so the motor can restart easily. A short hiss is normal; a continuous hiss usually means a leaking check valve.

What is the most important safety part on an air compressor?

The safety relief valve. It vents air if tank pressure rises too far, for example if the pressure switch fails. Never plug, remove or adjust it.

Why does my compressor tank have a drain valve?

Compressing air condenses water inside the tank. The drain valve lets you release that water so the tank doesn't rust from the inside.