Compressors operate on the principle of drawing in air, reducing its volume, and thereby increasing its pressure. The most common types, piston (reciprocating) and screw compressors, achieve this compression through different mechanisms. Piston compressors compress air via the movement of a piston within a cylinder, while screw compressors use two rotating screw rotors to compress air. In a normal operating cycle, once a specific pressure level is reached, a pressure switch (pressure sensor) detects this and signals the motor to stop or enter idle mode. When the pressure drops, it reactivates. If the compressor runs continuously without pressure buildup, there is a fault in this cycle.

Let’s examine the primary causes and technical details of such a malfunction:

• Air Leaks: This is often the most common issue in the system. Compressed air can escape from various points, including pipe lines, connection points, hoses, regulators, valves, dryers, and tank connections. Even a small leak can lead to substantial energy loss over time and cause the compressor to run continuously. The leak rate is directly proportional to the system pressure and the size of the leak orifice. For instance, a 1 mm hole at 6 bar can result in a loss of approximately 7 m³ of air per hour, which is a significant load compared to the compressor’s nominal flow rate.
• Clogged Air Intake Filter: The compressor’s intake filter captures airborne particles, protecting the internal components. Excessive clogging restricts the amount of air the compressor can draw in, reducing compression efficiency and forcing the compressor to run longer to reach the target pressure. A clogged filter increases the vacuum pressure (vacuum pressure) on the intake side, straining the motor.
• Check Valve Failure: The check valve, typically located between the discharge line and the air tank, prevents compressed air from flowing back from the tank into the compressor. If this valve is faulty (stuck, leaking, or broken), air from the tank will leak back into the compressor when it stops or enters idle mode, causing system pressure to drop. The compressor then reactivates to compensate for this loss, leading to continuous operation.
• Internal Compressor Wear:
  • For Piston Compressors: Worn or broken piston rings (piston rings), scored cylinder walls (cylinder walls), or leaking/broken suction and discharge valves (suction and discharge valves) can cause air leaks and reduced compression efficiency. Compressed air leaks back within the cylinder or through the valves, preventing pressure buildup.
  • For Screw Compressors: Increased clearance between the screw rotors or worn rotor seals (rotor seals) can lead to internal leaks. This reduces the compression efficiency of the screw element and causes the compressor to run continuously.
• Pressure Sensor/Switch Malfunction: The pressure switch or sensor measures the system pressure and controls the compressor’s start/stop cycle. If this component is faulty (inaccurate readings, calibration errors, electrical issues), the compressor may not detect that the target pressure has been reached and will continue to run.
• Discharge Line Obstruction/Restriction: An obstruction or restriction in the discharge line, which carries compressed air to the system, prevents the free flow of air. This can cause the compressor to operate under high pressure, leading to strain, while preventing the system from reaching the desired pressure level.
• Motor Underpower or Loose Belt: In belt-driven compressors, a loose or worn belt can prevent the motor’s power from being fully transferred to the compressor element. If the motor itself is not producing sufficient torque (e.g., due to low voltage or phase issues), it can prevent the compressor from running at its nominal speed, reducing compression efficiency.