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Question

Difficulty: MediumPneumatic Tools and Compressors

During shop operations, an electric air compressor builds pressure in the receiver tank but fails to turn off once the tank reaches its maximum rated shutoff threshold. Which component has most likely failed?

  1. A
    Safety relief valve
  2. Pressure switchAnswer
  3. C
    Pressure regulator
  4. D
    In-line lubricator

Answer

Pressure switch
The pressure switch is an electromechanical control device wired to the compressor motor. It constantly monitors tank pressure via an internal diaphragm or bellows. When tank pressure reaches the preset cut-out limit (typically 120 to 150 PSI depending on the model), the switch mechanically forces the electrical contacts open, interrupting current to the motor. If the switch fails to open, the motor will run continuously.

Step-by-Step Solution

1
Analyze the operational symptom described in the scenario
The compressor motor continues running continuously past its upper pressure limit rather than cycling off automatically.
Identifying whether the failure is electrical (power control) or pneumatic (air containment/delivery) narrows down the suspect component.
2
Evaluate the function of electrical control components on an air compressor
The pressure switch directly controls the electrical power supply to the motor by opening contacts at cut-out pressure and closing them at cut-in pressure.
A failure to disconnect electrical power at the upper threshold points directly to stuck or defective switch contacts in the pressure switch assembly.
3
Differentiate between the pressure switch, mechanical relief valve, regulator, and lubricator
The pressure switch is the primary operational control for motor shutoff, while the relief valve is a mechanical safety backup and the regulator governs downstream tool pressure.
Eliminating secondary pneumatic conditioning and safety devices confirms the primary control failure.

Key Concept

Air compressor electrical control and pressure switch operation
Estimated Time:1m 0s
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Topics

Pneumatic Tools and Compressors

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