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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

A mechanic is inspecting a hydraulic system and observes small, fine air bubbles consistently present in the hydraulic oil visible in the reservoir. The pump sounds abnormally noisy, but there's no major loss of power. What is the most probable cause of this issue?

Fine air bubbles in the reservoir and pump noise without significant power loss are classic symptoms of air ingress (aeration) into the hydraulic system. This o

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Question: A mechanic is inspecting a hydraulic system and observes small, fine air bubbles consistently present in the hydraulic oil visible in the reservoir. The pump sounds abnormally noisy, but there's no major loss of power. What is the most probable cause of this issue?

Answer options:

  • The system relief valve is set too low
  • The hydraulic oil is overheating ✅ Ingress of air, likely from a loose suction line connection or faulty shaft seal
  • The hydraulic oil is severely contaminated with water

Correct answer: Ingress of air, likely from a loose suction line connection or faulty shaft seal

Explanation: Fine air bubbles in the reservoir and pump noise without significant power loss are classic symptoms of air ingress (aeration) into the hydraulic system. This often occurs due to loose suction lines, damaged O-rings, or a worn pump shaft seal, allowing air to be drawn into the system.

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