🔍 Key Concepts

• Evaporator vacuum stability and what affects it • Differences between air leaks, steam quality issues, and heat-transfer surface conditions • How each choice would behave: constant effect vs. fluctuating/oscillating effect

💭 Think About

• Which option would introduce small amounts of non‑condensable gases or air intermittently into the system? • Which conditions tend to cause a steady loss of performance rather than a constantly changing vacuum? • For each choice, imagine whether the symptom would be: (1) steady low vacuum, (2) gradually worsening vacuum, or (3) fluctuating vacuum, and match that to the question.

✅ Before You Answer

• Identify which options relate to air ingress/non‑condensables vs. those related mainly to heat-transfer efficiency • Decide which problem is most likely to cause a variable or pulsating vacuum rather than a uniformly poor vacuum • Double‑check that you are matching the symptom "fluctuating and unsteady" (not just "low vacuum") to the most logical cause