What does a vacuum decay test assess in a tank system?

• A. The rate at which a vacuum level decays inside the tank or interstitial space, indicating leaks
• B. The visual appearance of seals under vacuum
• C. The electrical conductivity of the tank material
• D. The color change of the liquid stored

Answer: (A)

Vacuum decay testing checks how well a tank system maintains a vacuum. The key idea is to evacuate the tank or its interstitial space and then monitor how quickly the vacuum level drops. If there’s a leak, air leaks in and the pressure rises—the faster the decay, the larger the leak. If the system stays tight, the vacuum decays very little over the test period. So this method directly uses the rate of vacuum loss to indicate leaks.

Visual checks, electrical properties, or liquid color don’t measure leak tightness in this way, so they aren’t relevant to assessing vacuum integrity.