Roughly what reading on an inches-of-mercury vacuum gauge corresponds to 25 mm Hg absolute?
Recovery requirements · EPA 608 Type III. The correct answer, and the reasoning behind it.
Evacuation levels for low-pressure appliances, and major versus non-major repairs.
The question
Roughly what reading on an inches-of-mercury vacuum gauge corresponds to 25 mm Hg absolute?
- About 25 inches of Hg vacuum
- About 15 inches of Hg vacuum
- About 29 inches of Hg vacuumCorrect answer
- About 10 inches of Hg vacuum
Why “About 29 inches of Hg vacuum” is correct
25 mm Hg is just under 1 inch of mercury measured from a perfect vacuum. Standard atmosphere is 29.9 inches of mercury, so a gauge that reads vacuum below atmosphere would show roughly 29 inches of Hg vacuum at 25 mm Hg absolute.
Source: 40 CFR 82.156(a), Table 1; EPA: Test Topics
Why the other answers are wrong
- About 25 inches of Hg vacuum — This mixes up millimetres with inches; 25 mm Hg is only about 1 inch of mercury absolute.
- About 15 inches of Hg vacuum — 15 inches of Hg vacuum leaves about 15 inches of mercury absolute, far above 25 mm Hg.
- About 10 inches of Hg vacuum — 10 inches of Hg vacuum is a shallow vacuum used for some higher-pressure appliances.
Practice more of this
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Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.