Vacuum Decay (Blank-Off) Test
The evacuation standing-decay verdict: from the micron level at valve-off, the level after a timed hold.
Example
You enter
- Vacuum at valve-off (microns) 300
- Vacuum after hold (microns) 450
- Hold time (min) 15
- Pass ceiling (microns) 500
You get
- Total rise 150 microns
- Rise rate 10.0 microns/min
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeThe evacuation standing-decay verdict: from the micron level at valve-off, the level after a timed hold, and the hold time, the total rise and the rise rate, with a tight-and-dry / moisture / leak reading against an editable 500-micron pass ceiling (ANSI/ACCA 5 QI-2015 (evacuate and hold at or below 500 microns) / AHRI field practice).
Formula or tablerise_micron = end_micron - start_micron; rate_micron_per_min = rise / hold_min. Verdict: end at or below the pass ceiling (default 500 microns) is tight and dry; above it is residual moisture/outgassing if it plateaus or a leak if it climbs steadily.
Source and editionFirst-principles standing-decay (blank-off) arithmetic (public); the 500-micron evacuation target and valve-off decay test are the common HVAC field convention (ANSI/ACCA 5 QI-2015 (evacuate and hold at or below 500 microns) / AHRI / equipment manual, by name).
Free accessThe rise/time arithmetic is public; the 500-micron pass ceiling is an editable field convention.
What governsEstimate. AHJ and licensed professional govern.
API field namesstart_micron, end_micron, hold_min, pass_ceiling_micron, rise_micron, rate_micron_per_min
- Pass ceiling default 500 microns at valve-off (editable); some manufacturers call for a deeper holdANSI/ACCA 5 QI-2015 (evacuate and hold at or below 500 microns) / AHRI / equipment manual
- Moisture vs leak a rise that plateaus below ~1000-1500 microns is residual moisture/outgassing; a steady climb that does not plateau is a leakfield practice
- Instrument read with an electronic micron (vacuum) gauge isolated from the pump, not the manifold compound gaugefield practice