Vacuum Acceptance | Pump-Down, Leak, Pressure Rise and Gas Load

Evidence

Engineering assessmentVacuum measurementFAT recordProject-specific checks

Volume

Pumping

Conductance

Gas load

Pressure record

Check	Calculation / record	Acceptance question
Pump-down	P(t), V, pump configuration, valve state	Does the curve match the declared pumping system?
Pressure rise	Q = V·dP/dt	Is pressure rise compatible with leak/outgassing criteria?
Effective pumping	S_eff^-1 = S_pump^-1 + C^-1	Is speed at chamber sufficient, not only nominal pump speed?
Process gas	P ≈ Q_gas/S_eff	Can the system hold target pressure during gas flow?
Leak test	helium leak detector report	Are all ports, feedthroughs and seals verified?
Documentation	raw logs, calibration data, FAT protocol	Can the acceptance result be repeated and audited?

Possible real leak, high outgassing, wrong gauge position, pump contamination or open gas path.

Possible conductance constraint, water load, large internal surface area, trapped volumes or insufficient roughing path.

Outgassing or virtual leak can dominate; a straight pressure-rise slope is not the only possible pattern.

Effective pumping speed for process gas is not sufficient at the chamber interface.

Record	Required content
Configuration	chamber volume, pump types, valve positions, gauges, gas lines, tested ports
Pump-down	pressure-time curve from atmosphere or defined start pressure
Ultimate pressure	gauge type, location, time at pressure, pump status
Pressure rise	isolated volume, start/end pressure, duration, calculated Q
Leak test	method, sensitivity, tested locations, acceptance criterion
Gas-flow test	gas type, flow rate, pressure, pumping mode, stability

Observed value	Possible physical source	Record needed	Weak conclusion to avoid
Slow pump-down	Conductance criterion, outgassing, contaminated surfaces, pump constraint.	Pump-down curve, chamber state, pump configuration.	Assuming a leak without isolation data.
Fast pressure rise	Real leak, virtual leak, outgassing or trapped volume.	Q = V · dP/dt, helium test, vent/bake history.	Using base pressure alone as acceptance.
High pressure under gas flow	Insufficient S_eff, conductance loss, local gas injection or gauge position.	Gas-flow calibration, pressure under flow, pumping path.	Empty-chamber vacuum means process readiness.

Record: Pump-down curve, pressure-rise test, helium leak test, gas-flow data and raw FAT logs.
Interpretation: Ultimate pressure is separated from leak, virtual leak, outgassing and operating pressure under gas load.
Project use: Acceptance must be tied to chamber volume, process gas load, effective pumping and contract criteria.