TL;DR

  • Run +3–8 mbar overpressure for most positive-pressure glove boxes.
  • Set relief valve to crack at +10–15 mbar so operators can’t over-inflate the chamber.
  • Tune make-up gas flow and circulation so gloves don’t “breathe” when you move.
  • Equalize the antechamber before opening the inner door—no slamming the box with pressure swings.

Why stable pressure matters

Pressure stability drives three things: operator comfort (no glove ballooning), air-quality stability (fewer O₂/H₂O spikes), and seal life (O-rings stop getting hammered). If your pressure swings, your ppm will, too.

  • Chamber overpressure: +3 to +8 mbar relative to ambient.
  • Relief valve (crack/open): +10–15 mbar. Test monthly.
  • Antechamber equalization: match chamber pressure within ±1 mbar before opening the inner door.
  • Negative pressure boxes (containment use): follow OEM limits; keep absolute stability, not “more negative is better.”

Plain truth: Running >+15 mbar all day just strains gloves and wastes gas without improving ppm.

10-minute tuning procedure

Record results (setpoint, flow, relief crack). Paste into your log.

Zero the reference: verify the ambient side of your transducer reads ~0 mbar.

Circulation on; regen off. You want a quiet box while tuning.

Set target: dial +5 mbar on the controller.

Trim make-up gas until the controller barely works—steady value, no hunting.

Check glove feel: hands in, move slowly. If the gloves “breathe” (push/pull), add a tiny bit of make-up flow or soften PID aggressiveness.

Pop-test the relief valve: gently over-pressurize; confirm it cracks ~+12 mbar, then reseats cleanly.

Antechamber discipline that protects pressure

  • Equalize first: after the last evacuate→backfill cycle, equalize to chamber pressure, then open the inner door.
  • Use the small chamber by default; large chambers cause bigger pressure steps.
  • Three vacuum cycles remove air with less pressure disturbance than long purge-only transfers.

Symptom → likely cause → fast fix

  • Glove ballooning / “breathing” → too high setpoint or aggressive PID → drop to +5 mbar; reduce controller gain; trim make-up flow.
  • Door “pops” when opening → antechamber not equalized → equalize to ±1 mbar before opening.
  • O₂/DP spikes after transfer → pressure swing + sloppy load-lock → fix equalization; enforce three-cycle SOP.
  • Relief valve hisses constantly → setpoint too close to crack pressure / valve contaminated → drop setpoint; clean/replace valve.
  • Reading drifts all day → transducer zero/ambient port blocked → clean line, re-zero, verify reference.

Maintenance that actually matters

  • Monthly: relief valve function test; clean any dust/condensate.
  • Quarterly: transducer zero/Span check; inspect tubing for kinks or solvent attack.
  • Any time after a move/service: re-tune setpoint, make-up flow, and equalization.
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