Glove Box Pressure Control: Setpoints, PID Tuning & Relief Valve Basics

What “good” pressure control looks like

• Steady within ±0.5–1 mbar during normal work.
• Fast recovery (<10 s) after small glove movements.
• Quiet relief valve (no constant hiss).
• No “breathing” gloves while idle.

Recommended setpoints & alarms

• Setpoint: +5 mbar (start here, then adjust 3–8 mbar to fit your box).
• Low alarm: < +2 mbar (risk of inward leaks).
• High alarm: > +12 mbar (approaching relief crack).
• Equalization tolerance (antechamber): ±1 mbar before opening inner door.

Fast PID tune (practical, not textbook)

1. Start conservative: small P, zero I, zero D.
2. Increase P until you see slight overshoot on a step (e.g., opening/closing a purge valve), then back off 10–20%.
3. Add I slowly until the offset disappears within 10–20 s.
4. If you get oscillation after disturbances, add a touch of D (or reduce P).
5. Re-test with glove motions—that’s the real-world disturbance.

Rules of thumb

• Big box or long tubing → lower P, higher I time.
• High-flow controllers → lower P to avoid “pressure slap”.

Symptoms → likely causes → fixes

• Gloves “breathe” at idle → P too high or relief set too close → drop setpoint to +5 mbar, set relief +12 mbar.
• Hunting/oscillation → aggressive P/I or sticky valve → soften PID; check valve and filter for stiction.
• Slow to recover → flow restriction or I too low → check regulator/filters/tubing; increase I.
• Drift over hours → ambient swings or small leak → improve temperature stability; run leak test (pressure-decay).
• Constant relief hiss → setpoint near crack or backpressure → lower setpoint; reroute exhaust.

Relief valve basics (don’t skip)

• Crack test: ramp pressure slowly; note the mbar where flow starts (target +10–15 mbar).
• Seat check: after venting, ensure it reseats (no creeping loss).
• Quarterly: clean/filter upstream; record crack value in the log.

Quick 2-minute diagnostic (every Monday)

1. With the box idle, note pressure variance over 60 s (target ≤1 mbar).
2. Move gloves in/out twice; confirm return to setpoint <10 s.
3. Briefly raise setpoint by +1 mbar; ensure no relief hiss.
4. Log result next to O₂/DP.

Install & plumbing tips

• Keep the pressure line short and clean; avoid tiny or kinked tubes.
• Put a sintered filter ahead of proportional valves.
• Avoid routing pressure exhaust near sensor intakes (prevents false spikes).