Valves for Vacuum Service Service
Vacuum service encompasses any application where the process pressure is below atmospheric (0.1–101 kPa absolute). Common vacuum applications include distillation columns (crude vacuum unit), ejector/vacuum pump suction, pharmaceutical lyophilisation (freeze-drying), semiconductor process chambers, paper machine forming sections, and industrial furnaces. The key valve challenge is that the pressure differential acts in the reverse direction — atmospheric pressure acts to collapse thin-wall structures and to pull stem packing inward rather than push it outward, requiring different seat and packing design considerations.
Pressure Range
0.001–101 kPa absolute (deep vacuum to near-atmospheric)
Temperature
Ambient (pharma freeze-drying) to 420°C (refinery crude vacuum unit)
Industries
Refinery crude vacuum unit, Pharmaceutical (lyophilisation), Chemical distillation
Key Properties — Vacuum Service
- Pressure below atmospheric — 1 mbar to 100 kPa absolute
- External (atmospheric) pressure greater than internal — reverse pressure loading on seats
- Packing leakage draws air in (rather than fluid out) — atmospheric oxygen ingress hazard in hydrocarbon vacuum service
- Crude vacuum unit: 5–40 mmHgA at 350–420°C — high temperature + deep vacuum
- Pharmaceutical lyophilisation: 0.1–1 mbar absolute
Material Compatibility — Vacuum Service
Ratings are indicative. Actual compatibility depends on concentration, temperature, velocity, and presence of contaminants. Always consult corrosion tables or a materials engineer.
| Material | Rating | Notes |
|---|---|---|
| Carbon Steel (WCB) | Excellent | Standard for high-temperature refinery vacuum service. |
| A217 WC6/WC9 (Cr-Mo) | Excellent | For crude vacuum unit above 400°C. |
| SS 316L | Excellent | For pharmaceutical and clean vacuum service. |
| Graphite packing | Excellent | Preferred packing for vacuum valves — maintains seal under reverse differential pressure. |
Recommended Valves
Gate Valve (OS&Y, pressure-seal bonnet for high-temp vacuum)
Mainline isolation on crude vacuum column overhead and bottoms
Globe Valve
Control service in refinery vacuum unit transfer line
Butterfly Valve (large-bore, high-performance)
Low-pressure vacuum duct isolation in ejector systems and paper machine
Ball Valve (SS 316L, PTFE seat)
Pharmaceutical vacuum service — tight shutoff required, zero external leakage
Safety Vacuum Relief Valve (vacuum breaker)
Prevention of vessel collapse on loss of vacuum — admits air to break vacuum safely
Valves to Avoid
Wafer-pattern valves without bolted support in full vacuum — face gaskets may be pulled inward
Butterfly valves with rubber liners for deep vacuum — liner collapses
Special Considerations
Applicable Standards
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