Vacuum Leaks - 2011-06

Real Vacuum Leaks   These leaks are penetrations or passages through the freeze dryer vessel or vacuum system: the chamber, the condenser if externally condensing, the vacuum lines, or the vacuum seals. A leak may be due to a single source, or multiple sources of smaller leaks.


Gross Leak
The leak is sufficient to prevent the vessel pressure from reaching values that are within the operating range of the vacuum gauges.

Operating Leak
The leak will allow the system to reach pressure within the operating range of the vacuum gauges. However, the ultimate pressure obtainable by the system is significantly higher than the specification for the lyophilizer.

Trivial Leak
The leak is small enough that the system can be pumped down to its low pressure specification. A trivial leak may be identified as a deviation from the normal rate-of-rise curve during the vacuum integrity test. Trivial leaks must be monitored closely as increasing deviations indicates degradation in the freeze dryer's vacuum tightness.

Virtual Vacuum Leaks

A virtual leak stems from a gas supply that is contained within the interior of the freeze dryer, not from a flaw in vessel integrity. A virtual leak may initially appear as either a trivial leak or an operating leak, although a leak rate high enough to qualify as a gross leak is possible.

Even when the virtual nature of this leak has been identified, it can still be a difficult task to determine the source and location of the outgassing. Virtual leaks are generally harder to find than real leaks because the source can be anywhere within the system's interior and can be as diverse as oils from a handprint, lint or other porous materials, mucilage from tape, or residual moisture.


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Tech Tips Home

These technical tips are for use by qualified maintenance personnel who are familiar with their specific freeze drying equipment. These tips are intended only as general guidelines. Lyophilization equipment is frequently custom configured and some tips may not be appropriate for all freeze dryers. Always read and follow the directions of your equipment's maintenance manual. If you would like to discuss one of our tech tips, please contact Dave Clayton at 215-672-7800 ext-1376.


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