Our lyophilizer will not pass the leak test with the thermocouples installed. Can your feedthrough solve this problem?
Yes and maybe no! Yes, if you use our feedthrough and thermocouples. Maybe no, if you use your existing thermocouples. A thorough analysis and understanding of the situation is required.
A leak rate test on a lyophilizer is a particularly difficult test even without the presence of thermocouples and a feedthrough. Our validation quality thermocouples will hold leak free for a leak test when new. Our feedthrough will leak test down to 10 microns of mercury. The combination in a properly made assembly will hold down to 10 microns of mercury. If we make and vacuum certify the assembly, it will pass vacuum leak test if your lyophilizer will pass the test without the assembly installed. No other company will even try to match this guarantee and still supply validation quality thermocouples. Why is this so?
Even new properly fabricated thermocouples can leak under high vacuum levels found in lyophilizers. During the process of extruding the outer jacket over the two conductors, the molten FEP or PFA can have non uniform melt properties that result in thin areas, fisheyes, and microscopic holes in the jacket. These defects leak under high vacuum. The only way to find them is to vacuum test each thermocouple. The other source of leaks is the feedthrough. Skyl-Tech, Inc is the only company that makes a feedthrough with a resilient sealant with oval holes containing a labyrinth “O” ring system in each hole. This gives a positive seal around the oval cross section of the thermocouple. All other feedthrough manufacturers use a “sandwich” seal of two flat sheets of rubber squeezed over the thermocouples placed between them. It is physically impossible to affect an acceptable vacuum tight seal in this configuration. It is also very difficult to get a good seal between the two rubber disks and the sensor wires without tightening the assembly until the jacket and conductor insulation on the thermocouple deforms and fractures leading to serious leaks in the thermocouple.
The sandwich flange cannot be used in high vacuum applications such as lyophilizers and definitely should not be used on Ethylene Oxide sterilizers where even leaks resulting in part-per-million concentrations outside the chamber cannot be tolerated. Some customers and fabricators will use low conformity grade solid conductor wire in an attempt to stop these leaks and accept the lower accuracy readings as the only solution.
Another consideration for lyophilizer and Ethylene Oxide applications is proper training for operational personnel and validation technicians. Any rough handling of the thermocouples can cause abrasions or cuts in the insulation, both visible and microscopic, which will result in leaks. Training must include a thorough understanding of the delicate nature of the thermocouples and the problems caused by the leaks.
September 9, 2009 at 10:23 am | Uncategorized | No comment