Electrical Breaks - Introduction
Electrical Break is the classification given to ISI™ vacuum components consisting of metal tube hardware brazed to either end of a ceramic tube. Components with diameters below 2.5 inches are referred to as Breaks and those with diameters above 2.5 inches are referred to as Envelopes.
The metal tubes provide a means of attaching these electrical breaks to other vacuum components such as flanges and chambers. The central ceramic portion provides electrical insulation between the conductive metal ends. In other words, the ceramic produces an Electrical Break in an otherwise continuous tube geometry.
MDC offers three ISI™ Break designs for service within Cryogenic, Liquid and Vacuum environments:
Cryogenic Breaks are used in the transmission of cryogenic fluids to provide an electrical break in the transmission line. These Breaks are suitable for service down to liquid nitrogen temperatures (-200°C). Although rated for cryogenic service, thermal gradients of 25°C per minute must be observed to preserve the life of the seal. These breaks are designed with thin metal transitions that provide flexibility at sub-zero temperatures. They are not suitable for line pressures in excess of 15 PSI pressure differential. Cryogenic Breaks can be installed by the Tungsten Inert Gas (TIG) welding process.
Liquid Breaks are used for the transmission of coolant fluids to provide an Electrical Break in the transmission line. Service temperature for these Breaks is restricted by coolant temperature limits. Thermal gradients of 25°C per minute must also be observed with these products. These parts are rated for a maximum line pressure of 75 PSIG. Liquid Breaks are typically installed by soldering or low-temperature brazing. Note that subsequent brazing temperatures must not exceed 700°C.
Vacuum Breaks and Envelopes are used in vacuum transmission lines to provide an electrical break in the transmission line. Note again that thermal gradients of 25°C per minute must be observed to preserve the life of the seal. Weldable vacuum Breaks and Envelopes are typically installed using any of three fusing processes - Laser, Electron-Beam or TIG welding.
ISI™ Electrical Breaks and Envelopes are all suitable for service in ultra high vacuum environments. Cryogenic and Vacuum Breaks are not suitable for water service because of hardware corrosion. Liquid and Vacuum Breaks are not suitable for cryogenic service because of expansion differential and hardware embrittlement at liquid nitrogen temperatures. All Breaks and Envelopes are bakeable to 450°C for short term vacuum conditioning. Long term high temperature service is not recommended because of corrosion to metal hardware components.
Intended Operating Conditions
Electrical ratings are safe operating limits. These ratings are determined by various factors, including dielectric strength, geometry and system operating pressure. Please note that all ISI™ catalog products are electrically rated for operation with one side in dry atmospheric conditions and the other side in a vacuum environment with a maximum system pressure of 1 x 10-4 Torr. We advise that users make allowances for deviations from stated operating parameters and take adequate safety precautions when feedthroughs are operated at high voltages or high currents.
Insulator Seal (ISI) brand catalog and custom engineered ceramic to metal seal products are manufactured to ISO 9001:2008 standard utilizing our qualified hermetic brazing and joining processes.