Controlled leakage device for chamber contg. pressurised gas - using cracked glass disk, or tube contg. cracked glass bead, esp. to obtain gas stream for calibrating leakage detectors

摘要

The device consists of a flat piece of glass contg. several cracks; and at least some of the cracks extend through the entire thickness of the piece so they form a leakage path for a gas. The cracks are pref. located in the central zone of a flat glass disk; and can be made by local heating of the central zone of the disk and then quenching. An alternative pref. device consists of a tube made of glass or vitreous silica. A glass bead is welded in the bore of the tube; and the bead contains through cracks forming a leakage path for the gas. The cracked bead can be made by melting the end of a glass rod in the bore of a tube. The rod has a higher coefft. of thermal expansion than the tube, so the bead cracks on cooling. Used for example, to obtain a slight leakage of helium employed to calibrate He leak detectors.