Vacuum, pressure fluctuations and thermal cycles: why they matter
Three factors most often missing from inquiries that damage glass and gaskets.
Short answer
Vacuum loads the glass in the opposite direction, pressure fluctuations act cyclically, thermal cycles create stresses in glass and gaskets. All three must be explicit in the input data.
No numeric vacuum or cycle limits are derived on this site: applicability is confirmed by the manufacturer of the assembly.
Vacuum
Glass and gaskets behave differently under excess pressure and under vacuum. A fitting suitable for 6 bar is not automatically suitable for full vacuum: this is a separate manufacturer confirmation.
Fluctuations and pulsations
Pulsating pressure accumulates fatigue in the glass and fasteners. For pulsating modes the manufacturer confirms applicability separately.
Thermal cycles and thermal shock
Borosilicate glass withstands thermal shock better than soda-lime glass but is not invulnerable: the rate of temperature change is limited. Gaskets age from cycles faster than glass.
- state the frequency and amplitude of cycles in the inquiry;
- consider washing and sterilization as separate thermal cycles;
- avoid direct contact of a cold medium with hot glass.