Viewport Safety

The risks of damage to UHV viewports are due to the inherent fragility of the window materials. Risks for window failure include impact, scratches, thermal shock, over-pressurization, or excessive mechanical stress.

Impact

When a viewport is not in use, protecting it from impact with a transparent polycarbonate safety cover or anodized aluminum bake-out cap will reduce the risk of vacuum implosion and concomitant damage to equipment or injury to personnel.

Scratches

Covering the window will also keep it free from abrasive dust that could then result in scratching a viewport during cleaning. Calcium fluoride, magnesium fluoride, and zinc selenide are easily scratched. Scratches can lead to viewport failure. Do not allow window surfaces to contact abrasive, sharp, or hard materials. A transparent polycarbonate safety cover or anodized aluminum bake-out cap can protect against inadvertent contact. Follow recommended cleaning procedures to avoid scratching the unprotected window surfaces.

Thermal Shock

Viewports should never be exposed to a thermal gradient of more than 10 degrees C per minute. The maximum bakeout temperature for extended range UHV viewports is 200°C. During heating, the transparent polycarbonate safety cover should be removed. This cover can be replaced with an anodized aluminum bake-out cap to maintain a uniform window temperature.

Over-pressurization

Viewports as configured are rated for ultrahigh vacuum service with a maximum differential pressure of 15 psi. Replace any visibly damaged viewport, do not use it and risk window failure.

Excessive mechanical stress

It is highly recommended that extended range UHV viewports be installed using fully annealed OFE copper gaskets. When mounting a Conflat flanged viewport the bolts should be tightened in a “star” or “crisscross” pattern gradually. It is helpful to use a calibrated torque wrench to ensure uniformity of the clamping torque.