This had already been posted back in September 2007 and as it did attract tremendous interest I'm happy to give it a makeover with more detail ! 

For those who do not often change things on a UHV vacuum system, here's some tips if you need to mount a viewport. First, never use a viewport that appears to be, or is known to be damaged. A replacement viewport costs far less than repairing a system that has been subject of an implosion caused by a faulty viewport.
                                                                                           
SAFETY
Pressure differentials: Kodial VPZ viewports are designed to withstand 1 Bar differential pressure. Other standard viewports are designed to withstand 2 Bar differential pressure. The pressure on the ‘vacuum side’ of the viewport must not exceed a positive pressure differential of 1 bar. The viewports are designed for vacuum applications.

• WARNING: Pressures in excess of this or high reverse pressures may cause catastrophic failure and result in serious injury.

                                                                                                    

Mounting

• Viewport bolt-up procedure: Always use annealed copper gaskets and a washer with each bolt. Tighten opposing mounting bolts equally over several passes. Use a torque wrench to ensure equal sealing torque. Do not over tighten. Failure to follow this procedure will invalidate any warranty.

Handling

• WARNING: The optic surface is very delicate and will scratch easily. Always wear lint-free or surgical rubber gloves when handling. Never touch the optic surface.
• Storage: It is recommended best practice that all viewports are covered when not in use.
• Use: If the viewport is to be used in a vacuum system where materials are deposited or plasma cleaned, an internal viewport shutter should be fitted.
• Humidity: Anti-reflective coatings are durable and resistant to atmospheric moisture and other common contaminants

Cleaning

• WARNING: All viewports are supplied UHV clean and ready for use. Optical coatings are typically 10-300nm thick and as such are extremely delicate. Any materials deposited or removed from the coating will affect optical performance. Cleaning should only be attempted when absolutely essential.
• Dust: Dust should be removed using a particulate and water-free low pressure air-gun, aerosol or puffer.
• Light smudges (e.g. finger prints): Smudges should be removed by wiping very gently using a lint free optical quality wipe moistened with isopropanol (IPA). Do not use tissue paper.
• Other marks: Products with more serious marks and contamination should be returned to the supplier for cleaning and/or recoating.

Temperature Specs.
Baking: When baking, ensure the viewports are shielded from direct heat and strong temperature gradients, by, for example covering them with aluminium foil.

• Heating/ Cooling rates: Heating and cooling rates must be kept below 3 °C/min.
  Max Temperatures: Exceeding the temperatures bellow can invalidate warranty:

        

Viewport Type	|	Max Temp °C
Brazed Sapphire	|	450
Standard VPZ Kodial	|	350
Brazed Fused Silica	|	200
Brazed Quartz	|	200
Bonded	|	120
Mechanically sealed	|	130