Installation and Maintenance Tips


Never re-use glass or gaskets.

  • Once a conventional sight glass has been removed from its mounting, regardless of the reason for removal, discard the glass and gaskets and substitute new glass and gaskets. Exception: Metaglas® safety windows may be reinstalled, following instructions provided for this procedure.
  • Keep glass clean using commercial glass cleaners.
  • Never use wire brushes, metal scrapers or harsh abrasives.
  • Do not attempt to clean glass while equipment is in operation.


Sight glasses should be regularly inspected for damage.

  • To examine for scratches, shine a very bright concentrated light source at an angle of about 45°. Anything that glistens should be inspected closely.
  • Scratches that catch the fingernail and any star or crescent-shaped marks that glisten are cause for replacement.
  • Sight glasses that appear cloudy or roughened after cleaning should be replaced.
  • Also inspect sight glass frames/flanges for corrosion buildup.


Never use damaged glass.

  • Never use glass that is scratched, chipped or otherwise damaged.
  • Glass seating surfaces must be flat within 0.005˝ with a smooth finish.
  • Flanges must be rigid.
  • Do not allow the glass to contact metal when assembling.
  • Gaskets must be new, clean and smooth.
  • Use gaskets of the same diameter and fit them concentrically.


Never tighten bolts on a sight glass while equipment is in operation.

  • Follow a regular tightening sequence to ensure even loading of glass.
  • Allow a maximum difference of 1.5 ft/lbs between bolts during tightening.
  • Tighten only enough to produce a positive seal against the process pressure.
  • Bolts may need tightening after initial cycling of vessel.
  • Never tighten bolts when the sight glass is hot.

L.J. Star Incorporated • (330) 405-3040 •