Sight Windows Information

Sight windows are an effective and economical way of viewing tank, pressure vessel, piping systems interiors, and/or vacuum environments.  They are also referred to as sight glass and are often replaceable or removable.  Fluid clarity, color, level, and flow can be monitored through the window.


Sight windows often include only the window without moving parts.  The shape of the window is round or oblong.  They can be mounted by bolting, welding, or direct insertion into the end of a pipe or tank.  Welding may require a radius pad that conforms to the pipe or curved vessels or a flat pad that mounts to a flat tank wall.  Sight windows can also consist of a small housing with a flange or thread for direct insertion.  Dimensions of the sight window and/or complete housing can be specified.

Window Material and Seal Material

Window material and seal material may be important based upon application.  Borosilicate, also known as Pyrex®, includes very good chemical durability and a low thermal expansion coefficient.  Glass, plastic or acrylic, or other materials may be chosen based upon the glass to metal bonding and vacuum requirements.  Ultraviolet (UV) grade materials may also be specified.  Viton seals are often chosen for high temperatures.


Features may include single or dual window.  Dual windows, two glass discs held in position by a metallic housing, internal shims and gaskets, provide added protection in applications where there is external mechanical impact, high pressure or corrosion/erosion. FM Approval, FDA, or other approval may be necessary in food, dairy, and pharmaceutical applications.  American National Institute of Standards (ANSI) ratings for safety in high-pressure environments may also be required.


Wipers are included to clean the viewing area of the sight window.  Wipers remove condensation and debris from the inside of the sight glass.  They are often used with high viscous fluids and/or suspended solids.


Observation of the contents of a pipeline, tank or pressurized vessels and other process equipment may be necessary for quality control and/or visual inspection. 


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