NPT Sight Glass

NPT sight glasses are typical NPT fittings having NPT male threads, where the window is encased into the metal housing forming a single-piece part.

Designed up to 7000 psi pressure, these sight glasses have optical clarity suitable for imaging systems and also for looking at oil levels inside pressure vessels, or checking the color of a refrigerant. These NPT sight glasses transmit a broad spectrum of wavelengths, ranging from near-infrared, visible light, to ultraviolet. Sight glasses with quartz use material GE-124 quartz. It's a pure form of silica commonly used in semiconductor equipment. This quartz has high purity for use in a process in semiconductor reactors.

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This is the full technical specification: http://quartz.com/gedata.html UV cutoff is at < 160 nm. Encole also manufactures custom sight glasses with higher optical properties, using Suprasil 311 or Corning 7980.