360-DEGREE VIEW: This type of flow indicator passes fluid through a glass cylinder that is visible from all sides. This allows ample ambient light to illuminate the flow. For protection, the tube is mounted inside an enclosure of clear plastic.

ANNEALING: Hot glass is slowly cooled to prevent buildup of internal stresses. This allows the glass to be cut and otherwise processed afterward. Annealing is commonly used in the production of ordinary glass. Further strength improvement can be accomplished by toughening or tempering the glass.

ASME-BPE: The ASME-BPE (Bio-Processing Equipment) Standard is a specification for the design, manufacture and acceptance of vessels, piping and related accessories for use in equipment used in the biopharmaceutical industry. Sanitary sight glasses should meet ASME-BPE standards at a minimum.

BOROSILICATE: A formula of glass used in some sight ports. According to the Glass Engineering Handbook (McGraw-Hill, 1984), borosilicate glass contains 11 percent boric oxide. Boric oxide gives borosilicate glass superior performance to soda lime glass in terms of temperature, thermal shock and chemical resistance.

CHEMICAL RESISTANCE: It is important to consider the effect of chemicals on the sight glass over time. Common glass is not chemically inert and will react even with water. Laboratory-grade glass (borosilicate glass) is relatively inert except to hydrofluoric acid, hot phosphoric acid, and hot alkalis.

CORROSION: Acidic or caustic process fluids may cause corrosion of the glass in a sight-flow indicator, noticeable as a cloudiness that limits transparency. Borosilicate glass is more corrosion-resistant than soda lime glass.

HEAT TREATING: Annealed glass may be subjected to additional heat treating to further increase its strength. Glass is heated to approximately 680 C, almost its softening point. It is then quenched or cooled with a steady high-pressure flow of compressed air. This process quickly cools the surfaces that go into compression while the core (inside) is allowed to cool more slowly and goes into tension. This process makes heat-tempered glass three to five times as strong as annealed glass.

HYGIENIC CLAMP: A fitting consisting of two neutered ferrules having flat faces with a concentric groove and mating gasket that is secured with a clamp, providing a nonprotruding, recessless product contact surface (per ASME-BPA).
HYGIENIC: Equipment and piping systems that by design, materials and operation provide for the maintenance of cleanliness so that products produced by these systems will not adversely affect health (per ASME-BPA).

METAL JACKET: Mounts over a sight-flow indicator to allow steam to circulate around it. It allows direct observation of high-temperature or temperature-sensitive process fluids without creating a cold spot on temperature-controlled process piping, by exposing only the small area of the indicator’s viewing port to ambient temperature.

MONITOR: To keep an eye on a process over time. Sight ports may be fitted with video cameras that allow remote monitoring as well as recording.

MOUNTING LIGHTS: Lights for sight-glass application use different mounting configurations, from a “half-moon” type designed to fit a weld-on sight port to the latest sleek sanitary design where the light fits directly into a sanitary fitting for one-piece mounting right onto the ferrule. For existing sight ports, some lights are made to mount easily onto the cover flange.

OBSERVE: To see what is happening to a process. The ability to see what is happening inside a pipe can be invaluable to process operators. Despite technological advances, no sensor can equal the human eye and its more than 94 million photo receptors.

SIGHT INDICATOR: A device installed on a pipe to provide a visual means of verifying liquid flow for direction and approximate rate. Simple and low-cost, it also allows operators to observe the color and clarity of process fluids through a window.

VIEW-THROUGH: This type of flow indicator has two sight ports arranged in parallel so that an operator can see the intervening flow of fluid lighted from behind. This design is suited for pressurized, high temperature, and harsh fluid applications.

The terms and definitions for this word search were provided by LJ Star, a manufacturer of sight glass, sanitary fittings, and non-ex lights for process observation.