A sight glass (also known as a sight glass, observation glass, or sight cup) is a device used on industrial pipelines or containers to directly observe the flow, color, state, or liquid level of internal media. According to different application requirements, structural characteristics, and medium conditions, there are multiple classification methods for mirrors. The following is a detailed list of types of mirrors:
一 、 Classified by structure and function
1， Straight through sight glass (circular sight glass, pipeline sight glass)
Structure: Flanged at both ends, directly installed between the pipeline flanges. The middle is composed of a window glass (lens) and a pressing structure.
Usage: Most commonly used for observing the flow of liquids, gases, or vapors in pipelines (such as flow, bubbles, color, turbidity).
Common types:
Floating ball sight glass: There is a floating ball inside the sight glass cavity, and the flow rate or direction can be roughly determined based on the position of the floating ball.
Impeller sight glass: There is a small impeller inside the sight glass cavity, and the flowing medium will push the impeller to rotate, which intuitively displays whether the fluid is flowing and the approximate flow velocity.
2、 Flange style mirror (flat mirror, neck mirror)
Structure: It comes with a short section (neck) and flange, which can be directly connected to the flange of equipment or pipelines. Usually, larger lens sizes provide a better viewing field.
Usage: Commonly used on the side or top of equipment such as reactors, tanks, and towers to observe internal reaction conditions, material status, or liquid levels.
3. Glass level gauge (level sight glass)
Structure: This is a sight glass specifically designed to display liquid levels. It usually consists of two valves, one upper and one lower, and one or more columns (observation tubes) with glass plates in the middle.
Type:
Glass tube level gauge: simple structure, low cost, but weak pressure and temperature resistance.
Dual color liquid level gauge: Based on optical principles, the gas phase displays red and the liquid phase displays green (or other contrasting colors), especially used on steam boilers, which is very clear for night or long-distance observation.
Frost proof level gauge: used for low-temperature media (such as liquid ammonia), with frost proof devices on the surface of the window to prevent ice and frost from affecting observation.
Illuminated liquid level gauge: Equipped with LED or other light sources for easy observation in low light environments.
4. Peek lamp (with light mirror, illumination mirror)
Structure: Integrated or equipped with lighting sources (usually explosion-proof LED lights) on the basis of standard mirrors.
Usage: Used in situations with dim lighting or where clear observation of internal details is required (such as catalytic reactions, crystal growth, fermentation processes). Commonly found in biological fermentation tanks, pharmaceutical reaction vessels, etc.
5. Sanitary grade mirror
Structure: Using quick release clamps (such as SMS, DIN, ISO standards) or threaded connections, the contact area between the lens and the medium is smooth and free of dead corners, making it easy to disassemble, clean, and sterilize (CIP/SIP).
Material: Usually 316L stainless steel, with high borosilicate glass or sapphire glass lenses.
Purpose: Specially designed for industries with high hygiene requirements such as food, beverage, dairy, pharmaceutical, biotechnology, etc.
