Tank Sight Glass type 121-D | Noris

Tank Sight Glass Noris Type 121-D

The Noris Type 121-D is a circular sight glass conforming to DIN 28121, designed for installation on existing DIN flanges. The 121-D variant differs from Type 121 by incorporating a dual safety window arrangement: each borosilicate glass disc is rated for full design pressure, ensuring that in the event of one disc failure, the secondary barrier remains intact, maintaining containment integrity.

Operating Conditions

• Operating pressure: 10 bar or 25 bar
• Operating temperature: 150 °C or 200 °C
• Standard: DIN 28121
• Connection: flanged, compatible with existing DIN flanges
• Sealing: O-ring system between flanges
• Optional certification: EN 10204-2.2 or EN 10204-3.1

Materials and Construction

Materials and dimensions refer to the Bauform 121 datasheet. For Type 121, body and cover are available in carbon steel or stainless steel 1.4571, borosilicate glass per DIN 7080, and PTFE enveloped gasket rated up to 200 °C. Sizes cover DN 40 to DN 200 for 10 or 25 bar pressure classes.

Typical Applications

• Tanks, boilers, and silos with flanged inspection ports
• Visual inspection of level, foaming, color, or medium clarity
• Installations requiring an additional secondary glass barrier
• Processes requiring local illumination or internal vessel observation

Options

Available options include special flange finishes, anti-fog heating elements, lined base flanges, sight glass luminaires, ANSI connections, and custom designs for temperatures above 200 °C.

Selection Criteria

Type 121-D is selected when risk assessment requires dual glass protection versus the single barrier of Type 121. Final selection should verify design pressure, temperature, O-ring compatibility with process media, flange material, and required material certification.

FAQ

Is an actuator required?
No. This is a static visual inspection device.

When is it preferred over Type 121?
When dual safety windows are required to limit leakage in the event of a single glass disc failure.

What is checked during maintenance?
Condition of glass discs, O-ring, seating surfaces, bolts, tightening torque, and evidence of leakage at the flanged connection.