Tempered soda-lime sight glass is generally recommended for continuous service temperatures up to 150°C. The permitted working pressure cannot be determined by glass material alone. It depends on the disc diameter, thickness, unsupported viewing diameter, mounting design, gasket, bolt load, operating temperature and applicable safety standard. Every pressure application should therefore be evaluated according to the complete sight-glass assembly.

For temperatures above 150°C, significant thermal cycling or aggressive chemical service, borosilicate, aluminosilicate or quartz glass should be considered instead.

Key Features and Advantages

Economical material: A cost-effective solution for general industrial observation.

Clear visibility: Ground and polished surfaces provide reliable visual inspection.

Tempered construction: Improved mechanical strength compared with ordinary annealed glass.

Standard compliance: Available according to DIN 8902 or BS 3463 requirements.

Flexible production: Standard diameters, custom dimensions and optional holes are available.

Easy replacement: Suitable for many circular sight-glass holders and viewing assemblies.

Technical Specifications

Sizes

Soda-lime sight glass discs can be manufactured in a wide range of standard and custom dimensions. Typical manufacturing capability includes:

Diameter: approximately 10–420 mm

Thickness: approximately 1–19 mm

Options: plain disc, centre hole, mounting holes or custom profile

Edges: ground, polished, chamfered or otherwise finished as required

Common DIN 8902 replacement discs are available for industrial sight-glass assemblies. Custom diameters and thicknesses can also be produced according to drawings, samples or the dimensions of the existing glass.

Frequently Asked Questions (FAQ)

Q: When should I choose soda-lime sight glass?

A: Soda-lime sight glass is a suitable choice when:

The operating temperature does not exceed 150°C

The process has no rapid temperature changes or severe thermal shock

The medium is non-aggressive or only mildly corrosive

Clear visual observation is required

The application involves low to moderate pressure

A reliable and cost-effective viewing solution is preferred

Q: What information is required for a quotation?

A: Please provide the following information:

Material

Outside diameter

Thickness

Quantity

Operating temperature

Operating pressure

Process medium

Hole size and position, if required

Drawing or sample, if available

Q: What is the difference between borosilicate, aluminosilicate, quartz and soda-lime sight glass?

A: The main differences are operating temperature, pressure capability, thermal shock resistance and cost.

Soda-lime sight glass is an economical option for general, low-temperature observation applications. Its typical operating temperature is up to approximately 150°C, and it is primarily used in low-pressure systems.

Borosilicate sight glass offers good chemical resistance and thermal shock resistance. It is suitable for most industrial tanks, pipelines and process equipment, with a typical operating temperature of up to 280–300°C. Specially designed assemblies may withstand pressures up to 200 bar.

Aluminosilicate sight glass provides higher mechanical strength and is suitable for elevated-temperature and high-pressure applications. Its typical maximum operating temperature is approximately 375°C. Properly designed assemblies may operate at pressures up to 225 bar.

Quartz sight glass provides excellent high-temperature and thermal shock resistance, with a typical operating temperature of up to 1,000–1,100°C. It is commonly used in furnaces, reactors and thermal-processing equipment. However, quartz does not automatically provide the highest pressure resistance.

All pressure values are for reference only. Actual allowable pressure depends on the glass diameter, thickness, edge finish, mounting assembly, gasket, operating temperature and required safety factor.