Round sight glass with a pre-drilled hole allows operators to visually inspect fluid flow, verify liquid levels, and monitor process conditions without opening the pipeline or vessel. Also known as drilled sight glass, pre-drilled round viewport, or circular observation window with hole, this component integrates seamlessly into industrial piping systems where real-time visual access is required.
Applications
The round sight glass with hole is widely used across multiple industries for direct visual monitoring of internal processes:
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Pipeline flow inspection – Confirm fluid movement and detect flow interruptions in real time
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Tank & vessel level monitoring – Observe liquid levels inside storage tanks, reactors, and silos
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Oil & hydraulic system surveillance – Monitor lubricating oil levels, color changes, and contamination in gearboxes and rotating equipment
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Pharmaceutical & food processing – Verify CIP/SIP operations and product flow in sanitary lines
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Chemical processing – Inspect aggressive media through chemically resistant borosilicate glass in reactors and mixing vessels
Material & Specifications
Sight Glass Plate
| Item | Specification |
|---|---|
| Material | Borosilicate glass (DIN7080) / Soda-lime glass (DIN8903) / Quartz glass |
| Operating Temperature | Up to 280°C (borosilicate) / Up to 900°C (quartz) |
| Max Pressure Rating | Up to 20 barg (flanged), up to 10 barg (threaded) |
| Viewing Diameter | 25 mm – 200 mm (customizable) |
| Drilling Options | Pre-drilled through hole / blind hole / countersunk hole — diameter & position customizable |
Body & Mounting
| Component | Available Options |
|---|---|
| Body Material | SS304 / SS316L / Carbon steel |
| Gasket Material | PTFE / Viton® / NBR / Silicone rubber |
| Connection Type | Threaded (NPT / BSP / Metric), Flanged (ASME B16.5 / DIN), Weld-end |
| Standards Compliance | DIN 7080 (borosilicate glass), DIN 28120 / DIN 28121 (circular sight glass fittings), ASME B16.5 |
Technical Specifications
| Parameter | Value / Range |
|---|---|
| Product Type | Round sight glass with hole / Pre-drilled circular viewport |
| Diameter | 25 mm – 200 mm |
| Viewing Diameter (clear aperture) | 20 mm – 150 mm |
| Hole Diameter (pre-drilled) | 2 mm – 30 mm (customizable upon request) |
| Thickness | 6.5 mm – 25 mm (depending on pressure rating) |
| Material | Borosilicate (DIN7080) / Soda-lime (DIN8903) / Quartz |
| Pressure Rating | PN 16 / PN 25 / PN 40 / Class 150 / Class 300 |
| Temperature Range | -20°C to 280°C (borosilicate) / up to 900°C (quartz) |
| Connection Types | Threaded (NPT / BSP / Metric), Flanged (ASME / DIN), Weld-end |
| Gasket Materials | PTFE, Viton®, NBR, Silicone, Mica (high-temp) |
| Standards | DIN7080, DIN28120, DIN28121, ASME B16.5, ISO9001 |
Common Sizes (Pre-drilled round sight glass with hole)
| Nominal Size DN | Glass Disc Diameter (mm) | Viewing Diameter (mm) | Standard Hole Diameter (mm) |
|---|---|---|---|
| DN 25 | 50 | 30 | 4 |
| DN 40 | 80 | 48 | 6 |
| DN 50 | 100 | 65 | 8 |
| DN 65 | 120 | 80 | 10 |
| DN 80 | 150 | 100 | 12 |
| DN 100 | 180 | 125 | 14 |
| DN 150 | 250 | 180 | 18 |
Custom hole sizes and positions available. Please contact us for non-standard requirements.
Key Advantages
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Pre-drilled for convenience – Ready-to-install with factory-machined holes, eliminating on-site drilling risks and ensuring precision
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High-temperature resistance – Borosilicate glass withstands up to 280°C; quartz glass option handles up to 900°C for extreme thermal applications
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High-pressure compatibility – Rated up to Class 300 / PN 40 for demanding industrial environments
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Superior chemical resistance – Borosilicate glass resists acids, alkalis, water vapor, and most aggressive chemicals
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Crystal-clear visibility – High optical clarity enables accurate fluid color, clarity, and contamination monitoring
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Multiple connection options – Choose from threaded (NPT/BSP), flanged (ASME/DIN), or weld-end configurations to suit any piping system
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Full traceability – Each glass disc complies with DIN7080 standards; certificates available upon request
Certifications & Quality Assurance
Our round sight glass with hole is manufactured under strict quality controls and complies with:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality management system certified |
| DIN 7080 | Thermally toughened borosilicate sight glass plates |
| DIN 28120 / DIN 28121 | Circular sight glass fittings for pressure vessels |
| ASME B16.5 | Flange dimensions for ANSI/ASME mounting |
| EN 10204 3.1 | Material inspection certificate available upon request |
Third-party inspection reports and material test certificates are available upon request.
Evidence & Case Examples
Laboratory Test Data – Independent pressure testing confirms that borosilicate glass discs withstand up to 6 MPa at 260°C without cracking, with all tested samples meeting DIN7080 bubble and impurity tolerance specifications (≤3 air bubbles of ≤0.5mm per 10mm×10mm area, zero cracks or visible defects)
Field Case: Chemical Plant – A major chemical facility replaced conventional flat sight glasses with pre-drilled round sight glasses featuring PTFE-coated gaskets and borosilicate glass. After 18 months of continuous operation handling aggressive acid media at 200°C and 12 barg pressure, all units remained leak-free with zero glass degradation.
Installation Reference: Food & Beverage Processing – A dairy processing line installed our drilled sight glasses on CIP return lines. Operators reported 100% visibility of cleaning solution flow throughout all cycles, eliminating the need for line disassembly for visual confirmation and reducing maintenance downtime by 40%.
Images and full test reports available upon request. Contact us for a copy of our inspection documentation.
Why Choose Our Round Sight Glass with Hole?
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Factory-pre-drilled to your exact specifications – no secondary machining required
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Traceable materials with full certification package
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Fast lead times for both standard and custom sizes
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Technical support for flange/thread matching and installation guidance
