PN6 External Hex Bolt Flange Sight Glass

The Borlan Fluid PN6 external hex bolt flange sight glass provides a direct observation point for tanks, vessels and process equipment. Its bolted circular construction uses external-hex fasteners for straightforward tool access during controlled assembly and maintenance. The 2025 Borlan catalog lists DN50 to DN150 sizes with 304 or 316L stainless-steel options.

PN6 is the catalog designation for this product family. It should not be treated as a universal operating guarantee for every size and configuration. Allowable working conditions depend on the complete assembly, including the glass, gasket, metal grade, fasteners, temperature, pressure or vacuum, process medium, installation and applicable project rules.

What Is a PN6 External Hex Bolt Flange Sight Glass?

A PN6 flange sight glass is a bolted observation assembly designed to provide visual access into a vessel or item of process equipment. A transparent circular window is retained and sealed between machined metal sections. The external-hex fasteners can be reached with common hand tools when the equipment has been safely isolated, drained, cooled and depressurized.

This construction differs from the recessed socket-head fastening used on the PN3 model, but the final choice should follow the equipment layout, maintenance preference, operating conditions and approved drawing. Buyers comparing flange, union, tubular, strip and fused products can use our industrial sight glass types guide.

Key Product Features

• External-hex bolted construction: the cover fasteners provide visible tool access for controlled assembly and planned service.
• Direct process observation: the circular window can support checks of liquid level, flow, foam, color and internal process condition.
• DN50-DN150 catalog range: six nominal sizes cover common vessel and equipment observation points.
• 304 or 316L stainless steel: both grades are listed as catalog options; confirm the exact grade and wetted-part scope in the order.
• Replaceable bolted assembly: glass and sealing components can be inspected or replaced under an approved maintenance procedure.
• Optional sight glass light: the catalog image shows an anti-corrosion light for reference. A light, power supply and related accessories are supplied only when stated in the quotation.
• Project-specific review: Borlan Fluid checks the medium, temperature, pressure, vacuum, cleaning method, installation interface and documentation before confirming supply.

Technical Specifications

Catalog Reference Dimensions

All dimensions are catalog references in millimeters. The available PN6 source sheets contain conflicting DN125 outside-diameter values, so D for DN125 must be confirmed on the latest approved production drawing. Confirm every dimension, the clear opening, glass thickness, gasket, fasteners and mounting interface before fabrication or installation.

External Hex Fasteners and Assembly Control

External-hex fasteners provide clear wrench access around the cover. This can simplify controlled tightening and removal where sufficient clearance is available. Their visible position also helps technicians include the fasteners in routine visual inspections. The assembly still requires the correct bolt grade, tightening sequence and loading procedure for the selected window and gasket.

Uneven tightening can concentrate stress in the glass or sealing system. Fasteners should be tightened progressively in a cross pattern, using the approved torque or assembly procedure. The mating surfaces must be clean, flat and aligned. Do not use the bolts to pull a distorted mounting flange into position, and do not allow nearby pipe strain or vessel deformation to load the window.

Material, Glass and Gasket Selection

The catalog lists 304 and 316L stainless steel. Selection should consider the process medium, cleaning chemicals, chloride exposure, corrosion risk and required documentation. State whether the material grade applies to all metal parts or only to wetted components. If the project requires material certificates, heat-number traceability or a particular surface finish, include those requirements in the inquiry.

Glass and gasket selection must be reviewed with equal care. Provide the normal and maximum process temperature, design and operating pressure, vacuum, cycling conditions, cleaning procedure and chemical exposure. The gasket must be compatible with the medium and stable across the expected temperature range. The window must be protected from impact, point loading, severe misalignment and uncontrolled thermal shock.

Optional Sight Glass Lighting

The product image in the Borlan catalog shows the PN6 sight glass with an anti-corrosion light. This image demonstrates an optional configured assembly and does not mean that a lamp is included with every PN6 sight glass. Lighting can improve visibility in closed or poorly illuminated vessels, but the lamp type, voltage, power, mounting method, cable arrangement, environment and power supply must be confirmed separately.

When requesting lighting, send the available voltage, AC or DC requirement, required wattage, installation environment and any enclosure or hazardous-area requirements. A general product photo must never be used as evidence of a certification or rating. Borlan Fluid will identify the confirmed light model and supply scope in the quotation.

Typical Applications

• Mixing and batching tanks
• Reactors, receivers and general process vessels
• Water-treatment and utility equipment
• Chemical processing equipment, subject to material compatibility
• Food, beverage and cosmetic equipment, subject to hygiene requirements
• Industrial equipment requiring a circular viewing window with external fastener access

These examples describe common application areas rather than guaranteed suitability. Hygienic service, corrosive media, vacuum, frequent cycling or rapid temperature change may require a different construction, seal, surface condition or documentation package. Our sanitary versus industrial sight glass guide explains additional selection points for clean-process systems.

Installation and Maintenance Guidance

1. Verify the product designation, nominal size, materials and approved drawing before installation.
2. Check that the mounting surface is flat, clean, aligned and free from damaging weld distortion.
3. Inspect the glass and gasket for chips, cracks, contamination, hardening or deformation.
4. Use the specified fasteners and tighten progressively in a controlled cross pattern.
5. Keep pipe strain, vessel distortion and unsupported external loads away from the sight glass.
6. Test and inspect the completed installation according to the approved equipment procedure.
7. Before maintenance, isolate, drain, cool and fully depressurize the equipment.

Inspection intervals should reflect the medium, operating temperature, pressure cycles, cleaning frequency and consequence of leakage. Replace any window that shows cracks, edge damage, deep scratches, clouding or other unacceptable deterioration. Use only approved replacement glass, gaskets and fasteners for the exact assembly.

Why Work with Borlan Fluid?

Borlan Fluid supplies conventional flange, union, pipeline and fused sight glass products, as well as sight glass lights and customized vessel accessories. For a PN6 inquiry, our team can review the equipment interface, viewing objective, material, glass, gasket, operating conditions, lighting and documentation before confirming the production scope.

For product demonstrations and factory updates, visit the Borlan Fluid YouTube channel and LinkedIn page. Match any video to the quoted size and configuration before using it as technical evidence.

Frequently Asked Questions

What does PN6 mean on this product page?

PN6 is the Borlan catalog designation for this flange sight glass family. Final allowable working conditions must be confirmed for the selected size, complete assembly, temperature, medium, pressure or vacuum and installation.

Why is it called an external hex bolt sight glass?

The cover uses fasteners with an external hexagonal head or nut that can be reached with a suitable wrench. This term distinguishes the construction from a recessed socket-head or internal-hex fastening style.

Which sizes are listed in the catalog?

The 2025 catalog lists DN50, DN65, DN80, DN100, DN125 and DN150.

Is the anti-corrosion light included?

No standard light inclusion should be assumed. The catalog image shows an optional anti-corrosion light configuration for reference. The lamp, voltage, wattage, cable, power supply and environmental requirements must be confirmed in the quotation.

Is the product available in 316L stainless steel?

Yes. The catalog lists 304 and 316L options. Confirm the exact material grade, wetted-part scope, surface requirement and documentation in the order.

What is the DN125 outside diameter?

The available source sheets contain conflicting DN125 values. Borlan Fluid will confirm the outside diameter on the approved project drawing before production.

What information is needed for a quotation?

Send the DN size, equipment or mounting drawing, medium, normal and maximum pressure, vacuum, minimum and maximum temperature, material grade, glass and gasket requirements, optional lighting, cleaning method, quantity, destination country and required inspection documents.

Request a Quote

Send Borlan Fluid your DN size, equipment or mounting drawing, medium, pressure or vacuum, temperature range, material grade, glass and gasket requirements, optional light requirements, cleaning method, quantity, destination country and documentation requirements. We will review the PN6 external hex bolt flange sight glass configuration and prepare a quotation based on the confirmed scope.