BL-SJFL-XX Fused Flat Flange Sight Glass

The Borlan Fluid BL-SJFL-XX fused flat flange sight glass combines a stainless-steel flange with a fused glass-to-metal observation window. It is designed for bolted installation on tanks, vessels and process equipment where a compact circular viewing point and a flatter process-contact surface are required. Catalog sizes cover DN50 to DN200 with PN16 flange dimensions.

In the model code, XX represents the selected nominal size. The flange designation, dimensions and bolt pattern must match the mating equipment. Pressure, vacuum, temperature, medium, thermal cycle, metal grade, sealing arrangement and documentation must be confirmed for the exact configuration before quotation and fabrication.

What Is the BL-SJFL-XX Fused Flat Flange Sight Glass?

The BL-SJFL-XX is a bolted flat flange observation window from the Borlan Fluid fused sight glass range. In this construction, the transparent window and stainless-steel supporting section are fused into a compact assembly. The catalog describes the fused series as providing a flush surface with fewer steps and crevices than a conventional multi-part retained window.

“Fused” describes the glass-to-metal construction, while “flat flange” describes the bolted mounting form. It does not mean that every fused sight glass has the same flange dimensions or operating limits. Buyers should compare the complete drawing, bolt circle, hole diameter, flange thickness, clear opening and mating seal. Our industrial sight glass types guide explains why window construction and connection type must be specified separately.

Key Features

• Fused glass-to-metal structure: the window and stainless-steel support form a compact observation component.
• Flat flange mounting: the assembly connects through a defined bolt pattern to a matching vessel or equipment interface.
• Flush process-side geometry: designed to reduce internal steps and simplify the contact surface compared with conventional retained-window assemblies.
• DN50-DN200 catalog range: seven standard dimensional rows support different viewing and installation requirements.
• PN16 catalog flange dimensions: the catalog identifies PN16 geometry; allowable working pressure remains configuration- and service-specific.
• O-ring dimensions listed by size: each catalog row provides a reference O-ring dimension for interface checking.
• Project-specific confirmation: metal grade, glass, seal, pressure, vacuum, temperature, surface finish and documentation are reviewed before production.

Technical Specifications

Catalog Reference Dimensions

All dimensions are in millimeters and follow the labels shown on the catalog drawing. PN16 identifies the catalog flange dimensional series; it must not be used alone as proof of the allowable working pressure of every completed assembly. Confirm the approved drawing, mating flange, fasteners, seal and operating conditions before machining or installation.

Why Use a Fused Window in a Flat Flange?

A conventional bolted sight glass may use a separate window, multiple gaskets and a retaining cover. A fused window integrates the glass-to-metal section into a more compact component. This can reduce the number of internal interfaces and provide a smoother process-contact geometry, which may help where cleanability, limited installation height or a compact viewing point matters.

The construction still requires correct engineering. The fused joint does not remove the need to confirm pressure, vacuum, thermal expansion, flange flatness, gasket hardness, bolt loading and the structural capacity of the mating equipment. For a side-by-side explanation, see fused versus conventional bolted sight glass.

Understanding the PN16 Catalog Designation

The dimension table lists PN16 beside each size. On this page, PN16 identifies the flange geometry used in the Borlan catalog table, including outside diameter, bolt circle, thickness, hole diameter and hole count. It does not replace an engineering review of the complete observation assembly.

Allowable working pressure depends on the exact glass-to-metal construction, size, material, temperature, vacuum condition, cyclic loading, mating flange, gasket, fasteners and applicable design rules. State normal pressure, maximum or design pressure, test pressure, vacuum and pressure cycling in the inquiry. If a project requires a certified rating or inspection document, identify that requirement before quotation.

Thermal Cycling and Soft-Seal Requirements

The Borlan catalog instructs users of the fused sight glass series to limit heating and cooling to 2-3°C per minute and to use a soft seal at the contact face. These are operating constraints, not optional marketing features. Rapid temperature change can create thermal gradients and stress even when the normal process temperature is within the material range.

Include startup, shutdown, hot-water cleaning, steam exposure, cold rinsing, outdoor temperature, insulation and abnormal events in the thermal review. Do not direct a cold cleaning stream onto a hot window or expose a cold window suddenly to a hot medium. Read our sight glass thermal shock guide for the information needed to evaluate temperature transitions.

Seal, Mating Flange and Bolt Installation

The supplied or selected soft seal must be compatible with the process medium, cleaning chemicals, minimum and maximum temperature and required documentation. A seal that is too hard, incorrectly sized or unevenly compressed can introduce point loading or leakage. The catalog provides reference O-ring dimensions, but the approved order drawing and confirmed seal material govern production and installation.

The mating flange should be flat, clean and aligned. Verify the outside diameter D, bolt circle K, flange thickness S, drawing diameters d1 and d2, hole diameter d3 and number of holes. Tighten fasteners gradually in a cross pattern using the project-approved procedure. Uneven tightening, pipe strain or forcing mismatched bolt holes into alignment can load the fused window.

Material and Surface Requirements

The catalog identifies a stainless-steel and glass fused construction but does not assign one metal grade to every BL-SJFL-XX configuration. Specify the required body and wetted metal grade, process medium, chloride exposure, cleaning chemicals and material documentation. Do not assume that every stainless-steel grade is suitable for every product or cleaning cycle.

If the application has hygienic requirements, state the required wetted-surface finish, inspection method, cleanability criteria, orientation and drainage expectations. A flush window geometry can support cleanability, but the complete installation includes the mating flange, seal, welds and surrounding vessel surface. Our sanitary versus industrial sight glass guide explains the additional checks.

Typical Applications

• Mixing, blending and batching vessels
• Reactors, receivers and process tanks
• Food, beverage, dairy and cosmetic equipment
• Pharmaceutical and biotechnology process equipment
• Chemical and water-treatment vessels, subject to material compatibility
• Equipment requiring a compact bolted circular observation window

Application names do not confirm suitability. The exact medium, pressure, vacuum, temperature, cleaning process, thermal cycle, flange interface and required documentation remain part of the selection.

Why Work with Borlan Fluid?

Borlan Fluid manufactures fused, flanged, union, pipeline and customized stainless-steel sight glass products. For a BL-SJFL-XX project, our team can review the equipment drawing, bolt pattern, clear viewing requirement, service conditions, seal, material and documentation before confirming the quotation and production drawing.

For application videos and factory updates, visit the Borlan Fluid YouTube channel and LinkedIn page. A product-specific video should be linked only after the filmed size and configuration have been verified.

Frequently Asked Questions

What does XX mean in BL-SJFL-XX?

XX is replaced by the selected nominal size. The catalog range shown on this page covers DN50 through DN200.

Does PN16 mean every BL-SJFL sight glass can operate at 16 bar?

No. PN16 is the catalog flange dimensional designation. Allowable working pressure must be confirmed for the exact size, fused assembly, temperature, seal, mating flange and applicable design requirements.

Why is a soft seal required?

The catalog instructs users to apply a soft seal at the contact face. The seal helps accommodate the interface without introducing hard point loading. Material and dimensions must match the medium, temperature and approved drawing.

How quickly can the temperature change?

The catalog instruction for the fused series is to keep heating and cooling within 2-3°C per minute. Provide the full process and cleaning cycle for confirmation.

Can the flange dimensions be customized?

Standard and non-standard requirements can be reviewed, but a customized bolt pattern or diameter requires a dimensioned drawing and a new technical confirmation rather than an assumption based on the catalog table.

What information is needed for a quotation?

Send the nominal size, mating-flange drawing, medium, normal and maximum pressure, vacuum, temperature range, heating and cooling rate, metal grade, seal requirement, surface finish, viewing requirement, quantity, destination country and required inspection documents.

Request a Quote

Send Borlan Fluid your DN size, mating-flange drawing, medium, pressure or vacuum, minimum and maximum temperature, heating and cooling rate, metal grade, seal requirement, surface finish, quantity, destination country and documentation requirements. We will review the BL-SJFL-XX configuration and prepare a quotation based on the confirmed supply scope.