BL-NAFL-XX NA Flange for Fused Sight Glass

NA Flange for Modular Fused Sight Glass Installation

El Borlan Fluid BL-NAFL-XX NA flange is a companion mounting flange designed for use with a matching Borlan fused sight glass. It provides the bolted outer support and stepped internal profile required to locate and secure the compatible observation window. Catalog sizes cover 1.5, 2, 2.5, 3, 3.5 and 4 inches. In the model code, XX represents the selected size.

This page describes the NA flange component itself. The matching raised fused window is identified separately as BL-NASJFL-XX. Buyers can order the required component or request a reviewed flange-and-window combination. The exact metal grade, mating sight glass, soft seal, fasteners, pressure, vacuum, temperature and documentation must be confirmed for the selected project.

What Is an NA Flange?

An NA flange is a compact companion flange used to mount a compatible observation window to a vessel or process connection. The BL-NAFL-XX profile includes several locating diameters and heights, identified in the catalog as L1–L5 and H1–H3. These dimensions control how the matching window seats inside the flange and how the bolted sections come together.

“NA” should be treated as the name of this connection family, not as proof that every part described as NA is automatically interchangeable. The outside diameter, internal steps, number of screws, window profile and sealing arrangement must all match. Send Borlan Fluid the existing component drawing or measured interface when replacing an installed flange.

BL-NAFL-XX and BL-NASJFL-XX: Know the Difference

The two model families form a coordinated interface, but they are not the same item. A request for “NA flange” should state whether the buyer needs the flange only, the fused window only, fasteners and seals, or a complete reviewed assembly. This distinction prevents missing components and reduces dimensional mismatch during installation.

Key Product Features

• Purpose-built companion component: designed to work with a corresponding Borlan fused sight glass rather than a generic flat window.
• Six catalog sizes: 1.5, 2, 2.5, 3, 3.5 and 4 inches.
• Defined stepped profile: L1–L5 and H1–H3 dimensions help identify the seating and support geometry.
• Bolted assembly: four screws are shown for 1.5–2.5 inches and eight screws for 3–4 inches.
• Modular replacement: the flange and fused observation window can be identified separately when a compatible replacement is required.
• Project review: material, seal, fasteners, finish and operating conditions can be reviewed against the buyer’s equipment and documentation requirements.

Catalog Reference Dimensions

The dimensions below are transcribed from the current Borlan catalog and are stated in millimetres. They are reference dimensions for product identification and quotation. Confirm the selected drawing before fabrication, welding, drilling or replacement work.

How the NA Flange Works with a Fused Sight Glass

The NA flange provides the external mechanical support, while the matching fused window provides the process observation surface. In the Borlan fused construction, the glass and metal window section are joined into one component. This can create a compact observation point with a flatter process-contact surface than a conventional multi-part retained-glass arrangement.

The NA connection does not eliminate the need for a correct seal or controlled assembly. The catalog instructs users of the fused sight glass series to use a soft seal at the contact face. The correct seal material and geometry depend on the medium, temperature, cleaning process and mating components. For a broader explanation of the available structures, see our industrial sight glass types guide.

Installation and Replacement Checks

Before installation, compare the complete dimension set rather than matching only the nominal inch size. Verify L1 through L5, H1 through H3, screw count, screw specification, locating shoulder, contact face and the corresponding fused window profile. Clean the mating surfaces and check that they are flat, aligned and free of damage.

Apply fastener load gradually and evenly using the approved assembly procedure. Do not force a mismatched part into the recess, use the bolts to correct alignment or allow connected equipment to place bending load on the observation window. When replacing one component in an existing assembly, inspect the flange, fused window, soft seal and fasteners as a system.

Pressure, Temperature and Thermal Cycling

The catalog describes enhanced pressure and temperature performance for the fused sight glass family and gives a series-level reference of at least 6 bar. This general description is not a universal allowable working pressure for every BL-NAFL size or completed assembly. Actual limits depend on the matching window, dimensions, material, temperature, seal, bolt loading, installation and applicable design rules.

The Borlan catalog also states that heating and cooling of fused sight glass products should not exceed 2–3°C per minute. Sudden hot-to-cold or cold-to-hot exposure can create thermal stress even when the steady operating temperature appears acceptable. Include startup, shutdown, cleaning, sterilization and abnormal temperature events in the review. Our sight glass thermal shock guide explains why temperature change rate must be specified separately from maximum temperature.

Material and Surface-Finish Options

The catalog page does not assign one metal grade to every BL-NAFL-XX size. Specify the required metal grade, surface finish, passivation, traceability and documentation when requesting a quotation. Do not assume that a flange photographed in one configuration defines the material supplied for every order.

If the assembly is intended for hygienic processing, provide the required contact material, roughness, cleaning chemicals, drainability expectation and documentation. A smooth fused window can support a cleaner interface, but the word “fused” alone does not establish compliance with a particular sanitary standard. The differences between application categories are discussed in our sanitary versus industrial sight glass guide.

Typical Selection Scenarios

• Building a compact vessel observation point around a matching Borlan fused window.
• Replacing an existing NA flange after confirming the original profile and screw arrangement.
• Ordering the flange and BL-NASJFL fused sight glass as a reviewed combination.
• Preparing a customized vessel connection where the equipment designer supplies the mating drawing and operating conditions.

Application names do not confirm suitability. Chemical processing, food, beverage, pharmaceutical, biotechnology and general vessel applications can impose very different requirements. Selection must follow the actual medium, pressure, vacuum, temperature, thermal cycle, cleaning method and required records.

Why Work with Borlan Fluid?

Borlan Fluid supplies sight glass components, fused observation windows, sight glass lights and related vessel accessories. For NA connection projects, our value is the ability to review the mounting flange and observation window together, identify the required supply scope and discuss dimensional or documentation needs before production.

Buyers comparing window structures can also read our fused versus conventional bolted sight glass guide. For application videos and factory updates, visit the Borlan Fluid YouTube channel and LinkedIn page. A product-specific video will be linked after its size and configuration are verified.

Preguntas frecuentes

Is BL-NAFL-XX supplied with the glass window?

BL-NAFL-XX identifies the NA flange component. State whether you need the flange only, the matching BL-NASJFL fused window, seals, fasteners or a complete reviewed combination.

What does XX mean in the model number?

XX represents the selected size. The current catalog lists 1.5, 2, 2.5, 3, 3.5 and 4-inch NA flanges.

Can I replace an existing NA flange by nominal size alone?

No. Compare the full L1–L5 and H1–H3 dimensions, screw count, window profile and sealing interface. Send a drawing or clear measurements for replacement projects.

What material is the standard flange?

The catalog page does not define one grade for every size. Provide the required metal grade, surface finish and documentation so the quotation reflects the correct configuration.

What is the pressure rating?

The fused series has a catalog-level reference of at least 6 bar, but the allowable pressure of a completed assembly must be confirmed for its size, window, material, seal, temperature and installation.

What information is required for a quotation?

Send the NA flange size, required supply scope, mating-window model or drawing, medium, normal and maximum pressure, vacuum, temperature range, heating and cooling rate, material, seal, surface finish, quantity, destination country and required inspection documents.

Request a Reviewed NA Flange Configuration

Send Borlan Fluid your size, mating-window drawing, required supply scope, medium, pressure or vacuum, minimum and maximum temperature, heating and cooling rate, material grade, seal requirement, surface finish, quantity, destination country and documentation requirements. We will review the BL-NAFL-XX interface and prepare a quotation for the confirmed configuration.