Stainless Steel Union Sight Glass | DIN and SMS

The Borlan Fluid stainless steel union sight glass provides a compact circular observation point for tanks, mixers, reactors and other process vessels. The standard product range supports DIN sizes from DN25 to DN200 and SMS sizes from 1 inch to 6 inches, with SS304 and SS316L material options. A wiper can be discussed where condensation, foam or product deposits may reduce visibility.

A union sight glass is selected as a complete pressure-boundary assembly rather than by nominal size alone. Before quotation, Borlan Fluid reviews the interface dimensions, visible opening, body and wetted material, glass, gasket, pressure or vacuum, operating and cleaning temperature, surface finish and optional accessories. Final suitability is confirmed against the approved drawing and actual service conditions.

What Is a Union Sight Glass?

A union sight glass uses a threaded retaining or union-style structure to hold the transparent window and seal against a welded or matching vessel connection. It creates a direct viewing port while keeping the external assembly relatively compact. Depending on the confirmed construction, the retaining component can be removed for glass, gasket or wiper service after the vessel has been isolated, depressurized, drained and made safe.

The term “union” describes the retaining and connection arrangement; it does not define one universal interchangeable standard. Two products carrying the same DN or inch designation can differ in outside diameter, overall height, clear aperture, thread form, welding interface and seal geometry. Compare the complete dimensions or send the existing drawing or sample before ordering a replacement. Our industrial sight glass types guide explains how union, flanged, tubular, strip and fused designs differ.

Key Features

• Compact vessel observation point: a circular window supports direct inspection of product level, color, foam, mixing or general vessel condition.
• DIN and SMS dimensional ranges: choose the interface that matches the equipment drawing rather than converting by nominal size alone.
• SS304 or SS316L options: body and product-contact material can be reviewed according to the medium and cleaning process.
• Serviceable union structure: the retaining arrangement supports controlled inspection and replacement of the window and seal.
• Optional wiper: available for discussion where deposits or condensation obstruct the viewing surface.
• Configuration review: glass, gasket, surface finish, connection details and documentation are confirmed for the specific project.
• Standard and customized supply: Borlan Fluid can review catalog sizes, replacement samples and non-standard drawings.

Technical Specifications

DIN Reference Dimensions

SMS Reference Dimensions

All dimensions are catalog reference values in millimeters. Confirm the approved drawing before machining, welding or ordering a replacement. Changes in material, glass, seal, wiper or custom interface may affect the final construction.

DIN or SMS: Which Interface Should You Choose?

Use the standard already defined by the tank or equipment drawing. DIN sizes are identified by DN designations, while the SMS table uses inch designations and corresponding tube outside diameters. A similar-looking nominal size does not prove that the union thread, outside diameter or mating seat will fit.

For replacement projects, provide the existing product’s overall height, body diameter, connection diameter, retaining-ring dimensions and clear opening. Photographs should include a scale, but a dimensioned drawing or physical sample gives stronger confirmation. Our clamp, union or flange selection guide helps buyers compare connection methods before changing the vessel design.

Material, Glass and Seal Selection

SS304 is widely used for general stainless-steel processing equipment, while SS316L may be preferred where the medium, cleaning chemicals or corrosion risk require a higher alloy grade. Material selection still depends on concentration, exposure time, temperature, cleaning procedure and the documentation required by the project. See our SS304 versus SS316L sight glass guide for the questions to review.

The metal grade alone does not determine the complete operating limit. Glass type, thickness, edge support, gasket material, surface condition, assembly geometry, pressure, vacuum and thermal cycling work together. A high maximum temperature for one component does not prove that the assembled sight glass can withstand rapid heating or cooling. Borlan Fluid confirms these items for the selected configuration rather than publishing one universal rating for every size.

Optional Wiper for Difficult Viewing Conditions

A manual wiper can help clear condensation, foam or soft deposits from the inner viewing surface. It may improve visibility without opening the vessel, but it is not appropriate for every medium or cleaning regime. Abrasive solids, crystallized deposits, aggressive chemicals or a poorly matched wiper material can damage the glass, seal or product-contact surface.

When requesting a wiper, describe the deposit, operating pressure, temperature, cleaning method, required wetted material and available handle clearance. The quotation and approved drawing should identify the handle, internal blade, shaft seal and related parts included in the supply.

Typical Applications

• Mixing, blending and batching tanks
• Reactors, receivers and process vessels
• Food, beverage and dairy equipment
• Pharmaceutical, biotechnology and cosmetic systems
• Water treatment and general process equipment
• Observation of liquid level, color, foam, mixing and product condition

No product name alone guarantees hygienic suitability. If the project requires CIP, SIP, a specified surface finish, drainability, material traceability or a particular inspection standard, include those requirements in the inquiry. The sanitary versus industrial sight glass guide lists the additional points that should be confirmed.

Installation and Maintenance Notes

• Confirm the mating dimensions and approved drawing before welding the vessel connection.
• Protect the glass and seal from welding heat, spatter, mechanical impact and contamination.
• Use the specified gasket and assemble the retaining components evenly.
• Do not use the sight glass as a step, lifting point or support for pipework.
• Inspect for chips, cracks, seal damage, corrosion, leakage or looseness before operation.
• Isolate, depressurize, drain, cool and make the vessel safe before disassembly or maintenance.

Why Work with Borlan Fluid?

Borlan Fluid manufactures stainless-steel sight glasses, sight glass lights and tank accessories for standard and customized equipment. For a union sight glass project, our team can review the drawing, DIN or SMS interface, material, clear viewing requirement, seal, wiper and supply scope before quotation. This helps reduce fit-up problems and repeated clarification during purchasing.

For application videos and factory updates, visit the Borlan Fluid YouTube channel and LinkedIn page. Product-specific video links can be added to this page after the matching configuration has been filmed and verified.

Frequently Asked Questions

Is a DIN union sight glass interchangeable with an SMS union sight glass?

Do not assume interchangeability. Compare the full interface, union thread, outside diameter, height, seal seat and visible opening against the equipment drawing.

What sizes are available?

The catalog range covers DIN DN25–DN200 and SMS 1–6 inches. Non-standard requirements can be reviewed from a dimensioned drawing.

Can I order SS316L wetted parts?

SS304 and SS316L are listed material options. State separately which body and product-contact parts must be SS316L and what material documentation is required.

Can the union sight glass include a wiper?

Yes, a manual wiper can be discussed. Suitability and supply scope depend on size, deposits, pressure, temperature, seal compatibility and available operating space.

What pressure and temperature can it handle?

There is no single verified rating for every size and configuration. Provide the normal and maximum pressure or vacuum, operating temperature, cleaning temperature and heating or cooling rate for technical confirmation.

What information is needed for a quotation?

Send the required DIN or SMS size, complete interface dimensions, medium, pressure or vacuum, temperature, metal grade, glass and seal requirements, surface finish, wiper need, quantity, destination country and any drawing or replacement sample information.

Request a Quote

Send Borlan Fluid your interface standard and size, equipment drawing, medium, pressure or vacuum, operating and cleaning temperature, body and wetted material, glass, seal, surface finish, wiper requirement, quantity and destination country. We will review the configuration and return a quotation based on the confirmed supply scope.