Editorial Technical Reference

Level Gauge / Sight Glass

This page explains how Level Gauge / Sight Glass is classified within Chemical Manufacturing. Technical values and manufacturer relationships are research references; confirm the current specification and supplier evidence for each order.

Technical Definition & Core Assembly

A transparent window or gauge used to visually monitor the liquid level inside a vessel or separator.

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Product Specifications

Technical details and manufacturing context for Level Gauge / Sight Glass

Definition
The Level Gauge / Sight Glass is a component used in chemical manufacturing, specifically as a part of a Vapor-Liquid Separator. It provides a direct visual indication of the interface level between the liquid and vapor phases within the vessel. This allows operators to monitor separation efficiency, control liquid drainage, and ensure safe operating levels. The gauge is mounted on the side of the separator vessel, with a transparent material—typically tempered borosilicate glass or polycarbonate—that allows light to pass through, making the liquid level visible from the outside. In gauges with markings, the level is read against a calibrated scale. The housing is typically made of stainless steel (304 or 316L), with 316L recommended for corrosive media. The glass material is borosilicate 3.3, which offers high thermal shock resistance. Sealing materials include PTFE or EPDM, with PTFE providing chemical resistance. The nominal diameter ranges from DN15 to DN100, with standard sizes for piping connections per ISO 7005. Operating pressure is 1.0–1.6 MPa. Operating temperature ranges from -40°C to 200°C, with a note that above 200°C requires borosilicate glass. Connection types are flanged or threaded, with flanged recommended for high pressure, per ISO 7005. Visibility length ranges from 200 to 2000 mm, with custom lengths available. Weight ranges from 2 to 15 kg, depending on size and material. These values are directory reference ranges and must be confirmed for the actual model and application with the legal manufacturer or supplier. The product is a neutral directory listing, not a manufacturer or seller. Always verify model-specific values and standards with the supplier.
Working Principle
The sight glass or gauge is mounted on the side of the separator vessel. The transparent material (typically glass or a polymer) allows light to pass through, making the liquid level inside the vessel visible from the outside. In gauges with markings, the level is read against a calibrated scale. The operator observes the interface between liquid and vapor phases to assess separation efficiency and control liquid drainage. The gauge operates based on the principle of visual transparency, with no moving parts, and requires a clear line of sight. The material selection, such as borosilicate glass for high temperatures or polycarbonate for impact resistance, affects the operating range. The housing and sealing materials must be compatible with the process media to prevent leakage and ensure safe operation.
Common Materials
Tempered Borosilicate Glass, Polycarbonate, Stainless Steel (housing)
Technical Parameters
ParameterTypical rangeNotes & selection driver
Nominal DiameterDN15–DN100 mmStandard sizes for piping connectionsISO 7005
Operating Pressure1.0–1.6 MPa
Operating Temperature-40–200 °CAbove 200°C requires borosilicate glass
Body Material304/316L316L for corrosive mediaASTM A240
Glass Materialborosilicate 3.3High thermal shock resistanceISO 3585
Sealing MaterialPTFE/EPDMPTFE for chemical resistance
Connection Typeflanged/threadedFlanged for high pressureISO 7005
Visibility Length200–2000 mmCustom lengths available
Weight2–15 kgDepends on size and material

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM
  • Transparent Tube / Window Part
    Provides the visual medium to see the liquid level.
    Material: Tempered Borosilicate Glass or Polycarbonate
  • Gasket / Seal Part
    Creates a pressure-tight seal between the glass and the metal housing.
    Material: PTFE, Viton, or EPDM
  • End Fitting / Housing Part
    Metal assembly that connects the sight glass to the vessel and protects the glass.
    Material: Stainless Steel (304/316)
  • Protective Guard (optional) Optional Part
    A metal cage or shield to protect the glass from physical impact.
    Material: Stainless Steel

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Vapor-Liquid Separator
View system integration details

Industrial Ecosystem & Supply Chain Structure

Complementary Systems
Downstream Applications
Specialized Tooling

Application Fit & Sizing Matrix

Operational Limits
pressure: Up to 25 bar (standard), up to 100 bar with reinforced designs
other spec: Flow velocity < 2 m/s to prevent erosion, slurry concentration < 30% solids by weight for clear visibility
temperature: -20°C to 200°C (standard borosilicate glass), up to 400°C with quartz glass
Media Compatibility
✓ Water and aqueous solutions ✓ Hydrocarbon liquids (oil, fuels) ✓ Chemical process fluids (acids, bases at moderate concentrations)
Unsuitable: Hydrofluoric acid or high-concentration caustic solutions (rapid glass corrosion)
Sizing Data Required
  • Vessel/pipe diameter and connection type (flange size, thread specification)
  • Required visible level range (minimum to maximum measurement height)
  • Process fluid properties (density, viscosity, corrosiveness)

Reliability & Engineering Risk Analysis

Failure Mode & Root Cause
Glass Cracking or Shattering
Cause: Thermal shock from rapid temperature changes, mechanical stress from improper installation or external impacts, or pressure surges exceeding design limits.
Leakage at Seals or Gaskets
Cause: Deterioration of sealing materials due to chemical attack from process fluids, aging/embrittlement from temperature cycling, or improper torque during assembly leading to compression loss.
Maintenance Indicators
  • Visible cracks, chips, or clouding/opacity in the glass that obscures level indication
  • Fluid weeping or dripping around the glass seals, gaskets, or body connections
Engineering Tips
  • Install protective shields or guards to prevent mechanical damage and consider using armored or double-pane glass designs for high-pressure/temperature services
  • Implement a routine inspection schedule for seal integrity and use compatible gasket materials (e.g., PTFE, Grafoil) resistant to the specific process fluid's chemical and thermal properties

Indicative industry ranges for design and RFQ preparation. Confirm the exact figures and applicable standard with the manufacturer before specifying.

Compliance & Manufacturing Standards

Applicable Standards
ISO 24450:2020 (Level gauges and sight glasses) ASME B40.100 (Pressure Gauges and Gauge Attachments) DIN 7080 (Sight glasses for pressure vessels)

Quoted from the published standard.

Manufacturing Precision
  • Bore diameter: +/-0.05mm
  • Parallelism of sealing surfaces: 0.02mm
Quality Inspection
  • Hydrostatic pressure test (1.5x rated pressure)
  • Visual inspection for clarity and defect-free glass

Manufacturers of Level Gauge / Sight Glass

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Frequently Asked Questions

What is the purpose of a level gauge in a separator?

It provides a direct visual indication of the liquid-vapor interface level, allowing operators to monitor separation efficiency and control liquid drainage to maintain safe operating levels.

What materials are commonly used for the sight glass?

Tempered borosilicate glass and polycarbonate are typical transparent materials. Borosilicate 3.3 is specified for high thermal shock resistance, and polycarbonate may be used for impact resistance. The housing is often stainless steel (304 or 316L).

What are the standard connection sizes and pressure ratings?

Nominal diameters range from DN15 to DN100 per ISO 7005. Operating pressure is 1.0–1.6 MPa. Always verify with the supplier for the specific model.

How should I verify the suitability of a level gauge for my application?

Check the operating temperature, pressure, and chemical compatibility of the wetted materials (glass, housing, seals) with your process media. Confirm the connection type and visibility length. Always consult the legal manufacturer or supplier for model-specific data and standards compliance.
Data basis: editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification
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