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Installation Considerations and Common Types of Sight Glasses

Sight glasses, also known as sight gauges or flow indicators, are safety accessories used to observe the internal conditions of containers and equipment. They are widely employed in various industrial equipment and pipeline systems, enabling operators to visually monitor critical information such as material flow, liquid level changes, and color. Through sight glasses, personnel can quickly grasp equipment operating status, thereby ensuring the safety and stability of production processes. Therefore, regular inspection of sight glasses is particularly important.

I. Common Types of Sight Glasses:
Sight glasses come in numerous varieties, commonly categorized as follows:

1. By Shape: Round sight glasses and rectangular sight glasses.

2. By Purpose: Inspection sight glasses and illuminating sight glasses.

3. By Structure: Sight glasses with or without lining, with neck, with cover, double-layer safety, insulated, with wiper, with flushing device, and types specially designed for powdered materials.

The structure of a sight glass primarily consists of key components such as the body (flange/base), sight glass window, and valve assembly. Regarding materials, the body is typically made of carbon steel or stainless steel. The sight window glass may be made of soda-lime glass, tempered borosilicate glass, or quartz glass, each with specific applicable temperature ranges. For example:

• Soda-lime glass has a maximum temperature limit of 150°C and a thermal shock resistance range of 120°C to 20°C.

• Quartz glass has a much higher limit of 800°C and a thermal shock resistance range of 500°C to 20°C.

Furthermore, connection methods include threaded connections and flanged connections, chosen based on actual requirements. Sight glasses play a vital role across numerous industrial fields like petroleum, chemical, chemical fiber, pharmaceutical, and food processing. They are extensively used in various production facilities to facilitate observation of internal material conditions.

II. Sight Glass Installation and Usage Considerations:
When installing and using sight glasses, it is essential to adhere to a series of operational specifications. These standards not only affect the performance and lifespan of the sight glass but also directly impact the safety and efficiency of the production equipment. Below are key points for user reference:

1. Follow the Operation Manual: Always read and strictly follow the sight glass operation manual to ensure correct and safe installation and usage.

2. Regular Inspection and Maintenance: Conduct periodic comprehensive inspections of the sight glass, including checking the clarity of the window and the flexibility of valve components, to ensure it remains in good condition. Perform regular maintenance as needed to extend its service life.

3. Prevent Over-Pressure: Ensure the pressure exerted on the sight glass during installation and operation remains within the allowable range. Avoid excessive pressure that could cause damage or performance degradation.

4. Prevent Corrosion and Contamination: Protect the sight glass from corrosion and contamination to ensure it accurately and clearly displays the internal operating state of the equipment.

Adhering to these considerations will help ensure the safe and stable operation of the sight glass, thereby providing strong safeguards for the safety and efficiency of production equipment.

Specific Installation Instructions:

• Ensure the flanges and threads at the pipeline connection points are clean and undamaged. This task should be performed by qualified personnel.

• When installing the sight window, carefully confirm the sight glass body/seating surface is flat and smooth. Ensure the sealing gasket between the glass and the body is installed flat, undamaged, and free of grease adhesion.

• Before tightening screws, confirm the sight glass and cover are correctly positioned, then tighten the screws gradually and evenly.

• The operating pressure of the sight glass must be kept within the allowable range to ensure safe operation.

• For sight glasses with hinged or threaded connections, carefully inspect the sealing gasket installation before operation. Re-tighten bolts if necessary to ensure good sealing between the sight port and the sight glass aperture, and between the sight glass and the welded flange. Also, ensure the vessel pressure does not exceed the rated value.

• After installation, avoid applying any additional force or stress to the sight glass to prevent uneven loading and potential glass breakage.

Example Applications:

• Tubular Sight Glass (e.g., for Oil/Chemical Industries): Widely used in petroleum, chemical, and other industries to observe the flow and reaction of liquids, gases, steam, and other media. Standards include HG-S07-126 (Carbon Steel) and HG-S07-127 (Stainless Steel). Key specifications:

  • Max. Operating Pressure: 25 kgf/cm² (2.45 MPa)

  • Allowable Medium Temp.: 0 to 200°C

  • Window Material: Tempered Borosilicate Glass (Thermal Shock Resistance: 180°C)

  • Body Material Options: Carbon Steel, Stainless Steel, Lined, or FRP (Fiberglass Reinforced Plastic)

  • Window Material Options: Tempered Borosilicate Glass or Quartz Glass

  • Operating Temp. Range: -0°C to 250°C or 0°C to 800°C (depending on glass)

  • Nominal Pressure (PN): 0.6 ~ 2.5 MPa

  • Sealing Material: NBR Rubber or PTFE (Teflon)

  • Connection: Threaded or Flanged

  • Excellent thermal shock resistance (< 60°C change).

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• Innovative Oil Sight Glass (Easy-Clean Design): Features a body with an internal cavity housing an inlet pipe and an outlet pipe, both connected to the cavity. Transparent sight windows are installed on both sides for observation. A specially designed quick-cleaning mechanism includes:

  • A shaft slidably mounted relative to the transparent window.

  • A scraper blade detachably mounted on one end of the shaft inside the cavity.

  • A limit collar on the other end of the shaft.

  • A spring washer movably installed on the limit collar.

  • A compression spring located between the spring washer and the limit collar.

  • Rotating the shaft drives the scraper blade in a circular motion, easily removing condensate from the transparent window to maintain visibility.

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  • Key Design Advantages:

    • The compression spring and limit collar ensure the scraper blade tightly contacts the window for thorough cleaning without dead zones.

    • Sealing grooves and rings on the shaft enhance sealing and prevent leakage.

    • Clamping plates on the body sides have recesses matching the windows, simplifying installation and improving sealing via body grooves/rings.

    • Fixed sampling ports and thermometer ports allow connection of sampling tubes and high-precision thermometers for real-time oil monitoring.

    • The thermometer probe is located at the inlet pipe outlet.

    • The outlet pipe port inside the cavity is higher than the cavity's lowest point, ensuring measurement accuracy and safety.

    • An orifice plate is installed at the connection point of the sampling valve and tube to optimize sampling.

    • The sampling tube end has a threaded cap for easy disassembly and cleaning.

    • Inlet and outlet pipes have connection flanges.

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    • Overall Benefit: Enables convenient cleaning of the window inner walls without disassembly, allowing continuous observation and eliminating safety hazards caused by inability to monitor return oil flow.