Oil sight glasses reveal lubricant condition

Lubrication Engineers is an authorized distributor of high-quality, affordable Xtract® sight glasses. These easy-to-install sight glasses take the guesswork out of fluid lubrication management. The Xtract sight glass product line enables continuous visual monitoring of the clarity, color, sediment and water contamination levels of your lubricants. Some models even allow you to easily remove the water by draining it right out of the system. The variety of sight glass solutions available will help advance your lubrication reliability program to the next level.


Xtract® Sight Glasses at a Glance

Xtract Sight Glasses


Xtract Oil Sight Glass

Xtract Oil Sight Glass

Xtract® Oil Sight Glass is suitable for most applications. Installed vertically or horizontally, it enables an immediate visual inspection of the oil. More importantly, this sight glass allows for the draining of any accumulated water, using the spring-loaded drain valve. The OSG can be installed directly to a drain port located at the bottom of a reservoir or with an elbow for drain ports located at the side of the equipment. The Xtract OSG is constructed of brass hardware (stainless steel optional) and a high performance polyamide bottle, capable of withstanding the pressure and temperature of most operating environments.

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Xtract Large Volume Oil Sight Glass

Xtract Large Volume OSG

Perfect when high water volume accumulation is a problem, the Xtract® Large Volume Oil Sight Glass provides the extra storage necessary to hold a large amount of water until it can be drained between maintenance checks. It is used on equipment that requires regular high-pressure washdowns or has high condensation problems, where water contamination cannot be avoided or minimized.

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Xtract Oil Sight Glass & Level Monitor

Xtract Oil Sight Glass and Level Monitor (OSGL)

The columnar style Xtract® Oil Sight Glass & Level Monitor is the all-in-one solution, allowing operators to manage oil levels, visually inspect lubricant condition, and easily drain off any water. Red and green decals are included with the OSGL to mark upper and lower limits, or to designate running oil level and idle oil level. This clear acrylic vertical oil sight glass provides a highly visible 360-degree view of the oil and can be hooked up to a desiccant breather, making it a substantial upgrade from an old vented brass-and-glass sight gauge.

The dual port model has a second 3/8″ NPT thread at 180 to allow the installation of a drain valve or access to the oil reservoir utilizing a pitot tube and a pitot sample adaptor.
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Xtract 3-D BullsEye Sight Glass

Xtract 3D Bullseye

Used in conjunction with a standard OSG or alone on equipment where there is no water problem, the Xtract® 3-D BullsEye™ Sight Glass window is another Xtract tool that provides easy visual monitoring of oil.

Unless you are standing directly in front of them, old-fashioned sight plugs on oil reservoirs make it difficult to view the oil level. The glass stains easily and is partially obscured by the hardware around it. LE’s solution is the 3-D BullsEye Sight Glass. This one-piece cylinder, made of a high-performance transparent polyamide, allows immediate and accurate visual oil level monitoring from virtually any angle. Engineered to outperform and outlast traditional view ports, the inherently strong material provides excellent impact, chemical and UV resistance.

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Xtract Oil Level Indicator

Xtract Oil Level Indicator

LE’s columnar style Xtract® Oil Level Indicator is recommended for monitoring the oil level inside large tanks, gearboxes or reservoirs when water contamination is not a problem. An old-style vented oil gauge made of brass and breakable glass can be replaced with an OLI (right), which is constructed of strong clear acrylic and provides a 360-degree view of the lubricant. In addition, you can attach a desiccant breather to the oil level indicator, an option not possible with the old style gauge.

The Xtract Oil Level Indicator can be used alone when there is no water problem or installed on equipment that also has a standard OSG. The sight glass allows the operator to visually inspect the condition of the oil and to take appropriate preventive action such as draining the water. The OLI is needed because the sight glass is situated too low to properly indicate oil level in this scenario.

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LE offers full-service support for all Xtract sight glasses and other reliability solutions

In addition to onsite equipment assessment, consultation and service, LE provides the following customization and value-added options:

  • Product recommendation, sizing and installation of oil sight glasses
  • Lubrication reliability training & education
  • Oil analysis program

LE is happy to offer industrial lubricant and reliability recommendations for a variety of industries and applications, and to provide product-specific data on all of our items to help you make the right decision. To learn more about our enhanced lubricants and lubricant reliability products, please contact LE today.


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Sight Glass Materials and Construction

Selecting the right tubing for a sight glass depends on the operating environment and the type of flanged connection required. Industrial sight glasses are manufactured from durable flange fittings and metal housings designed to resist corrosion and withstand demanding process conditions.

Flanged and Threaded Connection Types

Flanged sight glass connections with gaskets provide a secure, leak-proof seal for high-demand applications, while threaded NPT connections suit lighter-duty installations. A proper gasket or o-ring between the flange and the mounting surface prevents leaks and ensures long-term reliability. Operators should verify the pressure gage reading before and after installation to confirm seal integrity.

Gasket and O-Ring Sealing Options

Every sight glass requires a reliable seal, and the choice between a gasket and an o-ring depends on temperature, pressure, and chemical exposure. Seals made from viton offer excellent corrosion resistant performance against corrosive chemicals and aggressive fluids, while standard elastomer seals handle most general-purpose lubrication systems.

Corrosion Resistance and Chemical Compatibility

Sight glasses used in environments with corrosive chemicals must be constructed from corrosion resistant materials such as stainless steel or specialized polymer compounds. Exposure to steam and harsh process fluids can degrade standard brass hardware, making material selection critical for long service life. Mica shields provide an additional protective layer in high-temperature applications.

High Pressure and Steam Applications

In high pressure system and steam boilers environments, sight glasses must meet strict safety standards set by organizations like ANSI. Reinforced metal sight glass designs with a tempered borosilicate lens and teflon tape sealed connections ensure safe visual monitoring even under extreme operating conditions.

Explosion Proof and Intrinsically Safe Designs

Facilities handling volatile substances require explosion proof rated equipment. Luminaire illuminated sight glasses with light sources rated for hazardous areas allow operators to safely observe liquid levels and flow conditions without risk of ignition. Proper lighting ensures clear observation of process fluids at all times.

Sight Glass Accessories and Monitoring Features

Lighting and Illumination Options

Proper lighting enhances visibility through a sight glass, especially in dark enclosures or deep tank installations. LED luminaire assemblies mount directly to the sight glass body and provide bright, energy-efficient light for clear observation of fluid condition. Look for bubble indicators that confirm active flow within the system.

Condition Monitoring and Level Observation

Modern sight glasses support proactive condition monitoring programs by enabling continuous visual observation of lubricant clarity, color, and contamination. Operators can detect water accumulation, sediment buildup, and oil degradation before these issues cause equipment failure. Pairing a sight glass with a pressure gage provides a comprehensive view of system health.

Sight Glass Installation Best Practices

Tubing and Plumbing Connections

When routing tubing to a sight glass, ensure all fittings are properly sealed with teflon tape or appropriate thread sealant. Use compatible aluminum or stainless steel hardware and hex nut fasteners to secure the assembly and prevent vibration-induced loosening. Verify that all flange connections include the correct gaskets for the operating pressure range.

Column and Reflex Style Mounting

Column style sight glasses mount vertically between two isolation valves, while reflex gauge designs use prism effects to clearly distinguish between liquid and gas phases. Both styles offer reliable level indication for tank and reservoir applications. A polymer or metal housing protects the lens from impact and corrosion in harsh industrial settings.