Visual oil inspection is: monitoring of the colour, sediment, clarity and water contamination levels of lubricants

The answer to visual oil inspection is simple....: “Stay ahead of future problems”.

To be a bit more precise. It’s not (only) taking an oil sample, sending it to the laboratory for chemical and physical tests. It’s even more simple. Many basic lubrication problems can be found by visual oil inspection.

Don’t underestimate the human eye!


Aren’t we all curious to know what’s going on with the oil inside of our equipment?

We can guess of course.

But taking away all guesswork, it’s just a matter of installing sight glasses. With this simple piece of glass you do have a continuous, visual monitoring of the colour, sediment, clarity and water contamination levels of your lubricants. Sight Glasses play an important role by allowing technicians to monitor the lube levels and condition. These devices provide a wealth of visual information.




standard-installed-sight-glassThe standard installed sight glasses on most pumps are often stained and discoloured over time, which makes inspecting the correct oil levels difficult.





3d-sight-glassA much more reliable option for ensuring proper oil levels is to use a 3D sight glass, permitting to view the oil level from any angle.






Investigations turn out that 60-70% of all lubrication-related problems are caused by contamination. With oil sight glasses the presence of contaminants, especially water, can easily be determined. Oil sight glasses allow users to isolate drain water and other contaminants from their oil. Water and sediment naturally sink to the bottom of the oil reservoir. Without any method to remove this, water will go unnoticed, and continue damaging your equipment and degrading the quality of your oil. 


Made from long-lasting, high strength acrylic, the oil side glass is available in a variety of sizes and styles. Their durable construction allows them to be installed in a range of environments, temperature and conditions. They are perfect for pumps, gearboxes, bearing houses and other lubrication critical pieces of equipment. Oil Sight Glasses will give operators the ability to catch small changes to the quality of the oil. Identifying small problems and taking corrective actions will prevent potential equipment failures.



Visual Oil Analysis Products

Health and Lube-Level Monitor


The Visual Oil Analysis Product Line

To facilitate various equipment configurations, the Visual Oil Analysis product line includes several models:


Vertical Sight Glass

oil-sight-glass-verticalPremium acrylic, monolithic oil sight glass designed to withstand the harshest environments. The sight glass is a single piece of acrylic and offered in 1-ounce or 3-ounce bottle sizes and with either ¼”, 3/8”, ½” or ¾” NPT.


The Oil Sight Glass is installed directly to a drain port located at the bottom of a reservoir or with an elbow for drain ports located on the side of the equipment. The spring loaded drain valve is utilized to drain off any water contamination.


Any sediment or particles in the lubricating fluid will matriculate to the Oil Sight Glass where, upon inspection, the user can determine the appropriate action.


Machined out of one solid piece of acrylic, this heavy-duty design eliminates any bonded parts that would wear out over time. With thicker walls and increased chemical compatibility, this robust Oil Sight Glass is used in the harshest environments.


These parts are designed to handle higher pressures as well as exposure to caustic chemicals that would potentially degrade O-rings or bonded parts in the other Oil Sight Glass designs. The Vertical Sight Glass is the perfect product for the most aggressive applications designs.



For detailed information on Vertical Sight Glasses please visit our Product page.



Large Volume Oil Sight Glass



Large Volume Sizes for Special Applications

Most Bottom Sediment and Water Bowls, BS&W, Bulls Eyes etc. fail to provide the necessary volume when high water volume water accumulation is a problem.


When reservoirs or equipment produce so much water such that other products cannot hold it all between maintenance checks, the Large Volume Oil Sight Glass provides the extra storage to keep water out of the oil until it can be drained.







application-large-volume-oil-sight-glassCommonly used on large oil reservoirs, or on equipment operated in environments with regular high pressure wash downs or high condensation problems, where water contamination cannot be avoided or minimized.


The added volumes of this line of products provide continuous fluid monitoring of the clarity, colour, sediment and water contamination. 


Operators have the ability to see your oil, monitor it and drain the water accumulation as soon as it appears for equipment. And having the added advantage of storing more water accumulations between service or monitoring intervals.


The Esco Large Volume Oil Sight Glass vertical models of 16 oz and 32 oz capacity are used in situations where water contamination is severe or the operators want to observe larger volumes of oil.


For detailed information on VerticalLarge Volume Oil Sight Glasses please visit our Product page.




High Temperature Oil Sight Glass

High Temperature Style when the Operation is Hot

The High Temperature Oil Sight Glass is your answer when radiant heat from nearby equipment or unusually high operating temperatures exceed the safe use of the Legacy Oil Sight Glasses. Only available in Vertical Style, the Pyrex Glass and Teflon End Caps allow for operating and environmental temperatures up to 450° Fahrenheit (232° Celcius). So even under extreme temperature conditions, you will still be able to visually monitor the oil qualities and expel water contamination.


This enhanced product continues to provide the visual oil management benefits when the Tattle Tale, Bottom Sediment and Water Bowl, BS&W, Pig Tail or Bulls Eye fail to operate due to high temperatures. High Temperature Oil Sight Glass offered in 1 ounce and 3 ounce bottle sizes in either 1/4”, 3/8”, or 1/2” NPT.  


 For detailed information on High Temperature Oil Sight Glasses please visit our Product page.


3-D Bullseye Oil Sight Glass

3-D BullsEye - A Better Alternative to Sight Windows on Oil Reservoirs

3d-bullseyeEsco has developed a product to make the job of a lubrication technician or maintenance manager easier when checking both colour and clarity of the oil on small wet sump applications, such as pumps and gearboxes, while allowing an unobstructed 360°view of the oil level from any angle.


The standard sight windows on oil reservoirs make it difficult to view the oil level, stain easily, and must be replaced often. Esco has improved upon the old-fashioned sight plug with the creation of a replacement sight window called the 3-D BullsEye.


The 3-D BullsEye is machined from one solid piece of impact resistant, high strength, stain-resistant cast acrylic. It has excellent resistance to hydrocarbon and petroleum-based products, hydraulic fluids, most silicone fluids, and fuels. A detailed chemical resistance chart can be downloaded here.


3-D BullsEye sight window offered in 1/4”, 3/8”, 1/2”, 3/4”, 1” , 1 1/4”, 1 1/2”, and 2” NPT sizes and M10X1.0, M10X1.5, M12X1.5 M16X1.5, M20X1.5, M22X1.5 M24X1.5, M26X1.5, M27X1.5, M30X1.5, M30X2.0, and M33X1.5 metric sizes.


The 3-D BullsEye is the perfect solution for quick oil level inspection.


Easily see your oil level with the 360◦ crystal clear view that the 3-D BullsEye offers.


For detailed information on 3D-BullsEye please visit our Product page.




Oil Level Indicator

oil-level-indicator-escoThe Oil Level Indicator (OLI) was developed in response to the need of maintenance professionals to gauge the oil level inside large tanks, gearboxes and reservoirs.


When water contamination is not a problem or when a regular Esco Oil Sight Glass is already installed at the drain port, the Oil Level Indicator can be utilized to monitor oil level.


The oil gauge indicator is a clear acrylic tube with ½” NPT threads at each end. Red and green decals are included with the OLI to mark upper and lower limits, or to designate running oil level and idle oil level.


Oil Gauge Indicators can be installed with the optional breather* at the top ½” NPT port as seen on the Esco Oil Sight Glass and Level Monitor. If the user requires a closed loop, the ½” NPT can be used as a connector port to feed back into the system.


Operators can visually monitor the oil for dirt and debris and take appropriate preventive action.


"Why use an old style vented oil gauge that is difficult to see through and has breakable glass,

when you can install a crystal clear, strong acrylic Esco Oil Level Indicator that offers 360° of oil viewing?"


The Oil Level Indicator is offered in 3”, 6”, 9”, 12” and 15” lengths. Longer lengths, custom options, and additional hardware available. The Oil Level Indicator (OLI) is a tube of cast acrylic offered in various lengths which allows you to easily see a 360° view of your oil level in equipment. Made to replace the brass and glass sight gauges that stain and leak, the OLI is built to last.


For detailed information on Oil Level Indicator please visit our Product page.




Oil Sight Glass & Level Monitor

When properly installed at the oil reservoir drain port, the Oil Sight Glass & Level Monitor allows the user to view the oil colour, clarity, and accumulation of water or other contaminates.


  • The strong, clear cast acrylic body allows for viewing of the level.
  • The spring loaded drain valve is positioned to quickly discharge any water before
         it damages the oil lubricity.
  • Red and green Buna O-rings are included with the OSGL to mark upper and lower
         limits, or to designate running oil level and idle oil level.
  • Each Oil Sight Gauge & Level Monitor comes with a 2 micron breather, which
         allows the oil level to equalize with the level inside the system.


If you require a closed loop system, install the OSGL without the breather and use the top opening to port back into your equipment.


oil-sight-glass-dual-portThe height of the upper column comes in heights from 3" to 24" to correspond to the distance from the oil reservoir access port and the maximum height the oil will reach. Custom sizes are available.


A Dual Port Oil Sight Glass & Level Monitor version is available with a second 3/8" NPT port opposite the installation nipple to allow the installation of a Sample Port for oil sampling. Oil Sight Glass & Level Monitor offered with 3/8” NPT single or dual side ports and in 3”, 6”, 9”, 12”, 15”, 18”, or 24” lengths.


The Esco Oil Sight Glass and Level Monitor (OSGL) provide continuous and instantaneous monitoring of oil clarity, water contamination and oil level. This all-in-one tool allows for a quick and easy inspection for predictive maintenance professionals to easily assess what is going on in their equipment.


For detailed information on Oil Sight Glass & Level Monitor please visit our Product page.








Standard Installation of OSG (Bottom Sediment and Water Bowl)

standard-installation-of-oil-sight-glass-bottom-sediment-and-water-bowlOil Sight Glasses should be installed at the lowest point possible. Typically these are installed on a drain port using a 90° piping elbow.


The Oil Sight Glass sits below the oil reservoir, so all water and sediment sinks to the bottom of the reservoir and collects in the Oil Sight Glass. This removes the harmful free flowing water which the user can then drain when necessary.


If there is not adequate vertical space for installation then Esco’s Horizontal Oil Sight Glass is recommended (See instructions on Horizontal installation).





Standard Installation of Horizontal Oil Sight Glass

standard-installation-of-horizontal-oil-sight-glasshorizontal-oil-sight-glassEsco developed the Horizontal Oil Sight Glass for installations that did not have enough vertical space for our standard Oil Sight Glass.


The Horizontal Oil Sight Glass installs directly into the drain port and still allows for the collecting and draining of water and sediment.





Standard Installation of Oil Level Indicator (Vented)


Oil Level Indicator shows an accurate level of oil inside the reservoir.


Breather cap on top allows for equalization of pressure without pulling in contaminants.


Red and Green O-rings or stickers mark the upper and lower limit of the oil level (as determined by user).







Standard Installation of Oil Level Indicator (Closed Loop)

standard-installation-of-oil-level-indicator-closed-loopoil-level-indicator-closed-loopOil Level Indicator shows an accurate level of oil inside the reservoir.

Pipe out of the top and then back into your oil reservoir to make a closed loop system.

Red and Green O-Rings or stickers show the upper and lower level limits (as determined by the user).








Oil Level Indicator in use with Horizontal Oil Sight Glass
(when vertical space is limited)

oil-level-indicator-in-use-with-horizontal-oil-sight-glassoil-level-indicator-horizontal-oil-sight-glassThe Oil Level Indicator shows the level of oil inside of the reservoir.

A breather is installed on top allows the device to vent without pulling in outside contaminants.

Horizontal Oil Sight Glass is installed at the lowest point.

This way any water or sediment will be collected and drained as needed. Horizontal style Oil Sight Glass requires less vertical space for installation.







Standard Installation of OSG & Level Monitor (Closed Loop)

standard-installation-of-oil-sight-glass-and-level-monitor-closed-looposg-level-monitor-closed-loopOil Sight Glass & Level Monitor shows an accurate level of oil inside the reservoir.

Pipe out of the top and then back into your oil reservoir to make a closed loop system.

Red and Green O-Rings or stickers show the upper and lower level limits (as determined by the user). 








Standard Installation of Oil Sight Glass & Level Monitor (Vented)

standard-installation-of-oil-sight-glass-and-level-monitor-ventedosg-level-monitor-ventedOil Sight Glass & Level Monitor shows an accurate level of oil inside the reservoir.

Breather on top allows for pressure to equalize without pulling in contaminants.

Red and Green O-Rings or stickers show the upper and lower level limits (as determined by the user).









Sampling Through Dual Port Oil Sight Glass & Level Monitor

sampling -through-dual-port-oil-sight-glass-and-level-monitor
















Dual Port Oil Sight Glass & Level Monitor can be used to sample oil.


The user can install a pitot tube (which has been cut to desired length and bent to desired level).

Use a vacuum pump with a special fitting on the hose to draw sample from the pitot tube.

The oil sample is collected in plastic container for later analysis.



Proper Level Monitor Installation

When installing the Esco Oil Sight Glass and Level Monitor, proper vertical alignment cannot be attained by threading the nipple directly into the drain valve.

Installers compensate by over-tightening the connection to move the OSGL into the correct upright position.

This over-tightening can lead to cracks in the acrylic and compromise the effectiveness of the OSGL.


Esco suggests using a Union when installing the OSGL.



Problem solved!


Proper vertical alignment is easily attained with the use of a union and there is no longer a threat of over-tightening the Connection and cracking the Level Monitor. 



To help Esco’s customers to mount their levelers correctly, the installation guidelines on the label of every OSGL has been updated to include the use of a union.

Responding to customer needs to view the levels in larger oil reservoirs Esco began to manufacture 15”, 18” and 24” Oil Sight Glass Level Monitors.

Esco recommends that on Level Monitors longer than 12” a support bracket should be utilized for stability




Download the brochure "How to install Oil Sight Glasses"





or watch the "Esco's Oil Sight Glasses Installation" and/or "Esco 3D-BullsEye installation" video below: