When a company decides to instigate on-site oil analysis, obvious questions such as: “What tools and equipment are we going to use?” and “What types of tests do we want to perform on-site?” are typically asked. These questions are quickly answered with another question: “What kind of budget do we have for this project?”
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While with unlimited funds, the decision would be far simpler; the reality for most, if not all individuals just beginning an oil analysis program, is that the budget is most likely undersized. With an undersized budget and oversized ambitions for an on-site oil analysis program, deciding which tools to procure and in what order to do so can be critical to the on-site oil analysis program’s success.
Categories of Oil Analysis Testing
When spending budgeted money on an oil analysis program, choosing which tests should be performed on-site and which test slates are best deployed by the off-site lab is the most important decision. Typical test slates can be divided into three categories: on-site screening, routine laboratory analysis and exception testing.
On-site screening tests can be performed at various frequencies, depending on machine, lubricant stressing conditions and the reliability objectives of the asset owner. Machines and lubricants that operate at high loads/speed and/or are exposed to high temperatures and environmental contaminants need more frequent screening.
The type of screening test needed is machine- and application- dependent. For instance, oil exposed to steam would need to be screened for water. High temperature lubricants, however, don’t need water assessments but rather tests that indicate thermal distress, such as viscosity or blotter spot tests.
Routine tests are also application- and machine-dependent. They are either performed on-site by a fully equipped laboratory, or by an off-site commercial laboratory. Common routine tests include particle counting, elemental spectroscopy, viscosity, infrared spectroscopy, acid number and moisture analysis, among many other possibilities.
Just as the name implies, exception tests are triggered by a nonconforming inspection or test result coming from a screening test or a routine test. Tests that are performed on exception in some applications are performed routinely in others.
Basically, the idea behind exception testing is to perform expensive and sometimes manually intensive tests only when needed. Exception tests enable the oil analysis practitioner to explore more deeply into the oil’s database.
Analytical ferrography, demulsibility, XRF and scanning electron microscopy are examples of exception tests. An exception test might also be a test that was not included on a routine test slate for streamlining or budgetary reasons.
On-site Oil Analysis Strategy
With rare exception, the goal of on-site oil analysis is not to replace the commercial lab. Commercial labs can invest millions of dollars in state-of-the-art scientific instruments. A reputable commercial lab gives the on-site lab the flexibility to have numerous exception and lubricant property tests performed when needed without having to carry the associated costs of hardware and training.
Except when a large number of samples need to be routinely analyzed, it is unrealistic for an on-site lab to be sufficiently equipped with the range of analysis instruments typically needed.
Consider the following key points when selecting on-site tests:
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Frequency or total number of tests administered each month. Is it realistic to expect 500 particle counts to be performed each month?
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Most critical and most time-sensitive data. Are there critical assets where there is little or no time between a potential failure starting and a functional failure occurring?
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Least skill intensive. Is it realistic to expect a lube technician or mechanic to become proficient at running complex scientific equipment?
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Within budget. Is it realistic to expect to get all the data needed with the budgeted amount?
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Off-site versus on-site costs. Is it cost beneficial to prescreen samples to reduce the number of samples sent off-site? If so, will this compromise the effectiveness of the program?
Many view a particle counter as the most beneficial on-site tool and believe it should be acquired first. The data from this instrument will provide critical information regarding the equipment health and will call attention to associated exception tests when needed. The benefits of having this tool on-site are numerous. Early detection of increased particle levels can be a powerful indicator of both wear and contamination-related problems.
Making the Most of Every Last Dollar
So what is the best approach to on-site analysis with a limited budget? The following is a list of candidate tests that might be preformed on-site:
ISO Particle Count
Moisture Detection Devices
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Karl Fischer Moisture
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Water by Crackle
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Other Water Dectection Devices
Visual Inspection
Soot Detection
Kinematic Viscosity
Elemental Analysis
Acid Number
Voltametry
Dielectric Analysis
FTIR
Foam
Demulsibility
Rust
Ferrous Density
Analytical Ferrography
Ferrography
Fuel Detection
This list we can be reduced by removing tests that are not required on-site because they are seldom performed and/or because the equipment and training costs are exorbitant.
For example, when analyzing a gearbox oil, elemental analysis and FTIR are removed from the on-site analysis list strictly based on the initial costs. Foam, demulsibility and rust tests can also be removed from the on-site list based on the expected limited frequency at which they will be performed.
Also, Karl Fischer moisture involves wet chemistry, which may not be suitable for an on-site lab because chemicals must be handled and a lot of training is required to accurately perform these tests. Because it’s a gearbox, soot and fuel tests are also not needed. The abridged on-site list of tests for a gearbox and the estimated associated costs are illustrated in Table 1.
Click Here to See Table 1.
As the table illustrates, there are several effective ways to utilize even the most modest budget. Given a budget of only $5,000, several tools that will provide significant information regarding lubricant and equipment health can be procured. Tests for water, viscosity, acid number and solid contamination are possible with a $5,000 budget. As the budget increases, so does the arsenal of tools.
Particle Counters
There are several makes and models of particle counters on the market today. Most models are laser-based instruments and a couple are pore blockage (mesh obstruction) instruments. Although most models cost more than $10,000, a particle counter should be at the top of the shopping list when the budget is available. When performing ISO particle counts of any kind, it is crucial for the sample to be violently agitated by an industrial paint shaker. These two items need to be procured at the same time to ensure accurate results.
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Hot Plates
Hot plates are a simple way to identify the presence of water in a system. Hot plates can be procured from any lab supply vendor for as little as $150. This pass/fail method will identify free and emulsified water in the oil and allow the oil analysis practitioner to make educated decisions on necessary exception testing. Because free and emulsified water pose a significant risk to equipment health, a small investment has substantial return potential. This item should be included for purchase in all budget categories.
Viscometers
As with particle counters, there are several viscometers on the market today. There are automatic lab viscometers, simple bench-level viscometers and field-use manual viscometers. Manual viscometers such as the viscosity comparitor, allow for a quick comparative measure of a lubricant’s viscosity, but do not provide the same accuracy as more sophisticated instruments.
For low-budget on-site screening, an inexpensive viscometer is a must and can be used to determine if the correct grade of oil is in use. When a larger budget is available, a more accurate lab-style viscometer should be included.
Acid Number Kits
Acid number kits are designed for use by nontechnical individuals in an on-site environment. These kits provide premeasured, nonhazardous reagents in ready-to-use ampoules. Within minutes, an accurate measure of acids in the oil can be recorded. Although accurate, these test kits only approximate lab titration methods such as ASTM D664 and the two should not be compared quantitatively.
Ferrous Density Testers
Ferrous density testers measure ferromagnetic metal debris (iron or steel) in a given sample. Usually reported by an index number, some results are reported as a percentage of the overall particle count of the same sample. Others simply provide a gravimetric concentration such as micrograms per milliliter. Ferrous density testers can be powerful tools for identifying mechanical failures and for prompting exception tests such as analytical ferrography.
Analytical Ferrography
The instruments needed to perform ferrogram analytical ferrography include a slide maker and a microscope. Although different slide makers are available, all produce a glass slide by holding ferrous particles in place with a magnet as the fluid is passed over. Typically, the microscope will have a 100X to 1,000X resolving power with a digital camera to capture ferrogram images.
These items go hand-in-hand and typically carry a large price tag. A significant amount of training and education must accompany a successful on-site ferrography program. These instruments are often left to mature on-site programs with significant resources.
Patch Test Kits
Alternatively, lower cost filtergram makers, also called patch kits, are valuable tools that offer high return on investment when used routinely. They can be used to provide data on contamination concentration and source, and ferrous and nonferrous wear debris. They are similar to analytical ferrography, even with some superior features, and they should be a part of all on-site oil analysis programs of all budget levels. Patch testing can also enable microscopic particle counts in lieu of automatic particle counters.
Water Meters
There are several moisture meters based on different measurement principles on the market today. Some of these instruments measure the relative humidity of water in oil and provide results in percent saturation (or dew point). Regardless of the technology deployed, a reliable means to detect and quantify free and emulsified water is nearly always justified for on-site analysis.
Even the most modest on-site oil analysis budget can provide the resources necessary for significant instrument inclusions. With as little as $5,000, a strategically important part of an oil analysis program can be brought on-site.
The immediate benefit to bringing oil analysis on-site is that machine reliability information is provided as soon as it’s needed. Timely and significant on-site data combined with data from quality commercial laboratories and an entire menu of available routine and exception tests is a recipe for a world-class oil analysis program.
Oil sight glasses work by giving you a real-time snapshot of the oil inside your machinery without having to shut anything down. This live inside look plays a critical role in condition monitoring and early detection.
What Is an Oil Sight Glass?
An oil sight glass is a transparent tube or bowl installed in a tank or reservoir allowing anyone to visually inspect what's happening with the liquid inside the container. An oil sight glass is an all-encompassing term for the different types of sight glasses that we'll discuss below. Common uses and applications for sight glasses prove especially useful for monitoring oil or lubricant quality and quantity inside pipes, tanks and reservoirs. You'll find them on equipment across industries such as:
- Manufacturing plants
- Pharmaceuticals
- Food and beverage
- Bio fuels
- Wastewater treatment plants
- Chemical plants
Sight glasses are commonly found in industries that use pressurized systems like boilers, steam generators, cement production and even breweries. Using a sight glass is a safe way to check the level and quality of the pressurized liquid without needing to open the tank or reservoir. Most modern oil sight glasses offer 360-degree views and are made of acrylic, polyamide and even a new high-performance copolyester that we'll discuss later.
Types of Oil Sight Glasses
Oil sight glasses typically come in some variation of two forms: the bullseye and the columnar. However, with modern technology and ingenuity, companies are starting to manufacture higher-quality sight glasses and level monitors, often with multifunctional components or combining multiple components. We're going to look at five types of common oil sight glasses on the market today, take a look at some state-of-the-art oil sight glass products and see what they can do for you.
- Bullseye sight glasses are made of transparent material like glass, acrylic or polyamide. They are threaded into a port sitting just above the oil level inside the reservoir. Bullseye sight glasses are great for checking the oil level because there is no piping which could give you a false level reading. Traditional bullseye sight glasses offer a flat, transparent viewing window.
- Columnar sight glasses attach to an oil-containing component near the drain port. They're typically made of acrylic or glass and allow visualization of the oil level fluctuating up and down. A columnar sight glass must be able to "breathe" as oil levels fluctuate, so you'll need to connect it to the headspace using a length of pipe or flexible tubing, which in turn is connected to a desiccant breather. It's also important to mark the idle and running oil levels as a reference for when the levels are off.
One disadvantage of a columnar sight glass is that it doesn't clearly show the presence of foam, since the oil entering the columnar is coming from the bottom of the sump, giving air a chance to escape.
- The 3D sight glasses are new and improved bullseye sight glasses. Luneta's 3D sight glass (shown right) is a great example of a modern 3D sight glass. The most obvious difference is that the 3D sight glass offers a 360-degree visual of the oil with a flat front and crosshairs to check the oil level. Most 3D sight glasses are made with glass, acrylic or polyamide. Luneta's sight glass uses a clear copolyester material called Tritan, which gives the 3D sight glass optimal visualization and the highest durability rating of any sight glass on the market.
- Bottom sediment and water (BS&W) bowls are 2-in-1 devices that act as a sight glass and a BS&W bowl, so you can visually inspect the oil and see potential debris and harmful contaminants like water and sediment. Our example shows Luneta's Bowl - a BS&W/sight glass combination made of the same impact-resistant Tritan copolyester as the company's 3D sight glass. The Bowl uses a rare-earth magnetic drain plug to attract wear debris while the machine is running, drawing wear particles to the bottom and letting you easily drain contaminants.
- Condition Monitoring Pods (CMPs) are kind of like an all-in-one oil sight glass thanks to their multi-use functions. Displayed to the right is Luneta's CMP. It has a 3D sight glass offering a 360-degree view so you can check the oil level, color and clarity as well as if there's any foaming, corrosion or wear debris. It also includes a visible magnetic plug inside the glass to capture wear debris and make it easily visible. The sight glass rotates, allowing you to remove the magnetic plug and corrosion indicator for further inspection. In addition, Luneta's CMP includes a built-in sampling valve with an attached pilot tube for live-zone oil sampling. Like the company's other products, the CMP is made of Tritan copolyester.
Benefits of Using an Oil Sight Glass
Today, oil sight glasses are engineered to be stronger than ever and serve as multi-functional tools, so you not only can check and monitor oil levels and detect wear debris but can even draw an oil sample from the same device. The benefits you'll see from using a modern sight glass include:
- Clear and concise oil level monitoring. For optimal oil level monitoring, look for a 3D oil sight glass with crosshairs on a flat front or a columnar sight glass with the proper oil level marked on the tube.
- Clean and concise oil condition monitoring. Products like Luneta's Bowl and CMP help you attract, see and even extract wear debris and other contaminants that may be in your oil for testing.
For example, say you installed an oil sight glass on a tank. Then, during a routine inspection, you noticed foam in the sight glass. Foam in your oil or lubricant results in the reduction of the oil's lubricating properties, eventually leading to system wear and failure. Foam is a symptom of many issues, such as water or solid contamination, mechanical issues causing too much aeration, or lubricant cross-contamination. Without a sight glass, you may not have detected the presence of foam for a while, since you'd have to manually open the tank to look, which would expose the lubricant to more potential contamination.
Oil Sight Glass Installation
Installing a modern oil sight glass should be a relatively simple process revolving around hand-threading the sight glass and tightening with a crescent wrench. If you don't properly install the sight glass, however, your oil readings will be wrong, and depending on whether your machinery is pressurized, the wrong sight glass could spell trouble. So, what do you need to know before installing your oil sight glass?
- Determine whether you're installing a variation of a bullseye or columnar sight glass. The installation location depends on the sight glass type. Bullseye sight glasses are installed in a port right at the oil level. Columnar and BS&W bowls are installed in the drain port.
- If you're using a length of piping to connect the sight glass to the headspace, make sure there are no "goosenecks" or traps in the piping that would prevent oil from moving freely.
- Note and match the recommended temperature ranges and maximum operating pressure requirements with a sight glass that can satisfy those requirements.
Let's look at what the installation of a sight glass might entail using Luneta's Sight Glass as an example. As mentioned earlier, modern sight glasses can be installed fairly quickly, with this one requiring just five steps.
- Apply thread sealant to the threads.
- Hand-thread the sight glass into the port.
- Use the appropriately sized crescent wrench or socket wrench to tighten until the hex nut comes into contact with the port face. If using an O-ring, tighten until the O-ring is compressed.
- Check for leaks.
- Don't overtighten.
Luneta Sight Glass
Luneta Sight Glass Size
1-inch
0.75-inch
0.5-inch
0.375-inch
0.25-inch
Wrench Size
1-5/16
1-1/18
7/8
3/4
5/8
Recommended
Temperature Range
-40°F to 200°F / -40°C to 93°C
Max. Operating Pressure
65 psi/4.48 bar
Oil Sight Glass Comparison
Even though all oil sight glasses serve to accomplish the same goal (monitoring oil level and condition), it's important to compare not only which sight glasses are best for certain applications but also their makeup and manufacturing properties as well. For example, a poor-quality sight glass installed at the bottom of a reservoir has a high risk of incurring impact damage, which could lead to a major oil leak. Conversely, a sight glass that doesn't meet mechanical pressure ratings can spell disaster for high-pressure machines.
Look at the makeup of various oil sight glasses and compare each one's quality. Specifically, consider things like durability, how resistant it is to impact, its chemical resistance and its thermal ratings. Below is a comparison of the most common oil sight glass materials in relation to these factors.
So, how do you know which type of oil sight glass is best for your specific need or application? Machinery Lubrication compares bullseye and columnar sight glasses side by side and rates them from poor to good based on six forms of detection.
Bullseye vs. Columnar Sight Glasses
Best For
Columnar
3D
Bullseye
Oil Level Confirmation
Excellent
Good
Fair
Oil Color Detection
Excellent
Excellent
Fair
Water Emulsion Detection
Good
Excellent
Fair
Aerated Oil Detection
Poor
Excellent
Fair
Foam Detection
Poor
Good
Fair
What to Know Before Buying an Oil Sight Glass
It's critical to understand the environment and operating conditions your sight glasses must be able to withstand. Each situation may have multiple safety parameters to bear in mind, and you don't want your sight glass to be a contributing factor to these risks. Consider the following factors when choosing an oil sight glass:
- Port availability: Take a look at where your ports are located on your tank or reservoir. Do you have a port at or above the oil level? If so, you can use a bullseye- or CMP-style sight glass. If your only access port is the drain port, you'll need a BS&W bowl or columnar sight glass.
- Pressure: Understand the pressure requirements your sight glass will need to prevent high-pressure bursting.
- Impact damage risk: Anything sticking out from a piece of equipment has a greater risk of impact damage. Review each sight glass's impact resistance, durability and wall thickness specifications.
- Process fluid: Make sure you understand what materials the fluid in your reservoir or tank can corrode. Look for a sight glass with an "excellent" chemical resistance rating.
- Normal service temperature: Knowing the maximum temperature at which your machine can operate and how long it can operate at that temperature is important, especially for high-pressure gas equipment. Spikes in pressure usually only happen when the temperature spikes.
- Maintenance and handling: Some brands of sight glasses are easier to install, maintain and handle than others. With modern ingenuity, you should be able to find a sight glass that is simple to install and easy to clean. If the sight glass port is often used for other tasks like sampling or draining, consider a multifunctional sight glass like Luneta's CMP or Hub.
- Oil level fluctuations: If the oil in your tank or reservoir fluctuates significantly, you should factor this into your decision. Bullseye sight glasses are good for gauging the correct oil level if the level stays within the crosshair marking on the glass. However, if the oil level reads high on a bullseye sight glass, there's no way of knowing just how high the level is inside. In this case, a columnar sight glass might prove useful once you've marked the idle and running oil levels on the glass. If you're seeing oil levels above (or below) these marks, you can get a snapshot of just how much oil might be in the tank.
- Past problems: Consider whether there have been past problems you need to monitor. Have you previously had issues with wear debris contaminating your lubricant? If so, make sure you choose a sight glass with a magnetic plug to help attract that debris for testing.
- Hardware requirements: Typically, columnar sight glasses require you to install more hardware because they're externally mounted. Unless there is a breather attached directly to the columnar sight glass, you'll need flexible tubing or a curved piece of pipe to connect it to the headspace. Other hardware requirements might involve creating a port for the sight glass installation if you don't already have one.
Oil Sight Glass FAQs
What are the components of an oil sight glass?
Oil sight glasses generally are made up of a transparent medium (acrylic, polyamide or Tritan copolyester), a unit body and other features. The "glass" or transparent part of the sight glass varies by shape, thickness and size depending on the type of sight glass. The body of the sight glass not only holds the "glass" in place, but it's also designed to manage stress passed onto the "glass." Other features on a sight glass might include an interior wiper to wipe away condensation or a sampling port to draw an oil sample.
What contaminants are captured by a magnetic plug in a sight glass?
Any metal filings and wear debris can be picked up by a magnetic plug. Even iron particles, which normally tend to sink rather than float, have been proven to be captured by magnetic plugs thanks to turbulence and the oil's viscosity suspending the particles.
How do I clean an oil sight glass?
Use warm water and soap. Cleaning products containing ammonia or alcohol can cause cracking, which leads to staining and weakening.
For more information, please visit Oil Condition Monitoring System.
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