When we operate rotary screw compressors, our main focus is often on pressure, flow, and uptime. However, one issue we can’t ignore is oil carryover. Even a small amount of oil leaking into downstream systems can create problems. From damaging tools to contaminating products, oil carryover can lead to expensive downtime and repairs. Therefore, understanding the causes behind it helps us take the right steps to fix it early.
In this post, we’ll walk through what oil carryover actually is, why it happens, and what we can do to reduce it. We’ll also offer practical advice from our team at Air Compressors Canada so you can keep your system clean and efficient.
What Is Oil Carryover and Why It Matters
Oil carryover refers to the presence of lubricating oil in the compressed air output. It’s not just a small annoyance. In other words, it can ruin air lines, damage pneumatic equipment, and cause product contamination in sensitive industries.
Most rotary screw compressors are oil-injected, meaning oil is used for sealing, cooling, and lubrication. However, if the system isn’t working properly, some of that oil can escape into the compressed air system. Subsequently, that contamination travels downstream and leads to more serious issues.
Separator Filter Efficiency Plays a Key Role
One of the biggest causes of oil carryover is a worn or inefficient separator filter. This component is designed to remove oil from the air before it exits the compressor. That is to say, the filter traps oil mist and allows it to return to the sump.
When the separator becomes saturated or clogged, it simply can’t do its job anymore. Consequently, oil bypasses the filter and enters the air stream. We recommend checking the separator’s pressure differential regularly. If it gets too high, usually above 10 psi, it’s a sign the element needs to be replaced.
You can find more practical compressor advice from our industrial air compressor supplier resource, which covers maintenance insights and supply support.
Inlet Air Quality Can Affect Oil Levels
The air coming into your compressor matters more than we think. If dust, mist, or fumes are entering through the inlet, those contaminants can mix with the oil inside the compressor. As a result, oil viscosity changes, which makes it harder for separators to remove it from the air.
To clarify, this doesn’t mean every system needs a high-end filtration setup. But we should install and maintain basic inlet filters and make sure the compressor is in a clean location. Placing it too close to other industrial machines can lead to contamination we wouldn’t expect.
Oil Return Line Issues Are Easy to Miss
Most oil-injected rotary screw compressors have an oil return line that sends collected oil from the separator back to the main sump. However, when this line gets blocked or damaged, the oil has nowhere to go. Therefore, it gets pushed into the compressed air path instead.
We often see this when maintenance has been delayed or replacement parts aren’t installed correctly. In addition, if the line is routed too high or uphill, gravity can’t assist in returning the oil efficiently. That small design detail can make a big difference.
To keep your compressor setup efficient, our guide on how compressors work and what affects performance offers tips you won’t often see in standard manuals.
Excess Oil Fill Can Lead to Higher Carryover
We know it’s tempting to top up compressor oil to the brim during routine service. However, overfilling is a common cause of excess carryover. The system is designed to operate with a precise oil level. Therefore, when it’s too high, oil can foam, mist, and travel with the air.
Similarly, using the wrong oil type can also affect this balance. We should always match the viscosity and formulation to manufacturer recommendations. Using a thicker or incompatible oil may lead to poor separation and more contamination downstream.
Temperature Imbalances Inside the System
Compressors need to operate within a specific temperature range. If things run too hot or too cold, the oil properties change and separators stop working as intended. For example, oil becomes thinner at high temperatures, making it harder to separate from air.
On the other hand, running the system too cool can create condensation that mixes with oil and turns it into an emulsion. Consequently, this mixture doesn’t separate properly and leads to visible carryover. Maintaining good ventilation and monitoring oil temperature regularly helps avoid this issue.
Drain and Piping Issues After Compression
Even if the main separator filter is working well, oil can still accumulate in air receivers or piping after the compressor. This often happens when automatic drains fail or aren’t installed at key collection points. For instance, elbows and low points in piping tend to trap oil mist and condensate.
Over time, that buildup re-enters the air flow during pressure surges. Therefore, regular inspection and drain maintenance are critical, especially in humid environments or where demand fluctuates rapidly.
Monitoring the System Over Time
We always recommend setting up a regular oil analysis schedule. This helps detect early signs of oil degradation or contamination before carryover becomes visible. Likewise, tracking the pressure drop across separators, filters, and dryers helps identify blockages early.
Many systems now allow digital monitoring of these components. But even in smaller facilities, a manual logbook that tracks separator hours, oil changes, and filter replacements can prevent long-term issues.
If you’re unsure how to create a basic maintenance schedule, our team can help. For custom help or troubleshooting tips, reach out to us directly through our contact page and we’ll respond quickly.
One Extra Tip: Don’t Ignore Drain Valve Settings
A useful insight we often share is related to drain valve programming. Many systems use electronic timed drains, which open based on a preset timer. However, if those settings don’t match the real condensate volume, oil can accumulate between drain cycles.
For example, if your system generates more condensate during the summer, the drain interval needs to be adjusted. Otherwise, the oil will pool and travel downstream. Switching to a demand-activated drain system is usually more efficient and can significantly cut carryover without any major hardware change.
FAQs About Oil Carryover in Compressors
1. How can I tell if my compressor has oil carryover?
You may notice oily residue at air tool connections, staining around hoses, or a strong odor in the compressed air. These are all signs that oil is bypassing your separator.
2. Does using synthetic oil reduce carryover?
In many cases, yes. Synthetic oils are more stable at varying temperatures and tend to resist foaming, which helps reduce carryover. Still, the rest of the system must be in good condition for best results.
3. How often should I replace the separator element?
Most separators need replacement every 2,000 to 4,000 hours, but that depends on air quality and system load. Monitor the pressure drop and consult the manual for specific guidance.
4. Can carryover affect air dryers or filters?
Absolutely. Excess oil can clog dryers and downstream filters quickly, leading to pressure drop and inefficient drying. It can also reduce the lifespan of those components.
5. What’s the best way to prevent carryover in older compressors?
Start with routine inspection of the separator, return lines, oil type, and drain systems. Keep detailed maintenance records and consider retrofitting better separators or drains if needed.