Greentech International (Zhangqiu) Co., Ltd.
In industries such as pneumatic conveying, wastewater treatment, and powder conveying, the Roots blower is a core piece of equipment for the entire production line. Its operational stability directly affects whether production can proceed continuously. However, during daily maintenance, lubricating oil emulsification is a common and recurring fault in Roots blowers. Many field technicians have encountered issues such as the gearbox oil turning white and cloudy, oil foaming, high oil temperature, and abnormal gear noises. This article, based on over 20 years of on-site commissioning and maintenance experience, systematically explains the real causes of oil emulsification, the resulting equipment damage, and practical prevention methods.
Roots blower gearboxes commonly use L-CKC 220 medium-load gear oil. Under normal conditions, the oil is translucent reddish-brown, has good fluidity, and contains no foam or impurities.
Color Change: The oil turns milky white, grayish-white, or turbid yellow. In severe cases, it looks like milk.
Abnormal Physical State: The oil becomes thinner, generates foam, contains floating flocculent matter, and the oil level appears inexplicably high.
Water at the Bottom: After standing, water accumulates at the bottom of the housing.
Operational Abnormalities: Oil temperature exceeds 80°C, increased vibration, abnormal gear noise during operation. Prolonged neglect can lead to high bearing temperatures and abnormal wear.
Many people initially think that poor oil quality is the cause. However, the vast majority of emulsification problems are caused by water or moisture entering the gearbox. Once moisture enters the housing, the high-speed rotation of the gears agitates the mixture, breaking the water into tiny droplets that mix with the oil, forming a stable emulsion – the "white oil."
Common causes of water ingress include:
The skeleton oil seals at both ends of the gearbox are critical components that prevent oil leakage and block moisture ingress. They are wear parts. After 1-2 years of use, these seals can harden, crack, and wear out. In humid conditions, wastewater mist, ambient moisture, or rainwater can seep into the gearbox along the shaft gap. Additionally, loose seal covers, aged O-rings, or incorrectly installed oil seals can also lead to poor sealing.
The breather vent on top of the gearbox equalizes internal and external pressure. However, the vast majority of original breathers do not contain desiccant; most are sintered copper or stainless steel mesh filters that only block dust, not moisture. In high-humidity environments such as outdoor operation in rain, wastewater treatment plants, or the humid "hui nan tian" season in southern China, moist air enters the housing directly. When the equipment is shut down or during large temperature differences between day and night, this moisture condenses into liquid water. The next time the blower starts, the gears churn the oil-water mixture, quickly causing emulsification.
Desiccant breathers with blue silica gel are aftermarket optional add-ons, not standard factory equipment. They are only needed in specific humid conditions.
The oil filler cap, oil sight glass, housing flange faces, and cover joints all have gaskets. Long-term high-temperature operation and vibration can cause these gaskets to age, crack, or detach. For outdoor units or those washed down regularly, rainwater or wash water can directly enter the gearbox. Some older or poorly cast housings may have fine cracks or porosity, which can also allow slow water ingress and accumulation of condensate.
If a desiccant-type breather is installed, the desiccant must be checked regularly. Standard blue indicator silica gel turns pink after absorbing moisture, losing its effectiveness. Whether a standard breather or a desiccant type, if it becomes clogged with dust or oil, the blower can develop internal pressure during operation, which can push out oil seals and cause leaks. Conversely, when the blower cools down during shutdown, negative pressure can draw external moisture into the housing.
Wastewater, chemical, and powder handling plants have high ambient humidity. Standard breathers continuously draw in moist air, which condenses over time. Frequent starts and stops or intermittent operation cause the housing temperature to cycle, repeatedly generating condensate that cannot drain on its own. Blowers left outdoors without rain protection are more prone to water ingress.
Adding oil outdoors on rainy days, using wet refilling tools, or storing spare oil improperly can introduce water. Overfilling the oil level increases the load on the gears from churning, and oil temperatures that consistently exceed 80°C significantly reduce the oil's demulsibility. Mixing different brands or types of gear oil with incompatible additives can also destabilize the oil and promote emulsification.
Some technicians believe that the blower can still "run for a while" with white oil. This is a serious mistake. Emulsified oil completely loses effectiveness, and its lubrication and protective properties are severely degraded. Long-term operation in this condition causes irreversible damage:
Oil Film Failure: Gears and bearings lose lubrication, leading to dry friction, gear pitting, wear, and bearing seizure. In severe cases, the shaft can break, causing a shutdown.
Accelerated Component Wear: Parts such as gears and bearings fail much sooner, significantly increasing repair costs.
Production Line Interruption: Excessive vibration, noise, or sudden bearing seizure will halt the blower and shut down the entire production line.
Regularly Inspect Seals: Replace shaft oil seals and various gaskets as soon as they show aging, cracking, or hardening. Ensure the seal cover is tight and the seal is correctly seated during installation.
Choose the Right Breather:
Dry indoor conditions: Use the original dust-proof breather and clean it periodically.
High-humidity plants, outdoor use, intermittently running blowers: Consider installing a desiccant breather. Check the silica gel color monthly; replace or regenerate (dry) the gel when it turns from blue to pink.
Standardize Oil Refilling and Daily Management:
Avoid adding oil outdoors on rainy days. Keep refilling tools and stored oil dry.
Maintain the oil level at the middle of the sight glass. Keep operating oil temperature below 80°C.
Always use the same brand and type of oil. Do not mix.
Other Protections: Install a rain cover for outdoor units. Before long-term shutdown, replace the oil with fresh oil and seal the breather and any other openings to reduce moisture ingress.
1. Stop the blower immediately and disconnect power. Drain all emulsified oil from the housing.
2. Clean the housing:
3. For mild emulsification: Flush with new oil.
4. For severe water ingress with obvious standing water: Disassemble the housing to completely drain water and remove sludge.
5. Thoroughly inspect all seals: Replace any worn, damaged, or aged oil seals, gaskets, and flange seals.
6. Inspect and clean the breather: Clear any blockages in standard breathers. Replace depleted desiccant in desiccant breathers.
7. Refill with new oil and test run: Fill with new gear oil of the same specification to the correct level. Run unloaded for 30 minutes. Observe oil temperature, vibration, and gear noise. If normal, return to production.
The root cause of oil emulsification in Roots blowers is simply moisture or water entering the gearbox, combined with agitation from the rotating parts. In practice, aging oil seals and condensate from high-humidity environments are the two primary triggers. Harsh operating conditions and improper maintenance only accelerate the failure.
It is important to note: Desiccant breathers are optional accessories, not standard factory equipment. Choose them based on actual operating conditions, and do not install them unnecessarily.
If you encounter issues such as oil emulsification, abnormal noise, high oil temperature, or need guidance on pneumatic conveying system modifications or equipment maintenance, please feel free to reach out for targeted on-site solutions.
Roots Blower product information
Web: http://www.greentechblower.com (Group Web) ‖ http://www.zqblower.cn (Chinese) ‖ http://www.ringblower.cn/ (Ring blower) ‖ http://www.china-blower.com (Roots Blower)
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