Roots Blower Lubrication: A Comprehensive Guide

The reliable operation of a three-lobe Roots blower is paramount for numerous industrial processes, from pneumatic conveying to wastewater aeration. Ensuring its longevity and stable performance hinges significantly on a robust and consistent maintenance schedule, with lubrication being a cornerstone of this strategy. Neglecting proper lubrication can lead to premature wear, increased friction, overheating, and ultimately, costly downtime. This guide will delve into the critical aspects of lubricating your Roots blower, covering recommended intervals, oil types, viscosity considerations, and best practices for both traditional and the Roots Universal RAI® series.

Understanding Roots Blower Lubrication Needs

Roots blowers, renowned for their robust design, rely on precise lubrication to maintain the integrity of their moving parts. The core principle is to reduce friction between the meshing lobes and the blower casing, as well as to cool critical components such as bearings. The type of lubrication and its frequency are dictated by the specific model and operating conditions.

General Maintenance and Lubrication Schedule for Three-Lobe Roots Blowers

For a standard three-lobe Roots blower, regular maintenance is key. Here’s a breakdown of common recommendations:

• Initial Oil Change: After the first 6 months of operation, it is crucial to replace the oil. Keep meticulous records of this service.
• Regular Oil Top-Up: During daily production inspections, monitor the oil level. If it appears low, replenish the lubricant promptly to maintain the correct level.
• Post-Overhaul Oil Change: Following any significant overhaul of the blower, a complete lubricant replacement is necessary after the initial 8 hours of operation.
• Oil Level Observation: Regularly clean the oil level observation mirror. This allows for a clear visual check to ensure there is no oil deficiency.
• Bearing Temperature: Monitor bearing temperatures. They should not exceed 85℃ for optimal performance and to prevent premature wear.
• Oil Temperature: The lubricating oil temperature should not surpass 65℃. Exceeding this limit can degrade the oil and reduce its effectiveness.
• Pressure Monitoring: Always ensure that the pressure within the blower system does not exceed the specifications listed on the nameplate. If the pressure limit is breached, immediately stop the fan and investigate. Potential causes include blockages in the inlet, closed inlet/exhaust valves, or friction issues between static and dynamic parts. Promptly address any identified problems.
• Transmission System Inspection: Regularly inspect and maintain the blower's transmission system. This includes checking the belt for tension and wear. Replace the belt if it shows signs of wear to prevent slippage or failure.
• Electrical Component Checks: Periodically inspect the electrical parts, including the motor and control system. Ensure that all connections, wiring, and components like cables, wiring, and switches are in good condition and free from wear.

Always refer to the manufacturer's instruction manual for specific details pertaining to your model. While these are general guidelines, site-specific conditions may necessitate adjustments to the maintenance schedule.

Lubrication for Roots Universal RAI® Blowers

The Roots Universal RAI® series, and indeed many other Roots products, have specific lubrication requirements that ensure their long operational life. Proper lubrication is not merely about filling a reservoir; it's about using the correct type and viscosity of lubricant tailored to the operating environment.

Drive End vs. Gear End Lubrication

The Roots Universal RAI® series uniquely utilises grease on the drive end and oil on the gear end. The majority of other Roots products, however, employ oil for both the gear and drive ends.

Oil Lubrication Best Practices

When it comes to oil lubrication, several factors are critical:

Synthetic vs. Petroleum-Based Oils

Synthetic lubricants generally offer superior performance and longer intervals between oil changes compared to petroleum-based products. They are highly recommended wherever practical. The ideal oil should be:

• Premium grade
• Non-detergent
• Contain rust, oxidation, and foam inhibitors

ROOTS™ Synthetic Oil is the manufacturer's recommended lubricant. It boasts high oxidation stability, excellent corrosion protection, extremely high film strength, and a low coefficient of friction. This translates to oil change intervals that can be 2-3 times longer than those for petroleum-based lubricants. Importantly, ROOTS™ Synthetic Oil is 100% compatible with petroleum-based oils, meaning you can simply drain the old oil and refill with the synthetic alternative to optimise performance.

Oil Viscosity Selection

The correct oil viscosity is directly dependent on the ambient temperature surrounding the blower and its driver. It is crucial to note that 'ambient temperature' refers to the temperature of the space where the blower is located, not the external air temperature.

Splash Lubricated Blowers

Pressure Lubricated Blowers

*Important Note: For ambient temperatures below 32°F (0°C), the oil must be heated to 60°F (15.6°C) prior to starting the blower to ensure proper flow and lubrication.

Oil Change Intervals

The initial oil change for all Roots products should occur after the first 100 hours of operation. For petroleum-based oils, the normal life expectancy is approximately 2000 hours at an oil temperature of around 180°F (82°C). However, for every 15-18°F (8-10°C) increase in oil temperature above this, the oil's life expectancy is halved.

With ROOTS™ Synthetic Oil, the expected life expectancy is significantly extended, typically ranging from 4000 to 8000 hours at an oil temperature of about 180°F (82°C). Similar to petroleum oils, for every 15-18°F (8-10°C) rise in oil temperature, the effective lifespan of the synthetic oil is also reduced by half.

Estimating Oil Temperature

A useful estimation for oil temperature can be made by multiplying the discharge temperature of the air or gas stream by 0.8. For instance, if the blower's discharge air temperature is 200°F (93.3°C), the estimated oil temperature would be around 160°F (71.1°C).

Grease Lubrication for Roots Universal RAI® Blowers

For the Roots Universal RAI® blowers that utilise grease on the drive end, the type of grease used is critical:

• Older Units: Historically, manuals recommended a clay-based Shell Darina grease for general use. It's important to note that Shell has since replaced Darina grease with Gadus grease. For gas applications, a NLGI Grade 2 premium grade aluminum complex grease was advised.
• Newer Units (from Fall 2016 onwards): Roots standardised to using synthetic grease on all units. If your unit has a serial number starting with '16' followed by a letter, it will use the purple Roots synthetic grease.

Crucially, the two types of grease – clay-based and synthetic – cannot be mixed. Mixing them can lead to separation, compromising their lubricating properties and potentially damaging the blower.

Frequently Asked Questions

How often should I lubricate my Roots blower?

For general three-lobe Roots blowers, replace oil every 6 months or after an overhaul (8 hours of operation). Monitor oil levels daily. For Roots Universal RAI® series, consult the manual, but synthetic oils generally allow for longer intervals. Initial oil change is after 100 hours.

What is the recommended oil for Roots blowers?

ROOTS™ Synthetic Oil is the recommended premium lubricant for its superior properties. If using petroleum-based oils, ensure they are non-detergent and have appropriate inhibitors.

Can I mix different types of grease in my Roots blower?

No, absolutely not. Never mix clay-based greases with synthetic greases, as this will cause them to separate and lose their lubricating effectiveness.

What is the maximum safe oil temperature for a Roots blower?

The lubricating oil temperature should not exceed 65°C (149°F) for general maintenance. For specific performance expectations and oil life, an oil temperature of around 180°F (82°C) is often cited, but higher temperatures significantly reduce oil life.

How do I determine the correct oil viscosity?

Oil viscosity depends on the ambient temperature of the blower's location. Refer to the tables provided in this guide for splash-lubricated and pressure-lubricated blowers, matching the ambient temperature to the recommended ISO Viscosity Number.

By adhering to these lubrication guidelines and performing regular maintenance, you can significantly enhance the lifespan and operational efficiency of your Roots blower, ensuring reliable performance for years to come.