Roots Blower Maintenance: A Practical Preventive Maintenance Checklist for Maximum Uptime

Why Preventive Maintenance Matters for Roots Blowers

A roots blower runs with very close clearances between the two counter rotating lobes and between the lobes and the casing walls. These clearances, typically 0.1 to 0.4 millimetres depending on the machine size, are maintained by precision timing gears that synchronise the two shafts without any direct contact between the lobes themselves. If the timing gears lose lubrication, the clearances change, and the lobes make contact, which causes immediate and severe damage.

Similarly, the bearings that support the two rotor shafts carry both radial and axial loads from the gas pressure differential. Bearing failure causes rotor runout that quickly leads to lobe contact. Neither gear failure nor bearing failure gives much warning before catastrophic damage occurs, which makes planned preventive maintenance far more cost effective than reactive repair.

Daily Checks (Every Operating Day)

Visual and instrument checks

• Check blower discharge temperature. Normal operating temperature for an air cooled machine is typically 60 to 100 degrees Celsius above ambient at the design differential pressure. A rise of more than 15 degrees above the established normal indicates a problem
• Check discharge pressure against the process requirement. A significant rise indicates a blocked filter or system restriction. A significant drop indicates a leak or worn lobes
• Listen for unusual sounds. A roots blower running normally produces a regular rhythmic pulsation noise. A beating or whirring sound at a frequency different from the rotor frequency indicates a bearing issue. A metallic knocking indicates lobe contact
• Check oil sight glass on gear end cover to confirm oil is at the correct level and is not milky or discoloured
• Inspect inlet air filter indicator if fitted and clean or replace filter element if the vacuum drop across the filter has reached the replacement threshold

Weekly Checks

• Check all pipe flanges and casing joints for air leaks using soapy water solution. Any bubbles at a joint should be addressed promptly
• Verify that the pressure relief valve is not leaking or weeping, which indicates it may be set too low relative to the normal operating pressure

Monthly Checks

Lubrication and oil analysis

• Check gear end oil level and top up as required with the specified oil grade. Most Acme roots blowers use ISO VG 220 gear oil in the timing gear housing. Check the machine manual for the correct specification for your model
• Check bearing housing oil level on drive end and non drive end bearings where separately lubricated bearing housings are fitted
• Check oil for evidence of contamination. Metallic particles in the oil indicate gear or bearing wear. A milky appearance indicates water ingress, which commonly occurs when a machine is shut down in a humid environment and condensation forms inside the casing
• Inspect inlet filter element and replace if differential pressure across the filter exceeds the manufacturer’s specification. Blockage of the air inlet is one of the most common causes of overheating and reduced performance

Three Monthly Checks

• Measure vibration velocity at each bearing location using a hand held vibration meter. Record the values as a trend. ISO 10816 guidelines for machines of this type specify that vibration velocity should not exceed 2.8 millimetres per second RMS for new machines and 4.5 millimetres per second for machines in service. Rising vibration trend is the most reliable early warning of bearing deterioration
• Check shaft seal condition on the blower casing. Lip seals or mechanical seals separating the gas side from the gear and bearing lubricant should not be leaking oil into the gas stream or allowing gas to migrate into the gear housing

• Inspect the discharge silencer if fitted. A blocked silencer increases back pressure on the blower. Check that the discharge silencer drain valve is open and functioning
• Verify motor current draw and compare with the nameplate rating. Current significantly above the nameplate value at the normal operating conditions indicates mechanical overloading

Annual Overhaul

Full inspection and component replacement

• Drain and replace timing gear oil completely. Clean the gear housing sump of any accumulated metallic debris. Inspect gear tooth condition and gear clearances before refilling
• Remove and inspect bearings at annual service. Replace bearings according to the calculated L10 bearing life from the manufacturer’s documentation, regardless of apparent condition. Bearing life at rated speed and load is typically 25,000 to 40,000 operating hours
• Measure lobe clearances using feeler gauges or dial indicators at the four standard measurement positions for the machine size. Compare with the factory clearance specification. Clearances that have grown beyond 150 percent of the original value indicate lobe or casing wear
• Inspect inlet filter housing and filter element mounting seats for corrosion or distortion that could allow unfiltered air to bypass the element
• Check and re torque all foundation bolts and pipework flanges
• Record all measurements in a machine history file for trend analysis at the next annual service

Warning Signs That Indicate Immediate Attention

The following signs should cause immediate investigation and, if necessary, shutdown:

• Sudden rise in discharge temperature of more than 25 degrees above the established normal
• Metallic knocking or scraping sound that was not present previously
• Smell of burning oil from the gear housing or bearing areas
• Unusual vibration that has appeared suddenly rather than gradually
• Oil leakage from shaft seals onto the blower casing
• Discharge pressure consistently higher than normal operating values, which may indicate a system blockage loading the blower beyond its design pressure

Frequently Asked Questions