A Roots-type positive displacement blower moves air by trapping it between two counter-rotating figure-eight rotors and pushing it toward the discharge — no valves, no compression inside the casing. What kills them is what you ignore: climbing discharge temperatures, rising differential pressure, a gear case running low, a belt that's been glazed for three months. The rotors don't touch the casing by design — but they can, once enough things go wrong.
This checklist covers the recurring PM tasks for Roots-type PD blowers in standard industrial and pneumatic conveying applications.
For a broader look at how blowers and fans fail and what your PM program should be doing about it, see industrial fan and blower PM programs and the failure modes they target.
⚠️ Disclaimer: These tasks are guidelines only. They do not include lockout/tagout (LOTO), energy isolation, or other safety requirements. Review and verify suitability for your specific equipment and application. Add all required safety procedures per your company's policies and regulatory requirements before use. You are responsible for the safe and appropriate execution of all maintenance activities.
How to Use This Checklist
Record actual readings, not checkmarks. "Discharge temp: 237°F" is useful. "✓" is not. The value of this checklist compounds over time — a single reading tells you where you are; six readings tell you where you're going.
Trend everything you can measure. Discharge pressure, gear case temperature, vibration — if you're not watching how these numbers move over successive PMs, you're reacting to failures instead of catching them.
A bad finding looks like this: "Gear case oil: milky, changed." That is a root cause investigation, not a checkbox. Milky gear oil means water contamination. Find the source before the next PM or you'll be writing the same note again.
A good finding looks like this: "Drive-end gear case temp: 174°F — up from 161°F last quarter. Belt tension verified in spec. Oil changed. Trending."
Field Checklist — Critical Tasks
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect blower casing exterior for cracks, corrosion, oil leaks around end plates and seals, and any unusual residue. | Every PM | MEC |
| Inspect discharge silencer, piping, and check valve for leaks, corrosion, or physical damage. | Monthly | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Listen for abnormal noise during operation — grinding, knocking, or high-pitched squealing may indicate rotor contact, bearing wear, or foreign object ingestion. | Every PM | MEC |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Check inlet filter/silencer for excessive restriction, damage, or clogging. Clean or replace filter element as needed. | Monthly | MEC |
| Inspect drive belt(s) or coupling for wear, cracking, glazing, or misalignment. Verify belt tension is within specification. | Monthly | MEC |
| Check blower mounting hardware — base bolts and anti-vibration mounts. Tighten any loose fasteners. | Quarterly | MEC |
| Inspect shaft seals at both ends for oil weeping or air leakage. Flag any seal showing active leakage for replacement. | Semi-Annually | MEC |
Lubrication
| Task | Freq | Type |
|---|---|---|
| Check oil level in both drive-end and non-drive-end gear cases. Top off with correct grade if low. Note any discoloration or milky appearance indicating contamination. | Monthly | MEC |
| Change gear case oil in both end housings per manufacturer's oil change interval. Use specified oil grade. | Semi-Annually | MEC |
Reference Checklist — Full Task Library
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect blower casing, end plates, and inlet/discharge flanges for cracks, corrosion, oil weeping, or air leaks. Note any residue indicating a chronic leak point. | Every PM | MEC |
| Inspect discharge silencer, flex connectors, piping, and check valve for leaks, corrosion, or physical damage. Verify check valve operates freely without sticking. | Monthly | MEC |
| Inspect shaft seals on both drive-end and non-drive-end for oil weeping or air leakage. Distinguish between minor seepage (monitor) and active leakage (replace). Note that oil in the air stream indicates end seal failure. | Monthly | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Listen and feel for abnormal noise or vibration during operation — knocking, grinding, or squealing can indicate rotor-to-rotor contact, bearing deterioration, or timing gear wear. Flag immediately if rotor contact is suspected. | Every PM | MEC |
| Measure and record blower inlet and discharge pressure (or vacuum and pressure differential). Compare to baseline. A rising differential without process changes may indicate rotor wear or bypass leakage. | Every PM | MEC |
| Check blower operating temperature at the discharge port and gear cases using a contact thermometer or IR gun. Record readings and compare to historical baseline. Investigate if discharge temp exceeds 250°F or gear case temp exceeds 180°F. | Every PM | MEC |
| Measure and record motor operating current and voltage with blower running under normal load. Compare to nameplate and historical baseline. Rising current at constant pressure may indicate internal rotor drag. | Quarterly | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect and clean inlet filter/silencer element. Measure differential pressure across the filter if a gauge is installed. Replace element if clogged, damaged, or at manufacturer's recommended interval. | Monthly | MEC |
| Inspect drive belt(s) for wear, cracking, fraying, or glazing. Verify tension and alignment. Check sheave/pulley condition. Misalignment or improper tension accelerates bearing and gear wear. | Monthly | MEC |
| Check blower mounting bolts, base plate, and anti-vibration isolators. Tighten any loose fasteners and inspect isolators for compression set, cracking, or deterioration. | Quarterly | MEC |
| Inspect timing gear condition by removing the gear case cover if accessible. Look for pitting, spalling, or abnormal tooth wear patterns. Confirm gear backlash is within manufacturer's tolerance. | Quarterly | MEC |
| Verify blower-to-driver alignment (belt/sheave or direct coupling). Check angular and parallel alignment. Correct as needed. Misalignment is the leading cause of premature bearing and seal failure on PD blowers. | Semi-Annually | MEC |
| Inspect rotor clearances on units with accessible end plates. Verify axial and radial rotor-to-casing clearances are within manufacturer's specification. Document readings for trending. | Annually | MEC |
| Review and trend all recorded data from this PM cycle — discharge pressure, temperatures, vibration, current draw, and oil condition. Compare to previous PM records. Flag any worsening trends for engineering review. | Annually | MEC |
Lubrication
| Task | Freq | Type |
|---|---|---|
| Check oil level in drive-end and non-drive-end gear cases. Inspect oil condition — discoloration, milkiness, or metallic sheen requires immediate oil change and root cause investigation. | Monthly | MEC |
| Inspect drive-end and non-drive-end bearings. On units with grease-lubricated bearings, regrease per manufacturer's interval and type. Do not over-grease. On oil-lubricated units, verify oil feed and return. | Quarterly | MEC |
| Change gear case oil in both end housings. Use oil grade specified by the manufacturer (typically ISO VG 150 or 220 — verify on nameplate or manual). Inspect drained oil for metal particles before disposal. | Semi-Annually | MEC |
Vibration Measurement
| Task | Freq | Type |
|---|---|---|
| Perform vibration measurement at drive-end and non-drive-end bearing housings using a vibration pen or analyzer. Record overall velocity (in/s or mm/s) and compare to baseline trend. Investigate any step-change increase. | Quarterly | MEC |
Failure Modes This Checklist Targets
Timing Gear Wear and Failure The timing gears synchronize the two rotors so they counter-rotate without touching. When gears wear, backlash increases — and rotor-to-rotor contact becomes a real possibility. Oil condition and gear case temperature are your early indicators.
Rotor-to-Casing Contact Roots blowers rely on tight internal clearances to move air efficiently. Rotor contact with the casing or with each other generates immediate noise, heat, and catastrophic mechanical damage. The check for abnormal noise at every PM exists specifically to catch this before the casing tells you itself.
Bearing Degradation Both end-housing bearings — drive-end and non-drive-end — carry the radial and axial loads of the rotor shafts. Misalignment, over-greasing, contaminated oil, and thermal cycling all accelerate wear. Vibration trending and oil inspection are the practical PM tools here.
Inlet Filter Restriction A restricted inlet filter starves the blower of air, raises discharge temperature, increases differential pressure, and puts mechanical stress on the rotors and seals. It's one of the most preventable failure contributors on any PD blower — and one of the most commonly skipped checks.
Shaft Seal Failure End seals keep gear oil in and process air out. When they weep, you lose oil. When they fail, oil enters the air stream — and if that air is going into a pneumatic conveying system, the problem reaches further than the blower room. Oil-contaminated seals showing active leakage don't get monitored; they get replaced.
Drive System Misalignment and Belt Wear A misaligned sheave or glazed belt puts uneven radial loads on the shaft bearings, accelerates gear wear, and shortens seal life. The belt looks fine until it doesn't — check tension and alignment every PM cycle, not just when you hear the squeal.
