Compressor root-cause analysis and corrective action

Why replacing the part is not the end

When a compressor fails, the first priority is to restore air safely, often with a repair or a rental machine. But replacing a failed bearing, separator or motor only closes the repair. If the reason it failed is still present, the new part will follow the same path. Repeated failures of the same kind are the clearest sign that the cause was never found.

Consider a screw compressor bearing. It can fail through lubrication starvation, oil contamination by dust or water, overheating, misalignment of the drive, excessive load from high discharge pressure, electrical current passing through the bearing on some VSD installations, incorrect fitting or simply age. Each of these needs a different corrective action. Guessing wrong costs a second airend.

The language of a good investigation

Clear terms prevent arguments and wrong conclusions.

Step-by-step root-cause method

1. Stabilise and preserve – restore air safely, but keep failed parts, oil samples and filter elements. Do not throw away the evidence with the scrap.
2. Build the timeline – last known healthy state, first abnormal sign, alarms and trips with timestamps, operator observations, recent maintenance, part changes, lubricant changes and process changes.
3. Collect evidence – controller logs, service records, oil analysis, photographs of failed parts in the as-found state, temperatures, pressures, vibration readings and ambient conditions.
4. List competing hypotheses – every plausible mechanism, not just the first one mentioned.
5. Test each hypothesis – against the evidence and the manufacturer’s limits. Which ones explain all the facts? Which are contradicted?
6. Identify the system cause – ask why the condition existed and why existing checks did not catch it.
7. Decide corrective and preventive actions – specific, owned, dated.
8. Verify effectiveness – check later that the change was made and that the failure has not recurred.

Confidence should be stated honestly. If an oil sample was not taken, say so; a hypothesis remains a hypothesis until evidence supports it.

Common compressor failures and their usual mechanisms

Normal discharge temperature on oil-injected screw compressors is typically about 75–95 °C. Sustained operation above that range accelerates oil oxidation, which then shows up as varnish, blocked separators and stuck valves months later. The temperature problem, not the varnish, is often the real starting point.

Evidence: what to keep and how

• Failed parts as found – photograph them before cleaning. A cleaned bearing tells far less than a dirty one.
• Oil sample – taken from the system before draining, in a clean bottle, labelled with hours and date. Our oil analysis page explains what the results show.
• Filters and separator – keep the used elements; dust on the clean side of an intake element or damage to a separator is valuable evidence.
• Controller data – alarm history, running hours, loaded hours and starts, downloaded before anyone resets or changes settings.
• Service records – what was done, when, with which parts and oils.
• Site conditions – room temperature, ventilation, dust, recent building changes or new machines nearby.

Getting to the system cause

A physical mechanism almost always has a human or organisational reason behind it. Asking “why” repeatedly, while testing each answer against evidence, moves from the part to the system. Typical system causes we see:

• Service intervals set by calendar when the compressor runs far more hours than planned.
• Non-matching oil or parts used because the correct item was not identified from the nameplate.
• Compressor-room conditions changed by additions or building work without a ventilation review.
• Pressure raised to compensate for leaks or undersized pipework, increasing load and temperature.
• Alarms reset repeatedly without investigation.
• No baseline readings, so slow deterioration was not noticed.

Corrective actions that actually work

An action list should be short, specific and checked. Strong corrective actions change the condition itself: improving ventilation, correcting the oil specification, fixing alignment, changing service triggers to running hours, adding a baseline and trend. Weak actions rely on people remembering, such as “operators to be more careful”. Each action needs an owner, a date and a check that it was done. Where a failure has damaged the airend, our airend condition and overhaul decision page explains how we decide between repair, rebuild and replacement.

Prevention: making the next investigation easier

The best root-cause analysis is the one you never need because the deterioration was caught early. Three habits make a large difference. First, record a baseline after every service or overhaul: discharge temperature, pressures, motor current, filter and separator differential pressure and vibration where measured. Second, trend those readings over time so that a slow rise is visible long before a trip. Third, keep a simple log of every change to the machine or its surroundings, including oil brand, parts source, pressure set points and room layout. When something does fail, the timeline and the evidence are already there. Our condition monitoring and baseline work and AMC visits are built around exactly these habits, and they apply equally to stationary screw, piston and portable diesel machines.

How Reddy Compressors helps

Based in Tarnaka, Secunderabad, with more than 20 service engineers and technicians serving all of Telangana and Andhra Pradesh, and supplying equipment and spares across India, we:

• Attend breakdowns, restore air safely and preserve failed parts, oil and filters as evidence.
• Inspect failed components, review controller logs and service history and arrange oil analysis.
• Build a timeline and test competing causes against the evidence and the manufacturer’s limits.
• Recommend corrective actions on the machine, the compressor room and the maintenance routine.
• Carry out repairs, overhauls and airend rebuild support; specialist processes such as rotor regrinding or coating are arranged where needed.
• Provide rental compressors from our own fleet while a failed machine is investigated and repaired.

We work on ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar, Gardner Denver and many other brands as an independent specialist, not an authorised dealer. We have tie-ups with all major and reputed brands.

What to send us

• Compressor make, model, serial number, nameplate photo and running hours.
• A description of what happened and when, with any alarm or trip messages.
• Photos of the failed parts as found, before cleaning.
• Recent service records, oils and parts used.
• Whether this or a similar failure has happened before.
• Compressor-room conditions: temperature, ventilation and dust.

Frequently asked questions

Why does my compressor keep failing in the same way?

Because the condition that caused the first failure is still there. Replacing a bearing, separator or motor repairs the damage but does not remove the cause, whether that is hot intake air, contaminated or wrong oil, misalignment, overload or a missed service trigger. A root-cause investigation looks at the evidence and the operating history to find and remove that condition.

What causes screw compressor airend bearing failure?

Common mechanisms are lubrication starvation, oil contaminated with dust or water, overheating from high discharge temperatures, overload from high pressure, drive misalignment and, on some VSD installations, electrical current through bearings. Age and incorrect fitting also play a part. The bearing surface, oil analysis and the machine’s temperature and service history usually show which mechanism was responsible.

What evidence should I keep after a compressor breakdown?

Keep the failed parts uncleaned, a labelled oil sample taken before draining, used filters and the separator, and download the controller alarm and running-hours history before resetting anything. Photographs of the as-found condition and notes from operators about what they saw and heard are equally valuable. Without this, the investigation relies on memory.

What is the difference between failure mechanism and root cause?

The failure mechanism is the physical process that damaged the part, such as abrasive wear or oil oxidation. The root or system cause is the reason that process was allowed to happen, such as an intake filter that was not sealed properly or service intervals set by calendar instead of running hours. Fixing the mechanism alone rarely prevents recurrence.

Why does my compressor oil turn black quickly?

Fast darkening usually points to high operating temperature, which oxidises the oil, or to contamination from dust bypassing the intake filter. Mixing incompatible oils or overextending change intervals can also cause it. Oil analysis, intake filter inspection and a check of discharge temperatures and room ventilation normally reveal which factor is responsible.

Can you investigate a failure on a compressor of any brand?

Yes. As an independent multi-brand specialist we investigate failures on ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other brands. We follow the manufacturer’s published limits for the machine and base our conclusions on the evidence we can collect from the failed parts, oil, logs and site conditions.

Related pages

• Breakdown diagnostics, fault triage and recovery
• Troubleshooting and diagnostic engineering
• Compressor lubricant and oil analysis
• Airend condition and overhaul decisions
• Compressor vibration monitoring
• Preventive maintenance architecture