Reliability-centred maintenance for compressed-air systems

What is reliability-centred maintenance, in plain terms?

Most compressor maintenance in Indian plants is built on the manufacturer’s service schedule: change the oil, air and oil filters and separator at set hours, check belts, clean coolers. That schedule is a sensible starting point, but it was written for an average machine in average conditions. It does not know that your compressor room reaches 45 °C in May, that cement dust reaches the intake, or that a two-hour air outage stops a packing line worth far more than the compressor.

RCM starts from the other end. It asks seven practical questions for each part of the system:

1. What function must it perform, and to what standard (for example, 7 bar at the header, pressure dew point of +3 °C, oil carry-over within the required ISO 8573-1 class)?
2. In what ways can it fail to perform that function?
3. What causes each failure (the failure mode)?
4. What happens when it fails – locally, across the system and in the process?
5. Why does it matter – safety, quality, production, energy, cost?
6. What task can predict or prevent it, and is that task worth doing?
7. If no task is worth doing, what then – run to failure, redesign, standby or spares?

The output is not a thicker manual. It is a short list of justified tasks for each asset, each with a reason, an interval or trigger, and an owner.

Start with functions, not machines

A compressed-air system is a chain: intake, compressor, aftercooler, receiver, dryer, filters, drains, piping and point-of-use regulation, plus the controls, cooling and ventilation that keep them working. The plant does not care about the compressor; it cares that air arrives at the right pressure, flow and quality whenever it is needed.

So write functions in measurable terms:

• Supply: deliver the required free air delivery (FAD) at the required pressure at the critical users, not just at the compressor discharge.
• Quality: hold the required pressure dew point, particle and oil levels for the application – far tighter for pharma, food or instrument air than for general workshop air.
• Containment: keep pressure safely contained in receivers, separators and piping.
• Protection: shut the machine down safely on high temperature, overload or low oil.
• Efficiency: deliver air within an acceptable specific power, without excessive leaks or pressure drop.

Once functions are written down, a functional failure becomes obvious: “header pressure falls below 6 bar during second shift” is a failure even if every compressor is running.

Common compressed-air failure modes and what detects them

The table below lists failure modes we see repeatedly on oil-injected screw compressors and their auxiliaries in Telangana and Andhra Pradesh plants, with the task that is usually effective. Your own list should come from your machines’ history.

Hidden failures: the ones that hurt most

Some components only matter when something else goes wrong. A safety relief valve, a high-temperature trip, a standby compressor, an auto-changeover and a dryer bypass alarm all sit quietly until they are needed. If they have failed, nobody notices – until the day they are called on.

RCM treats these differently. You cannot predict their failure by watching them run, so the right task is a failure-finding test: deliberately check that the protection works. Examples:

• Start the standby compressor on load at a set frequency, not just “bump” it.
• Verify high discharge temperature and overload trips against their settings during service.
• Have relief valves tested or replaced as the manufacturer and applicable rules require.
• Test the automatic sequencing or changeover by simulating loss of the lead machine.

Pressure equipment such as receivers is also subject to statutory inspection; RCM never replaces that, it simply makes sure it is in the plan.

How to decide which task is worth doing

For each failure mode, choose from a short menu, in roughly this order of preference:

1. Condition-based task: if the failure gives warning (vibration, temperature, differential pressure, oil condition), monitor it and act on a threshold. Most airend, separator, cooler and filter problems fall here.
2. Scheduled restoration or replacement: if the failure is age-related and gives little warning, replace on hours. Oil, filters and separators on hire or very dusty duty often suit this, because condition checking costs more than the part.
3. Failure-finding: for hidden protective functions, as above.
4. Run to failure: acceptable where failure is evident, cheap, safe and has no production consequence – a non-critical point-of-use regulator, for example – provided the spare is on the shelf.
5. Redesign: if no task reduces the risk enough – a single compressor feeding a critical process, a dryer with no bypass, a compressor room with no ventilation – change the system.

A task is worth doing only if it is technically able to catch or prevent the failure and its cost is lower than the consequence it avoids. Many inherited tasks fail this test: “check everything” rounds with no recorded readings, or blanket replacement of parts that are in good condition.

Operating context in Indian plants changes the answer

The same compressor needs a different plan in different places. Factors we account for in Telangana, Andhra Pradesh and across India:

• Summer ambient heat: compressor rooms in Hyderabad and coastal Andhra commonly run well above design ambient in April–June. Cooler condition, ventilation and discharge-temperature margin become the dominant risk.
• Dust: cement, mining, foundry, construction and borewell sites load intake filters and coolers far faster than the standard schedule assumes.
• Humidity and monsoon: coastal sites and monsoon months raise condensate volumes, so drains, dryers and oil water content need closer attention.
• Power quality: voltage dips and frequent restarts stress motors, starters and contactors.
• Duty pattern: lightly loaded machines that start and stop often can collect condensate in the oil; machines on 24-hour duty wear by hours far sooner.

On our own hire jobs with portable diesel compressors on round-the-clock duty, for example, we service machines and change the oil every 300 running hours because the duty and environment justify it, an interval chosen for the context, not copied from a brochure.

Link RCM to criticality

Do not analyse every drain valve with the same effort as the main compressor. Rank assets first by consequence of failure, then apply RCM depth accordingly:

This keeps the effort proportionate and makes the plan easy to explain to management.

A practical RCM review, step by step

1. Define the boundary: which compressors, dryers, receivers, filters and main lines are included.
2. Collect history: service records, breakdowns, trip logs, running and load hours, oil reports, power bills.
3. Write functions and performance standards with the people who use the air.
4. List failure modes per component, from history and engineering experience.
5. Rate consequences and decide criticality.
6. Select tasks using the menu above, with intervals or condition thresholds.
7. Set spares and standby strategy for failures you cannot prevent.
8. Issue the plan as work orders and simple log sheets.
9. Review after each failure and at least yearly: did the task catch it? If not, change the task.

The last step is what makes RCM a living system. A plan that is never reviewed slowly drifts back into calendar maintenance.

What to record so the plan works

RCM depends on evidence. A minimum log for a screw compressor installation:

• Running hours and load hours, weekly.
• Discharge pressure, discharge temperature and ambient room temperature, daily.
• Separator and filter differential pressures where gauges or controllers show them.
• Dryer pressure dew point.
• Oil top-ups with quantity and date.
• Trips and alarms with cause found.
• Oil analysis and vibration readings, where used.

Without readings, every decision falls back to guesswork and the calendar.

How Reddy Compressors helps

Reddy Compressors has been serving industry since 2002 from Tarnaka, Secunderabad. As an independent multi-brand specialist we work on Atlas Copco, Ingersoll Rand, ELGi, KAESER, Chicago Pneumatic, Gardner Denver, Sullair, Doosan, Kirloskar, Bobcat and many other machines, so the plan we help you build is neutral and covers the whole air system, not one brand’s equipment.

• Site review of compressors, dryers, filters, receivers, drains and piping, with a criticality ranking.
• A practical failure-mode and task list for each critical asset, with log sheets your operators can actually fill.
• Service and AMC delivery against that plan, including condition checks, oil sampling, consumable replacement and failure-finding tests.
• Breakdown repair and overhaul when failures do happen, with the findings fed back into the plan.
• Air audits and leak surveys to tie reliability to energy cost.
• Spare parts identified from the nameplate and old part, with fit confirmed before quoting, so critical spares can be stocked with confidence.

Our service teams cover the whole of Telangana and Andhra Pradesh, and we supply equipment, rental compressors and spares across India. Call +91 99590 60718 or +91 92468 88812, or email reddycompressors@gmail.com.

What to send us

• List of compressors and dryers with make, model, serial number and nameplate photos.
• Running and load hours, and the current service schedule.
• Breakdown and trip history for the last one to two years, if available.
• Which processes use the air and what an outage costs or affects.
• Required pressure and air quality at critical users.
• Photos of the compressor room, ventilation and air treatment.

Frequently asked questions

Is reliability-centred maintenance worth it for a small compressor plant?

Yes, in a scaled-down form. A plant with two or three compressors does not need a formal study, but it benefits from the same questions: which machine is critical, what usually fails, what warning do we get, and what is a test that proves the standby works. Even an afternoon spent on this often removes useless tasks and adds the one or two checks that prevent the next costly outage.

Does RCM mean I can ignore the manufacturer’s service schedule?

No. The manufacturer’s schedule, warranty conditions and statutory inspections remain the baseline. RCM adjusts around them using your operating context: shortening intervals where heat, dust or duty demand it, adding condition monitoring where it gives warning, and adding failure-finding tests for protective devices. Any extension of intervals beyond the manufacturer’s recommendation should be backed by evidence such as oil analysis and trend records.

What is the difference between preventive maintenance and RCM?

Preventive maintenance is a set of tasks done at fixed intervals. RCM is the method used to decide which tasks belong in that set and why. An RCM-based plan still contains preventive tasks, but each one is linked to a specific failure mode and consequence, and it is mixed with condition-based tasks, failure-finding tests, run-to-failure decisions and occasional redesign where no maintenance task can reduce the risk enough.

Which compressor failures give early warning signs?

Many of the expensive ones do. Airend bearing wear usually shows as rising vibration and wear metals in the oil. Cooler fouling shows as discharge temperature creeping up, especially in summer. Separator blockage shows as rising differential pressure. Leaks show as rising load hours at steady production. Logging these readings regularly gives you time to plan a repair instead of facing a breakdown.

How often should a standby compressor be run?

The right frequency depends on the machine and site, but the principle is that a standby is a hidden function and must be proved, not assumed. Run it on load long enough to reach normal operating temperature, check pressures, drains and trips, and record the result. Rotating duty between machines on a planned basis is often the simplest way to keep every unit exercised and evenly worn.

Can you build an RCM plan for compressors of different brands?

Yes. Reddy Compressors is an independent multi-brand specialist, so we routinely work on mixed installations with machines from several manufacturers. The method is the same regardless of brand: functions, failure modes, consequences and justified tasks. We use each manufacturer’s published requirements as the baseline and add tasks based on your operating conditions and records.

Related pages

• Compressed-air criticality classification and service levels
• Predictive and condition-based maintenance
• Building a preventive maintenance plan
• Compressor oil analysis and fluid condition
• Compressor vibration monitoring
• Compressor annual maintenance contracts