Step 4 of 10: Cleanliness Control
Four gates stand between the drum and the bearing.
Four gates stand between the drum and the bearing.
Contamination doesn't wait for the machine to age — it's carried in at every handover between storage, transfer, the reservoir and the point of use. Close each gate properly and the oil that reaches the component is the oil you paid for.
WHY CLEANLINESS COMES BEFORE EVERYTHING ELSE
MOST "OLD MACHINERY"FAILURES ARE DIRTY-OIL FAILURES
Contamination is one of the most common causes of premature equipment failure. Dust, water, metal shavings and degraded oil don't need to be visible to do damage — the particles that cut bearing surfaces and score gear teeth are almost always smaller than the eye can resolve.
Once contaminants are inside a system they are difficult to remove and expensive to fix. Keeping lubricant clean from the moment it leaves the refinery to the moment it enters a bearing is one of the simplest, cheapest reliability interventions available — but it only works if every handover in the chain is treated as a control point, not just the obviously dirty ones.
"Our oil looks clean. Why filter it?"
Visual clarity tells you almost nothing. The particles that cause the most wear — in the 4 to 14 micron range — are invisible to the naked eye, and even new oil from a sealed drum can carry contamination picked up in transport or storage. Filtration isn't a response to dirty oil; it's a precondition for using any oil at all.
THE FOUR CONTROL GATES
Three of these stages will be familiar from any lubrication programme. The reservoir and its breather are usually left out — and it's often where the most contamination gets in during normal operation.
01 = Storage | Keep it sealed and organised
01 = Storage | Keep it sealed and organised
Before the oil ever moves, the container is the barrier.
- Use closed, weatherproof storage units for oils and greases.
- Label and colour-code every container to prevent mix-ups.
- Protect stored lubricant from humidity, temperature swings and airborne dust.
- Inspect and clean storage areas on a fixed schedule, not only when something looks wrong.
Often missed
New oil from a sealed drum is rarely clean enough for a precision component straight out of the box. Treat delivery as the start of the contamination-control chain, not the end of it.
02 = Transfer | Keep it clean, keep it controlled
02 = Transfer | Keep it clean, keep it controlled
Every open funnel undoes what storage protected.
- Use dedicated transfer containers with sealed lids and built-in filtration.
- Avoid open funnels, buckets or improvised tools entirely.
- Assign specific equipment to each lubricant type to prevent cross-contamination.
- Cap every hose and nozzle the moment it's not in use.
Often missed
Cross-contamination between compatible-looking oils (two ISO VG 46 hydraulic oils from different suppliers, for example) is still contamination — additive packages don't always mix cleanly.
03 = Reservoir & breathing
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Control what the machine breathes in
03 = Reservoir & breathing |
Control what the machine breathes in
The reservoir keeps taking in air for as long as the machine runs.
- Fit desiccant breathers to reservoirs, gearboxes and hydraulic tanks — a standard vent draws in dust and moisture with every thermal cycle.
- Check and replace breather cartridges on condition, not just on a calendar.
- Inspect seals, gaskets and sight glasses for the slow leaks that let water and dirt track in.
- Track moisture separately from particle count: a "dry" reading can mask water already dissolved in the oil.
Guide moisture limits
Keep free water at zero tolerance and dissolved water below roughly 50% relative saturation for turbine and hydraulic oils — tighter for high-value or water-sensitive assets. Confirm exact limits with your lubricant supplier, since they vary by base oil and additive chemistry.
04 = Application | Filter before and during use
04 = Application | Filter before and during use
The last gate is the one closest to the component you're protecting.
- Pre-filter all oil before it enters the machine, even when it's new.
- Install offline (kidney-loop) filtration on critical machinery for continuous polishing.
- Use online particle counters for continuous monitoring of critical assets, and portable counters or lab sampling for the rest.
- Train staff on contamination control at the point of use — the best filtration cart in the world doesn't help if the fill point is left open.
Often missed
Not all filters rated to the same micron size perform the same. Efficiency is described by the beta ratio, not the pore size on the label — see below.
HOW CLEAN IS CLEAN ENOUGH
SET A TARGET CLEANLINESS CODE - DON'T GUESS AT ALL
ISO 4406 describes cleanliness as three numbers, each representing the number of particles per millilitre at ≥4, ≥6 and ≥14 microns. Lower numbers mean fewer particles and cleaner oil. These are typical starting points — always confirm final targets with your OEM or reliability engineer.
TYPICAL ISO 4406 TARGET CODES BY ASSET TYPE
A code is only useful if you're actually measuring against it. Pair each target with a monitoring method — inline particle counter for continuous critical assets, portable counter for spot checks, laboratory analysis for trending over time.
CHOOSING A FILTER
MICRON RATING TELLS YOU THE HOLE SIZE. BETA RATIO TELLS YOU IF IT WORKS
ISO 4406 describes cleanliness as three numbers, each representing the number of particles per millilitre at ≥4, ≥6 and ≥14 microns. Lower numbers mean fewer particles and cleaner oil. These are typical starting points — always confirm final targets with your OEM or reliability engineer.
A filter rated β10 ≥ 1000 removes 99.9% of particles at 10 microns and larger. A filter rated β10 = 2 removes only half. Both can be sold as "10 micron" filters — always ask for the beta ratio, not just the pore size.
The root cause, most of the time
Industry field studies consistently attribute a large majority of hydraulic and lubrication-related component failures to contamination — and most of that contamination is introduced during storage, transfer and maintenance activity, not generated by the machine itself. Closing the four gates is a handling discipline, not a hardware purchase.
Clean oil is the cheapest insurance policy your equipment will ever own.
— Industrial maintenance engineering practice
Define target cleanliness levels for every asset class before the next oil change.
Define target cleanliness levels for every asset class before the next oil change.