October 27, 2026
Posted by: editor
Category: RECD & Emission Control Devices

A cleaning shop has quoted a fraction of the price of a new element. Or your supplier has offered a reconditioned unit as a stop-gap. Or a used device you are evaluating comes with a “freshly serviced” filter inside. Whichever route brought you here, the question is the same: will a refurbished RECD filter core actually do its job on your DG set, and will it keep you compliant?

The short answer is sometimes. It depends on what was done to the core, what condition it is in now, and whether the device as refitted still matches its type-approved configuration. A core that was properly cleaned, inspected, documented and re-sealed can give useful further service. A core that was simply blown out with a compressed-air gun in a workshop yard is a gamble.

Below, we clear away the common myths, then set out an inspection-and-acceptance protocol.

Myth vs fact: what owners get wrong about reused filter cores

Myth 1: “Cleaned means as good as new”

Fact: Cleaning removes deposits. It does not reverse wear. Where the core is a wall-flow ceramic filter, every cleaning removes most of the soot and a large share of the ash, but some ash usually stays bonded in the channel ends and pores. Thermal cycling over hundreds of hours can also create micro-cracks, and any catalyst coating may have lost activity. A well-cleaned core may come close to its original back-pressure, but “close” is the honest word. The only way to know how close is to measure it, which is why the acceptance protocol later in this post matters.

Myth 2: “If it looks clean, it works”

Fact: The inlet face of a filter can look spotless while plugs are cracked, channels are partly blocked deeper in, or the substrate has a hairline fracture that lets exhaust bypass the filtering walls. Visual appearance tells you almost nothing about filtration efficiency. Flow testing, weighing and a crack inspection tell you far more. A core that leaks through a crack will often show lower back-pressure than a healthy one, which can mislead an untrained eye into thinking it is in excellent shape.

Myth 3: “Any cleaning shop can do it”

Fact: Filter cleaning is a specialised process. The right bake-out temperature, ramp rate and dwell time depend on the substrate material and on any coating. Over-aggressive heating can crack ceramic; unsuitable water or chemical cleaning can damage some substrates or strip catalyst; compressed air at the wrong pressure or from the wrong direction can drive ash deeper rather than remove it. Ask what equipment and method they will use on your specific core, and whether your RECD supplier approves that method.

Myth 4: “A refurbished core keeps the original certificate automatically”

Fact: Type approval applies to a defined device configuration. Whether a cleaned or refurbished core, refitted into the same housing, is still treated as that configuration is a question for your RECD supplier and, where needed, your State Pollution Control Board. A re-manufactured core, a core from a different device, or one with replacement seals or mats of unknown specification may raise questions. Do not assume. Get it in writing, and keep the paper with your compliance file. Our guide on reading an RECD test certificate explains what the certificate actually covers.

Myth 5: “Refurbishing is always cheaper”

Fact: The invoice for cleaning is usually lower than a new core. The total cost may not be. Add removal and refit labour, transport both ways, downtime, new gaskets and mats, a post-refit test, and the risk that the core fails early and you end up buying new anyway. In some cases a refurbished core is clearly the better deal; in others it only defers a purchase you cannot avoid. The illustrative cost comparison later in this post shows how to frame it.

Cleaning, refurbishment, re-manufacture and replacement: the definitions

These words are used loosely on quotes and invoices. Pin them down before comparing offers.

Term	What it typically involves	What it does not address	Why it may matter for warranty and type approval
Cleaning	Removing soot (usually by thermal bake-out) and ash (usually by pulsed air) from the existing core	Cracks, damaged plugs, worn seals or mats, catalyst condition	Often treated as routine maintenance, but confirm the method is acceptable to your supplier
Refurbishment	Cleaning plus documented inspection, flow testing, and renewal of wear parts such as gaskets, seals or support mats	Substrate replacement, coating renewal	Replacement wear parts should match the original specification; ask the supplier whether this keeps the configuration intact
Re-manufacture	Substantial rebuild, which may include re-canning, replacing the substrate or re-coating	Nothing, in principle, but quality depends entirely on the re-manufacturer	Most likely to change the configuration; confirm in writing before fitting
Replacement	A new core from the device manufacturer or an approved source	Not applicable	Usually the clearest route for warranty and configuration, but confirm part numbers match

If you are still deciding whether to change just the core or the whole unit, our sibling post on replacing an RECD filter core versus the complete assembly walks through that choice in detail.

What happens in a typical RECD filter cleaning and refurbishment process

Methods vary between providers and between core types, so treat this as a generic outline, not a specification. Ask your provider to describe their own steps in writing.

1. Pre-inspection and weighing

The core arrives, is photographed, and its serial number or identification is recorded. It is weighed in its as-removed state. If the provider has, or you supply, the new-condition mass, the difference tells you roughly how much soot and ash it is carrying. The inlet and outlet faces are inspected for face plugging, oil wetting, discolouration and visible cracks.

2. Pre-clean flow or pressure-drop test

A flow bench pushes a controlled volume of air through the core and measures the pressure drop across it. This gives a “before” value under repeatable conditions, independent of the engine.

3. Thermal bake-out

Where the substrate allows it, the core is heated in a controlled kiln or oven to oxidise the soot slowly. The aim is to burn off carbon without the sudden temperature spikes that can crack ceramic. This is broadly the same chemistry as regeneration on the engine, but done under controlled conditions; DieselNet’s overview of particulate filter regeneration is a good technical primer if you want the background.

4. Ash removal

Ash, unlike soot, does not burn. It comes mostly from lubricating oil additives and wear metals, and it accumulates in the filter over its life. It is typically dislodged with pulsed air, often blown in the reverse direction to normal exhaust flow, and collected. DieselNet’s page on ash in diesel particulate filters explains why ash builds up and why it is the long-term limit on filter life. Some providers use water or chemical cleaning instead or in addition. These methods may not suit every substrate or coating, so ask the supplier of your RECD before agreeing.

5. Post-clean flow test and weighing

The flow test is repeated under the same conditions, and the core is weighed again. Comparing before and after figures shows how much material was removed and how close the core is to its new-condition baseline.

6. Visual and crack inspection

The faces are inspected again. A common practical method is a light test: a bright light is shone through individual channels or across the face to spot cracks, broken plugs or channels that let light pass where they should not. Some providers use more sophisticated inspection. The point is to find leaks that would let soot slip past.

7. Wear-part renewal (refurbishment only)

Gaskets, seals, clamps and support mats may be replaced. These parts matter: a perished mat can let the substrate move inside its can, and a failed gasket lets exhaust bypass the filter entirely.

8. Report

A good provider issues a written report covering everything above, with numbers, photos and the core’s identification. That report is the foundation of your acceptance decision.

When reusing a cleaned RECD element makes sense

Reuse is a reasonable option when most of the following are true:

The core has a known history: you know which DG set it came from, roughly how many running hours it has, and how many times it has been cleaned before.
It was removed because of gradual soot and ash loading, shown by a slow rise in back-pressure, not because of a sudden failure.
The engine it came from was in reasonable health, with normal oil consumption and no coolant leaks.
The cleaning provider’s method is acceptable to your RECD supplier.
Post-clean flow results are close to the new-condition baseline.
No cracks, melted areas or broken plugs were found.
The supplier confirms in writing that refitting the cleaned core keeps the device in its approved configuration.

The RECD maintenance guide covers how this fits into routine servicing.

When a cleaned core should not be reused

Some conditions mean the core should be retired regardless of how clean it looks.

Cracks or fractured plugs. These create leak paths. Filtration efficiency drops, sometimes sharply, and cleaning cannot fix them.
Melted or fused channels. Usually the result of an uncontrolled regeneration after heavy soot loading. The damaged area is permanently lost and stress around it can spread.
Oil or coolant saturation. A core soaked by a failing turbo seal, worn rings or a head gasket leak can be contaminated beyond what thermal cleaning recovers, and the underlying engine problem will repeat the damage. Our post on how engine oil consumption affects RECD suitability explains the link.
Catalyst poisoning. If the core carries a catalytic coating, contamination from high-sulphur fuel, oil additives or coolant can reduce its activity. Cleaning removes deposits but may not restore the coating.
Repeated cleaning cycles exhausted. Each cleaning leaves a little residual ash and puts the core through another thermal cycle. Ask the supplier whether there is a recommended limit on cleanings or a residual-ash threshold beyond which the core should be retired.
Unknown history. If nobody can tell you where the core came from, how it was used or how many times it has been cleaned, you are accepting all of those risks blind.
Mismatched identity. A core that does not match the part number or dimensions of your device should not be fitted, however good the price.

Worked example: reading the numbers from a cleaning report

The following example is illustrative. The figures are invented to show how to interpret a report; your own core’s values will differ.

Mass balance

Measurement	Mass (kg)
New-condition core (from supplier data)	18.0
As removed from the DG set	19.6
After cleaning	18.3

From these figures:

Total accumulated deposit before cleaning = 19.6 − 18.0 = 1.6 kg
Material removed by cleaning = 19.6 − 18.3 = 1.3 kg
Residual deposit after cleaning = 18.3 − 18.0 = 0.3 kg
Residual as a share of new mass = 0.3 ÷ 18.0 × 100 = 1.67%, roughly 1.7%
Removal efficiency = 1.3 ÷ 1.6 × 100 = 81.25%

So the cleaning removed a little over four-fifths of what had built up. The 0.3 kg left behind is most likely bonded ash, which is normal to some degree. What you want to know from the supplier is whether 0.3 kg residual on an 18.0 kg core is within their acceptable range, and how much more residual the core can tolerate across future cleanings.

Back-pressure on the engine

After refitting, back-pressure is measured at the same stated load used for the original baseline, 75% load in this illustrative case.

Condition	Back-pressure at 75% load (kPa)	Change from baseline
Baseline (core new, at commissioning)	4.0	Reference
Before cleaning	7.2	(7.2 − 4.0) ÷ 4.0 × 100 = +80%
After cleaning and refit	4.4	(4.4 − 4.0) ÷ 4.0 × 100 = +10%

The cleaned core is running about 10% above its new-condition baseline. That is consistent with the residual mass result. Whether +10% is acceptable depends on the DG manufacturer’s back-pressure limit and the RECD supplier’s guidance. The more important reading is that the core did not come back below baseline: a significantly lower-than-new value after cleaning would be a warning sign of a crack or bypass leak. If you need the background on why these numbers matter to the engine, see how exhaust back-pressure affects a DG set.

Note the condition “at the same stated load”. A back-pressure figure without a matching load is almost meaningless, which is why the guidance on matching generator load in RECD comparison tests applies just as much here.

Illustrative cost comparison

Again, these figures are illustrative and will vary widely by core size, location and provider.

Cost item	Refurbish existing core	Fit new core
Core supply or cleaning service	₹38,000	₹3,20,000
Gaskets, seals and mats	₹14,000	Included
Transport to and from cleaning provider	₹9,000	Not applicable
Removal and refit labour	₹12,000	₹12,000
Total	₹73,000	₹3,32,000

Refurbishment saves ₹3,32,000 − ₹73,000 = ₹2,59,000 on paper. But if the refurbished core fails acceptance or fails early, you pay both: ₹73,000 + ₹3,32,000 = ₹4,05,000, plus a second round of downtime. The saving is real only when the acceptance evidence is strong. This is why the documents in the next section are not paperwork for its own sake.

The acceptance protocol for a refurbished RECD filter core

Split acceptance into two stages: document acceptance before the core comes back to site, and site acceptance after it is refitted.

Stage 1: documents to demand before refitting

Ask for these in writing. If a provider cannot or will not supply them, treat that as a finding in itself.

Identity and traceability. Serial number or unique identification of the core, matching your device records, with photos showing the marking.
Cleaning provider details. Company name, address and the name of the person responsible for the work.
Process description. The steps performed, including bake-out temperature profile and ash-removal method, and whether any water or chemical cleaning was used.
Before and after weights. As-received and as-dispatched mass, with the new-condition mass if known.
Flow or pressure-drop results. Before and after values measured on the same bench at the same flow, with units stated.
Crack and plug inspection. Method used and result, with photos of both faces.
Wear parts renewed. List of gaskets, seals or mats replaced, with part identification showing they match the original specification.
Cleaning history. How many times this core has been cleaned before, as far as is known.
Supplier confirmation. A written statement from your RECD supplier that the cleaned or refurbished core, refitted as described, keeps the device in its approved configuration and does not affect warranty, or a clear statement of what it does affect.

Record dates in an unambiguous format on all of these; the ISO 8601 format (YYYY-MM-DD) avoids confusion between day-month and month-day conventions when reports pass between organisations.

Getting the core to and from the cleaner safely

Ceramic substrates are vulnerable to impact and vibration in transit. A core that leaves your site intact and arrives cracked has been ruined by logistics, not by cleaning. Our sibling post on packaging and transporting an RECD without damaging its internals applies equally to a core travelling on its own. Photograph the core and packaging at dispatch and on receipt, both ways.

Removing and refitting a core means working on a hot, heavy exhaust component. Isolate the DG set with proper lockout and tagout before work starts (OSHA’s page on controlling hazardous energy is a useful reference for the principles), allow full cool-down, and use rated lifting equipment for cores that cannot be safely handled by hand.

Stage 2: site acceptance after refit

Once the core is back in its housing:

Leak check. With the engine running at light load, check every flange, clamp and gasket joint for exhaust leaks. Soot tracking around a joint is a classic sign. Any leak upstream of the filter is a bypass.
Warm-up. Bring the engine to stable operating temperature before taking readings.
Back-pressure at stated load. Measure at the same load point used for your original baseline. Compare as in the worked example above.
Opacity or smoke check. A visible-smoke or opacity reading downstream of the RECD gives a quick indication that the filter is filtering. It is not a substitute for a particulate mass test; our explainer on smoke opacity versus particulate mass sets out the differences.
Optional PM test. If the core’s history is uncertain, if the supplier asks for it, or if your consent conditions require periodic testing, consider a particulate matter test. Plan it properly using the approach in planning a before-and-after RECD emissions test, and work out the result as shown in how to calculate RECD particulate reduction. Use a laboratory with appropriate accreditation; NABL’s site lets you check accredited testing laboratories.
Sensor and controller check. If your RECD has differential pressure or temperature sensors, or a controller, confirm the readings make sense with the cleaned core and that any alarm thresholds are still appropriate.
Record and file. Enter the results in your RECD logbook with the core’s serial number, the date and the name of the person who carried out the check.

A reuse scorecard you can use

Use this table to make a structured decision. Any single “Fail” should normally stop reuse. Several “Conditional” results together are also a reason to lean towards a new core.

Criterion	Pass	Conditional	Fail
Core identity	Serial matches device records	Serial unreadable but dimensions and part number match	Does not match device
History	Hours and previous cleanings known	Partly known	Unknown
Reason for removal	Gradual loading	Uncertain	Sudden failure, oil or coolant event
Cleaning method	Documented and approved by RECD supplier	Documented, approval pending	Undocumented
Residual deposit	Within supplier’s stated limit	Close to limit	Above limit
Flow test after cleaning	Close to new-condition value	Moderately above new	Well above new, or suspiciously below
Crack and plug inspection	No defects	Minor cosmetic marks, explained	Cracks, melted or broken plugs
Wear parts	Renewed to original specification	Reused but inspected	Missing or unknown specification
Supplier confirmation	Written, configuration unchanged	Verbal only	Refused or not sought
Back-pressure after refit	Close to baseline at stated load	Moderately above baseline	Far above, or well below, baseline
Opacity or smoke check	Normal for a working RECD	Borderline	Visible smoke

Keep the completed scorecard with the provider’s report.

Compliance and warranty: who carries the risk?

However the core was cleaned and by whom, the DG set owner remains responsible for compliance. CPCB requires that RECDs used on in-use DG sets be type approved, with at least 70% particulate matter capture efficiency demonstrated during testing by recognised agencies; see the CPCB website for official notifications. Your SPCB consent conditions, and in Delhi NCR the directions of the Commission for Air Quality Management, govern how you may operate. If an inspector finds a DG set running with an RECD that is not performing, or in a configuration that cannot be shown to be approved, the consequences can include sealing and penalties. Our post on what happens during a pollution control board inspection describes what inspectors typically look for.

On warranty, check your RECD contract before sending the core anywhere. Some warranty terms may exclude damage caused by unapproved cleaning, or by parts not supplied by the manufacturer. Our guide to RECD warranty terms, parts, labour and exclusions covers what to look for. If something goes wrong after a refurbished core is fitted, the records you collected under the acceptance protocol become your evidence; the sibling post on what to record when raising an RECD warranty claim explains how to present them.

If your cleaning is being arranged by a service company other than the original supplier, read whether a different service company can maintain an installed RECD before you sign anything. And if the refurbished core is coming with a complete second-hand device, the broader risks are covered in whether buying a used RECD is a sensible option.

Never run the DG set with the core removed, or with a bypass fitted, while waiting for a cleaned core to return. That is a compliance risk, not a workaround. If downtime is a concern, plan the cleaning around a period when the DG set is not needed, or discuss a temporary arrangement with your supplier.

FAQ

Can a refurbished RECD filter core be as effective as a new one?

It can come close if the core is undamaged, properly cleaned and refitted with correct seals. It is rarely identical, because some residual ash usually remains. Measure back-pressure and, if needed, particulate reduction to confirm performance.

How many times can an RECD filter core be cleaned?

There is no universal number. It depends on the substrate, how much residual ash builds up with each cleaning and the core’s thermal history. Ask your RECD supplier whether they set a limit or a residual-ash threshold.

Does cleaning an RECD filter core affect its type approval?

Cleaning that keeps the original core and configuration is often treated as maintenance, but this is for your supplier to confirm in writing. Re-manufactured or substituted cores are more likely to raise configuration questions.

Is water or chemical cleaning safe for RECD filter cores?

Not for every substrate or coating. Some cores are cleaned only by thermal bake-out and pulsed air. Ask your RECD supplier which methods are acceptable before agreeing to any process.

What is the quickest sign a cleaned core is damaged?

Back-pressure noticeably below the new-condition baseline at the same load, or visible smoke downstream, both suggest a crack or bypass leak. A crack inspection should be part of every cleaning report.

Should I accept a refurbished core without a cleaning report?

No. Without before-and-after weights, flow results and an inspection record, you have no evidence of what was done or whether the core is fit for reuse.

Planning a core cleaning, refurbishment or replacement?

Aceget supplies CPCB type-approved retrofit emission control devices for DG sets from 25 kVA to 2500 kVA. If you are weighing up whether to clean, refurbish or replace a filter core, our team can help you work out what your device needs and what documentation you should keep. Explore our retrofit emission control device range, review our certifications, or contact us with your DG set details and the core’s history.

Can a Refurbished RECD Filter Core Be Reused?