- October 8, 2026
- Posted by: Aceget
- Category: RECD & Emission Control Devices
Walk around almost any generator installation due for an RECD retrofit and you will find a steel frame already holding the exhaust silencer. It might be a pair of legs and saddles on the floor, a wall bracket, a column-mounted cradle or a rooftop stand. It has stood there for years without trouble. The new device has to go somewhere close by, and the obvious thought follows: why not mount it on the same frame?
Sometimes that is exactly the right answer. It saves steel, floor space, anchors and installation time, and it keeps the exhaust compact. At other times it overloads an old frame, ties together two components that move differently, blocks access to both or traps the silencer in a position that no longer suits the new layout.
This article offers a structured way to decide. It sets out seven tests that a shared frame must pass, three arrangements that sites commonly end up with, and two illustrative sites where the answers differed.
What “Sharing” Can Mean
The phrase covers several quite different arrangements.
| Arrangement | Description | How much of the old frame is used |
|---|---|---|
| A. Direct reuse | The RECD is added to the existing frame with little or no change | Almost all |
| B. Extended or strengthened frame | The existing frame is extended, braced or reinforced to carry both | Most, with added members |
| C. Shared foundation, separate frames | Each item gets its own frame, but they share a plinth, base or wall | Base only |
There is also the case where the RECD replaces the silencer altogether and takes over its frame. That is a different question, covered in our article on whether an RECD can replace a generator’s exhaust silencer. Here we assume the silencer stays.
Why Owners Want to Share
The motives are sensible.
- Lower cost. A new frame, its anchors and its foundation can be a noticeable part of the installation budget. Our guide on RECD cost in India shows where project money goes.
- Less space. Generator rooms are rarely generous, and a second frame takes floor or wall area.
- Fewer penetrations. Reusing existing anchors avoids drilling a structure again.
- A compact exhaust. Keeping the silencer and device close together shortens the pipe between them.
- Faster installation. Less fabrication and fewer site welds.
Why Sharing Can Backfire
The risks are equally real.
- The frame was sized for the silencer alone, sometimes with little margin. An RECD can weigh as much as the silencer or more.
- Two hot components grow at different rates and may push against each other through a common frame.
- Vibration paths combine. A frame that carried one component quietly may resonate with two.
- Access gets crowded. Both items need service, and the RECD needs filter removal.
- The silencer’s position may not suit the device. Forcing the device into a place dictated by an old frame can add bends and backpressure.
The Seven Tests
Work through these in order. A clear failure at any step means Arrangement A is unlikely to be right. Some failures can be fixed by moving to Arrangement B or C.
Test 1: Does the frame have the capacity?
Start with the numbers.
- The silencer’s weight, ideally from the nameplate or maker’s data
- The RECD’s in-service weight, including insulation, accessories and a reasonable soot and ash load, from the vendor
- Any added pipe, flanges and fittings carried by the frame
- The weight of a technician or a removed filter module resting on the frame during service
Then ask a structural engineer to check the frame members, connections, anchors and the supporting floor or wall for the combined load. The engineer also considers how loads combine, which the structural load article describes in general terms.
Pass: the existing frame carries the combined load with an acceptable margin. Fixable: it needs added members, bracing or larger anchors (Arrangement B). Fail: the floor, wall or anchors cannot take the extra load without major work (consider Arrangement C on a different support, or a separate location).
Test 2: Is the frame in good condition?
An old frame is only as good as its weakest member.
- Look for corrosion, especially at base plates, welds and where water collects
- Check anchor bolts for rust, looseness and cracking in the surrounding concrete or masonry
- Check for bent members, cracked welds and signs of past repair
- Look for heat damage near the silencer: discoloured paint, scaling or distortion
Our guide on whether existing exhaust parts can stay discusses how retrofits work around existing components.
Pass: sound, with only surface rust that can be treated. Fixable: some members or anchors need replacing. Fail: widespread corrosion or damage; a new frame is cheaper than a repair.
Test 3: Can both items expand without fighting?
The silencer and the RECD both heat up and grow. On a shared frame, their growth must not push against each other or against the frame.
- Each item should have its own fixed saddle and sliding saddle, or an equivalent arrangement
- The fixed points should be placed so the growth of one does not push the other
- The pipe between them needs flexibility, a bend or an expansion joint, if both items are anchored close together
- The frame itself warms near hot items and grows a little; that growth should not bind the sliding saddles
Pass: the layout allows each item to move freely. Fixable: saddles can be changed or an expansion joint added. Fail: the geometry forces the items to push against each other.
Test 4: Will vibration stay under control?
The frame has carried a vibrating silencer for years. Adding a second heavy mass changes how it responds.
- Engine vibration reaching the frame depends on the engine bellows and isolation
- A stiffer, heavier assembly may shift its natural frequency closer to the engine’s running frequency, which can cause resonance
- Loose saddles or clamps can rattle and wear
Pass: the bellows isolates well, the frame is stiff and the engineer sees no resonance concern. Fixable: added bracing or isolation pads. Fail: the frame shows existing vibration problems, or analysis suggests resonance.
Our guides on how to prevent generator vibration issues and on flexible bellows in RECD exhaust systems explain the isolation side.
Test 5: Does the sequence of components make sense?
The usual arrangement places the RECD upstream of the silencer, so the device sees hotter exhaust and the silencer does its job at the end of the system. If the existing frame holds the silencer in a position that forces the RECD downstream, or forces extra bends to reach it, the shared frame may be working against the exhaust design.
- Check the flow order on the proposed drawing
- Count the bends and reducers added to fit the device onto the frame
- Ask the vendor for the total backpressure with the device and silencer in their proposed positions
Our explainer on how exhaust backpressure affects a DG set explains why the total matters.
Pass: the device sits upstream with a clean connection and acceptable backpressure. Fixable: the frame can be extended so the device sits in the right place. Fail: the frame position forces a poor flow order or excessive fittings.
Test 6: Can both be serviced?
A shared frame packs two items into one space. Both need attention.
- The RECD’s filter must come out along a clear path, often by lifting or sliding
- The silencer may need inspection, drain clearing or eventual replacement
- Flanges on both need access for bolts and gaskets
- Sensors and gauges on the RECD need to be readable
- Insulation jackets need room to be removed
Sketch the service positions on the drawing. If removing the filter means unbolting the silencer, or the silencer can only be replaced by first lifting off the RECD, the shared frame will make every service visit longer and riskier. Our RECD maintenance guide lists the tasks that need room.
Pass: each item can be serviced independently. Fixable: the frame can be lengthened or rearranged to separate service zones. Fail: the items block each other.
Test 7: Does heat and orientation work for both?
Two hot components close together raise local temperatures.
- The RECD’s insulation and the silencer’s surface both radiate heat
- Sensors and cables on the device may sit near the hot silencer shell
- Some devices are designed for horizontal mounting and others can go vertical; the shared frame must suit the device’s required orientation
Our guide on horizontal vs vertical RECD mounting explains orientation choices.
Pass: spacing and orientation suit both items. Fixable: heat shields or a revised arrangement. Fail: the device cannot be mounted in its required orientation on the frame.
The Scorecard
Record the result of each test in a table like this.
| Test | Pass | Fixable | Fail | Notes |
|---|---|---|---|---|
| 1. Capacity | ||||
| 2. Condition | ||||
| 3. Thermal movement | ||||
| 4. Vibration | ||||
| 5. Flow sequence and backpressure | ||||
| 6. Service access | ||||
| 7. Heat and orientation |
Reading the result
- All pass: Arrangement A, direct reuse, is reasonable, subject to the engineer’s sign-off.
- Some fixable, none failed: Arrangement B, an extended or strengthened frame, is usually the right path. Price the fixes against a new frame.
- Any failure in tests 1, 2, 5 or 6: usually move to Arrangement C or a separate location. These failures are expensive or impractical to overcome on the existing frame.
- Failure in tests 3, 4 or 7 only: sometimes solvable with redesign of saddles, bracing or shields; consider B before giving up.
Arrangement B in Practice: What Strengthening Looks Like
When a frame is extended or strengthened, the work usually includes some of these:
- Added legs or posts under the new device position, with their own base plates
- Diagonal bracing to stiffen the frame against sway and vibration
- Heavier cross members where the device’s saddles land
- New or larger anchors, designed for the combined load
- New saddles for the device, with one fixed and one sliding
- Isolation pads between saddles and frame members, to reduce vibration and separate dissimilar metals
- Surface preparation and repainting of the whole frame, since the old coating is often tired
Strengthening an old frame needs a drawing and an engineer’s calculation, just as a new frame would. A hurried site extension made from offcuts is a common source of later trouble, as our list of common RECD installation mistakes shows.
Arrangement C in Practice: Sharing the Base Only
When the frame itself cannot take the device, the base it stands on often can.
- A shared concrete plinth can carry two independent steel frames, each designed for its own item
- A shared wall can carry two independent brackets, if the wall passes its own checks
- A shared rooftop platform can carry separate stands, with the platform designed for both
This keeps most of the cost saving of a single location while avoiding the thermal and vibration interactions of a single frame. It also means that either item can be removed or replaced later without disturbing the other. For rooftop and basement versions, see our guides on rooftop RECD installation and RECD installation in basement DG rooms.
Two Sites, Two Answers
These are illustrative cases.
Site one: Hosiery unit in Ludhiana, 200 kVA
The setting. A 200 kVA set in a shed beside a hosiery unit. The residential silencer sat on a floor-standing steel frame about 2 m long, set on a raised plinth just outside the canopy. The frame had been painted every few years and showed only light surface rust.
The scorecard.
| Test | Result | Notes |
|---|---|---|
| 1. Capacity | Fixable | Frame members adequate for combined load after adding two legs; plinth adequate |
| 2. Condition | Pass | Light rust; anchors sound |
| 3. Thermal movement | Fixable | Silencer had two fixed saddles; one converted to sliding; device given fixed and sliding saddles |
| 4. Vibration | Pass | New bellows at engine; frame stiff |
| 5. Flow and backpressure | Pass | Device fitted upstream of silencer with one long radius bend; total within engine maker’s limit |
| 6. Service access | Fixable | Frame extended 0.9 m so the filter withdraws clear of the silencer |
| 7. Heat and orientation | Pass | Horizontal device suited the frame; a small shield protected the device’s sensor cable from the silencer shell |
The outcome. Arrangement B. The frame was extended, braced and repainted. The installation used the existing plinth and anchors with two additional anchors at the new legs. Cost was noticeably below a new frame, and the exhaust stayed compact. Textile and hosiery sites bring lint and heat concerns; our guide on RECDs for textile mills covers them. The 200 kVA DG set RECD page covers this rating.
Site two: Chemical warehouse in Vadodara, 625 kVA
The setting. A 625 kVA set in a generator room at a chemical storage warehouse. The silencer hung from a wall bracket at about 3 m height on a block wall, with a single diagonal strut.
The scorecard.
| Test | Result | Notes |
|---|---|---|
| 1. Capacity | Fail | Block wall and existing anchors unsuitable for doubling the load |
| 2. Condition | Fixable | Strut corroded at the base; repairable |
| 3. Thermal movement | Fixable | Possible with an expansion joint |
| 4. Vibration | Fail | Existing rattle already heard in the adjoining office |
| 5. Flow and backpressure | Fail | Bracket position would have put the device downstream of the silencer |
| 6. Service access | Fail | No route to withdraw the filter past the silencer at that height |
| 7. Heat and orientation | Pass | Not the deciding factor |
The outcome. Not shared. The RECD went on its own floor frame near the engine, upstream of the silencer, on the room’s concrete floor. The silencer bracket was repaired and fitted with isolation pads to cure the rattle. Warehouses with forklift traffic also need impact protection; our guide on RECDs for warehouses explains this. The 625 kVA DG set RECD page covers this rating.
Living With a Shared Frame After Installation
A shared frame that passed its tests on day one still needs watching, because it now carries two hot, vibrating items instead of one. Add these points to the routine inspection list:
| What to look at | Why it matters | How often |
|---|---|---|
| Sliding saddles on both items | A seized saddle turns thermal growth into frame stress | Every service visit |
| Bolts at new and old members | Vibration can loosen connections, especially where new steel meets old | Every service visit for the first few months, then periodically |
| Paint at welds and base plates | Corrosion starts where coatings crack | Twice a year |
| Isolation pads under saddles | Pads harden and crack with heat over time | Yearly |
| Level of each item | Sagging at one end shows a member or anchor giving way | Yearly, against the commissioning record |
| Noise in nearby rooms | A new rattle often means a loose clamp or worn pad | Whenever reported |
Record the commissioning level, bolt torques and photographs of the frame so later inspections have something to compare against. If either item is later replaced or upgraded, repeat Test 1 with the new weight before reusing the frame.
Should the Silencer Move Instead?
Sometimes the cleanest answer is to keep a single shared frame but move the silencer. If the silencer is due for replacement anyway, or its current position forces the device into a poor location, relocating it downstream onto a new or extended frame can free the best position for the RECD. Our article on noise reduction strategies for diesel generators is useful background when the silencer’s position or type is being reconsidered, and the general function of a silencer, often called a muffler, is described in the muffler article.
Before Any Steel Is Cut: Questions for the Fabricator
- What is the in-service weight of the RECD, including insulation and a loaded filter?
- Has the existing frame been checked by an engineer for the combined load? Can we see the calculation?
- Which saddles are fixed and which slide, for both the silencer and the device?
- Where is the device in the flow sequence, and what is the total backpressure?
- How will the filter be removed, and does that require moving or unbolting the silencer?
- What strengthening, if any, is proposed, and is it shown on a drawing?
- What would a separate frame cost by comparison?
The quality of the answers is a good guide when choosing CPCB approved RECD vendors, and the support decision should appear as a defined step in the RECD installation process.
Compliance Note
The device’s approval comes under CPCB’s System and Procedure for Emission Compliance Testing of RECDs. The support frame is not part of that approval, but a frame that sags, rattles or traps the filter will shorten the device’s life and complicate servicing. Keep the scorecard, drawings and engineer’s check with your installation records. If the silencer’s arrangement changes, confirm that noise limits are still met.
Frequently Asked Questions
Can an RECD be mounted on the same frame as the silencer?
Yes, if the frame has the capacity, is in good condition, lets both items expand, controls vibration, keeps a sensible flow order, allows independent service and suits the device’s orientation. Often the frame needs strengthening first.
Is sharing a frame always cheaper?
Usually it costs less than a completely new frame, especially when only modest strengthening is needed. If extensive repair is required, a new frame can work out cheaper and better.
Should the RECD go before or after the silencer?
Usually before, so the device sees hotter exhaust and the silencer finishes the job. Follow the vendor’s recommendation for your system.
What if the silencer frame is on a wall?
Check the wall’s capacity carefully. Block walls and partitions rarely suit doubling the load. A separate floor frame for the device is often safer.
Do the silencer and RECD need separate saddles?
Yes. Each needs its own fixed and sliding arrangement so their thermal growth does not push against each other.
Can the shared frame cause vibration problems?
It can, if the added mass brings the frame close to resonance or if saddles are loose. A good engine bellows, a stiff frame and isolation pads reduce the risk.
Share Only What Passes the Tests
A shared frame is not a shortcut or a mistake in itself. It is a design choice that works when the old steel can carry the new load, when both hot items can move freely, when vibration stays controlled, when the flow order makes sense and when technicians can reach each item without dismantling the other. Run the seven tests, score them honestly and choose between direct reuse, a strengthened frame or a shared base. The result will be cheaper than doing everything new and far more reliable than bolting the device onto whatever steel happens to be there.
Aceget assesses existing silencer frames during RECD site surveys and designs strengthened or separate supports as the tests require. To have your silencer frame reviewed, talk to Aceget, or explore the retrofit emission control device range.