Flexible connectors prevent fan vibration reaching the ductwork; correct material and installation decide whether they work.
Purpose and Materials
A flexible connector is a short, compliant section between the fan flange and the duct that absorbs vibration and slight misalignment so the rigid duct does not become a vibration bridge carrying noise into the wider building structure.
A flexible connector is a short, compliant bridge, and its whole value is in being a break in the vibration path; treat it as a structural member and it stops working. The material and the fit decide whether it isolates or merely connects.
Temperature and exposure set the material: canvas or reinforced fabric for moderate, dry ventilation; neoprene or elastomer where moisture or mild chemical is present; metal bellows where the airstream is hot or pressurised beyond what fabric survives. Picking by convenience rather than condition is the usual cause of early failure at the joint.
Fit is the second half: the connector must hang or sit neutral, with no pull on either flange, because tension or compression preloads it and turns the compliant section into a stiff link that transmits force. Length is kept just enough to flex, since a slack loop sags into the airstream, adds resistance, and can be drawn into the wheel.
The fire rating at a penetrated wall is easy to forget and costly when missed; the connector material must match the wall's rating at that penetration or the compartment line the wall provides is broken at the fan. The joint is sealed and inspected at commissioning rather than assumed correct, because a small leak loses pressure and whistles.
The company's 80,000 m² production site builds ventilation equipment under ISO 9001:2015 with CCC certification, and its engineers respond to selection enquiries within 24 hours to specify connector material and length against the airstream temperature and any fire-rated penetration the layout includes.
The connector is a wear item, not a fit-and-forget part: fabric ages under heat, oil, and UV at an external intake, and a cracked section bridges vibration and leaks, so it is on the inspection round with a defined replacement interval. A spare of the correct length and material is kept so a failed connector is swapped in a shut-down rather than patched, and the replacement repeats the neutral fit and the sealed flange so the new joint isolates as well as the first.
Fabric or reinforced canvas connectors suit general ventilation where temperature is moderate and there is no fire or grease concern, and they are light and easy to fit with standard clamping and a simple flange arrangement.
Neoprene or elastomer connectors resist moisture and mild chemicals, while metal-bellows types handle high temperature or pressure where fabric would fail, and the choice follows the actual airstream condition rather than convenience.
The connector must be airtight at the flange, because a leaking joint loses static pressure and can whistle, undermining both performance and the acoustic benefit the flexible section was meant to provide at the fan connection.
Installation Mistakes
The most common fault is fitting the connector under tension or compression, which preloads it and transmits force instead of isolating; it should hang or sit neutral, with no pull on either flange, so the fabric or elastomer stays relaxed in service.
Sagging fabric that balloons into the airstream adds resistance and can be sucked into the fan; the connector length should be just enough to flex, not a long slack loop that invites both flow loss and a dangerous entanglement with the wheel.
Missing the fire or smoke rating where the duct passes a rated wall defeats compartmentation; the connector material must match the wall rating at that penetration, or the fire separation the wall provides is quietly lost at the fan connection.
Bolting through both flanges with the fabric trapped but not torn, and sealing the edge, is the detail that keeps the joint quiet and leak-free over years, and it should be inspected at commissioning rather than assumed correct.
| Item | Specification | Note |
|---|---|---|
| Material | canvas / neoprene | By temperature |
| Length | short | No slack loop |
| Fit | neutral | No tension |
| Seal | airtight | No leak loss |
| Rating | match wall | Fire rating |
| High temp | metal bellows | Where fabric fails |
Selection Checklist
- Choose material for the temperature and any fire rating.
- Fit the connector neutral, never stretched or compressed.
- Keep the length short to avoid sag into the airstream.
- Seal the flange edge for an airtight, quiet joint.
- Match the penetration fire rating where required.
- Use metal bellows for high-temperature duties.
About the Manufacturer
Keruite Air Conditioning Group, headquartered in Dezhou, Shandong, has more than 30 years of HVAC manufacturing experience and operates an 80,000 m² production site with its own performance testing laboratory. Products are built under ISO 9001:2015 quality management and carry CCC certification, and are supplied to customers in over 50 countries.
Our engineers respond to selection enquiries within 24 hours and can provide project-specific sizing, performance curves, and documentation to support specification and procurement.