When the installation forces a large-diameter fan to turn slowly — because space, rotor inertia or noise is the constraint — most families either over-speed or won't fit. The Large-Backward family runs a single big backward-curved wheel at low speed, holding the non-overloading character of a backward fan while still reaching high static at modest flow. It is a specialised large-format pick, not a general workhorse: we build it when size and speed are the constraint, and we tell you when a smaller family is the better answer.
The Large-Backward wheel is a single large backward-curved impeller built for diameter rather than speed. Pressure on a centrifugal fan comes from tip speed, and tip speed is diameter × RPM — so a big wheel makes its pressure at a lower RPM. That trade is the whole point of the family: it lets you hold high static where the installation will not let the fan spin fast.
A large-diameter rotor that develops its pressure at low RPM — for installations where speed, rotor inertia, height or footprint is the binding constraint, not airflow volume.
High static at modest flow — proven on this wheel to 1,700 mmWC (software ceiling ~1,756 mmWC) on a single backward-curved impeller, not a multi-stage build.
Backward-curved, so the power curve is non-overloading — power peaks then falls, the motor is protected off-design, and the low tip speed keeps it quieter at size.
A normal backward fan is more efficient and cheaper. The Large-Backward family earns its place only when one of these three drivers is binding. Pick it for the right reason and it solves a problem a smaller wheel cannot; pick it when size is not the constraint and you simply pay for diameter you did not need.
A constrained installation caps rotational speed — noise limits, rotor inertia, drive or foundation limits, or a long slow-start requirement. A normal-diameter wheel cannot make the pressure at that RPM.
How we engineer it outA larger diameter develops the required tip speed at lower RPM. The wheel is sized to make its static at the speed the installation allows, not the speed the duty would prefer.
Modest flow but high static — to ~1,700 mmWC — is awkward for the efficient mid-size backward families and overkill for a multi-stage build.
How we engineer it outThe large backward-curved wheel reaches the static on one impeller at 140 m/s tip, keeping the non-overloading characteristic and a single, serviceable rotor.
Optimising a wheel for large diameter and low speed costs aerodynamic efficiency — peak static efficiency sits below the smaller backward families, by design.
How we engineer it outWe size the drive honestly to the absorbed power and tell you when size is not your real constraint — in which case a smaller, more efficient backward family is the right and cheaper pick.
This is not a catalogue near-fit. The fan is engineered to your flow, static, temperature and the installation constraint that made it a large-format job in the first place.
No catalogue fan forced onto your spec. The large wheel is sized so your duty point sits in the stable region of its curve at the constrained RPM — then the unit is verified on the 200 HP VFD test rig and dynamically balanced before dispatch.
| Parameter | Standard | On application |
|---|---|---|
| Volume flow | up to ~50,600 CMH | narrowest-flow family — high flow → step to the Backward-Flat Plate family |
| Static pressure | up to ~1,750 mmWC | higher on enquiry within the 2,000 mmWC envelope |
| Continuous gas temperature | up to 600 °C with HT construction | standard HT build to 300 °C; above 150 °C a shaft cooling disc is fitted |
| Dust tolerance | Clean duty — light dust only | dusty / abrasive gas → the Radial-Tip family (high dust) or the Radial family (the heaviest dust in our range) |
| Peak static efficiency (character) | Size / low-speed optimised, below the smaller backward families by design (exact figures shared on enquiry) | efficiency-led clean air → the Aerofoil family / the Backward-Curved Plate family |
| Drive power | up to 335 HP (214 kW absorbed at maximum) | verified on our proprietary fan-selection software, within the 400 HP envelope |
| Balance quality | ISO 21940 G6.3 | G2.5 / G1.0 on application — important on a large rotor |
| Bearing life (design target) | L10h ≥ 40,000 h continuous | longer L10 on application |
The Large-Backward family has the narrowest flow envelope in the range — a single wheel built large and slow. It is a specialised large-format / high-static pick, not a high-volume workhorse: if airflow volume is the driver, the high-flow Backward-Flat Plate family is the right answer, and if size is not your real constraint a smaller backward family is more efficient and cheaper. This is a clean-duty family — clean or lightly dust-laden gas only.
The same engineering language carries from your enquiry to the GA drawing to the nameplate — expressed in the standard AMCA conventions, with the descriptive family name and generic blade type, never an internal model code.
| Specification field | Options |
|---|---|
| Arrangement (AMCA 99) | Arr. 1 (overhung, fan bearings) / Arr. 8 (overhung on common base) / Arr. 9 (overhung, motor side) / Arr. 10 (overhung, motor inside base) — selected by drive, access, large-rotor support and temperature. |
| Width / inlet | SWSI (single width, single inlet) — the standard build for the Large-Backward family. For high flow at moderate pressure on a double-width wheel, step to the Backward-Flat Plate family rather than forcing DWDI here. |
| Wheel type | Large backward-curved (low-speed) — a single large impeller optimised for diameter and speed constraint rather than peak efficiency; non-overloading power characteristic. |
| Class (by pressure / outlet velocity) | Class selected from the duty point on the pressure-vs-outlet-velocity limits; the wheel runs a 140 m/s structural tip speed and is sized to make its static at the constrained RPM. |
| Materials of construction | MS (standard) / SS304 / SS316 (full or airstream) for clean corrosive duty / Corten or duplex per duty / FRP (F suffix). Wear-plating is not a Large-Backward feature — it is a clean-duty family. |
| Construction suffix | HT (high-temperature: refractory / high-temp metallurgy + shaft cooling disc above ~150 °C) / SR (spark-resistant, ATEX Category 3 where the area requires) / F (FRP airstream) — appended to the family designation per duty. |
| Drive | Direct-coupled / V-belt / VFD with shaft-earthing ring (suits the low-speed, noise-constrained brief). Motor to 335 HP (214 kW absorbed at envelope maximum), verified on our proprietary fan-selection software rather than estimated. |
| Large-rotor scope & accessories | Split / sectioned casing and a rotor-handling SOP (crane + large machining) where size demands; split SNL plummer-block bearings for maintainability; inlet box and dampers; in-cone IGV; flexible connectors and AV mounts; silencers; shaft cooling disc above 150 °C; witnessed FAT and G2.5 balance on the large rotor. |
Every job's performance is verified at our works on the 200 HP VFD test rig, to the AMCA 210 / ISO 5801 method, before dispatch.
Large-format clean-side draught and conveying air on space- or speed-constrained installations.
High-static process-air and conveying duty where a large, slow rotor suits the plant footprint.
Clean high-pressure process air; SS / Corten airstream for corrosive clean duty.
Dilute-phase pneumatic conveying of flour and granular product on large, quiet wheels.
Hot clean process air with HT construction and a shaft cooling disc above 150 °C.
Large clean-duty AHU and process-air builds where noise and inertia constrain the wheel.
Clean-side high-static draught packaged into APC trains on a constrained large-format fan.
7 centrifugal fan families across the range. Tell us your constraint.
What our marks mean, in the words that survive an audit.
Tested to the AMCA 210 / ISO 5801 method, in-house on our 200 HP VFD rig. Tested-to-method — not AMCA-certified.
ISO 9001:2015 — third-party certified. Our only third-party certification.
Self-declared per 2006/42/EC + 2014/35/EU (Module A). A self-declaration, not a notified-body certificate.
Self-declared, Zone 2/22, Category 3, per 2014/34/EU, where the area classification calls for it.
Designed and built to API 673 as project-specific scope.
ASME Sec IX qualified welders + WPS for every joint.
ISO 21940 — G6.3 minimum, G2.5 / G1.0 on application.
ISO 20816 evaluation; ISO 14694 for fan-specific limits.
| Stage | Standard duty | API-673 / engineered |
|---|---|---|
| Offer / quotation | 3 working days — always | 7–10 working days |
| GA drawing for approval | 2–3 weeks from PO | 3–4 weeks from PO |
| Manufacture + balance + paint | 6–10 weeks | 10–14 weeks |
| Performance test + witnessed FAT | ~1 week | 1–2 weeks |
| Order-to-dispatch (total) | 9–14 weeks | 14–20 weeks |
Shutdown-driven replacements: we have shipped fans within 6 weeks of a clean PO. Tell us your shutdown window and we commit to a dated plan.
The same engineering, viewed three ways — by fan family, by duty, and by industry. Follow the cross-references.
No model numbers needed. Give us the operating conditions — flow, static, gas temperature, composition, particulate, and any tender standard — and our application engineers size the fan and quote it. Attach a spec or GA if you have one.
+91 90110 09155 · mihir.jitamitra@gmail.com