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SS Duct Wall Exhaust — FG3G630 Case Study

IP65 Stainless Steel Duct Wall Exhaust
FG3G630 Large-Diameter EC Tube Axial Fan

ClientEuropean Ventilation System Integrator

ApplicationSS Duct Wall Exhaust System

ModelFG3G630-4AGL-3A

Fan Type630mm EC Tube Axial with Guard

Ingress ProtectionIP65 Custom Sealed (Standard IP56)

Duct & Bracket304 SS · 1.2mm Wall · Cross-Adjustable

Operating DutyContinuous 24/7 · −20°C to +55°C

Lead TimeSample 7 days / Production 14−21 days

1. Project Background & Requirements

A European ventilation system integrator with over 15 years of industrial air handling experience took on a retrofit project for a food additive plant in Eastern Europe. The existing system also used a 630mm axial fan — airflow and static pressure were adequate on paper. But after less than a year of operation, the fan was failing repeatedly. A teardown inspection revealed two root causes:

Plastic bracket joints loosened under vibration — the original bracket's adjustment joints used nylon PA6 plastic heads. Under continuous duct vibration, the plastic friction surfaces gradually wore down, losing approximately 30% of clamping force per quarter. Within six months, the joint gap exceeded 0.5mm, causing the fan to shift off its mounting axis and the impeller to scrape against the duct wall.
Bracket body rusted through — the bracket was made of galvanized steel. In an environment of alternating condensation and chlorine-based cleaning solutions (sodium hypochlorite is standard in food plant sanitation), the zinc layer dissolved rapidly. Within six months, widespread red rust appeared — weakening structural strength by ~40%, shedding rust particles into the food-grade exhaust airstream, and creating galvanic corrosion at the stainless steel duct interface.

The client's three critical requirements:

IP65 ingress protection — the fan is embedded in the duct wall with direct outdoor exposure. Condensation, rainwater backflow, and daily high-pressure hose washing demand full dust-tight sealing. The EC control board must be potted (encapsulated) to achieve true IP65.
Full 304 stainless steel bracket + fasteners — eliminate rust at the root. Every bracket component, including adjustment joints, must be 304 SS. No plastic, no galvanized steel.
Field-adjustable mounting with metal-on-metal locking — the duct wall cutout cannot be cut with precision on site. The bracket must allow fine adjustment, and the locking mechanism must not loosen under vibration — ever.

2. Old Fan Failure Analysis: It Wasn't the Diameter

The previous fan was also a 630mm axial — airflow and static pressure were adequate on the datasheet. Yet it failed repeatedly within a year. The teardown told the real story:

2.1 Plastic Adjustment Joints — Chronic Failure Under Vibration

The old bracket's adjustment joints used nylon PA6 plastic heads, clamped by a bolt to lock the angle. The design intent was light weight and low cost, but under continuous duct vibration (measured 2.8–4.5 mm/s), the plastic friction surfaces experienced progressive wear. Clamping force degraded by approximately 30% per quarter. Within six months, the joint gap exceeded 0.5mm, shifting the fan off its mounting axis. The impeller began scraping the duct wall — producing harsh noise and damaging blades.

Root cause: Plastics creep and wear under sustained micro-vibration. This is an inherent material property — no amount of "tightening it more" can fix it. The adjustment mechanism must be all-metal.

2.2 Galvanized Steel Bracket — Rust Was Inevitable

In a duct wall exhaust installation, the bracket lives in a cycle of condensation and chlorine-based cleaning solutions (sodium hypochlorite is standard for food plant sanitation). The old bracket used galvanized steel. The zinc layer dissolved rapidly in the presence of chlorinated cleaners. Within six months, widespread red rust appeared:

Structural strength reduced by approximately 40% due to section loss
Rust particles shed into the airstream — unacceptable in a food-grade exhaust environment
Electrode potential difference (~0.3V) between the zinc layer and the 304 SS duct accelerated galvanic corrosion at every contact point

Conclusion: The fan itself was never the problem — same diameter, same airflow. The failures were 100% in the bracket material and joint design. All-304-SS construction with metal-on-metal locking joints is the only viable solution.

3. Solution Design

3.1 Model Number Decoding & Specifications

Parameter	Value	Notes
Model	FG3G630-4AGL-3A	Large-diameter EC tube axial with guard
Impeller	630 mm	Axial impeller
Motor	EC brushless DC	Nominal ~1150 rpm · efficiency ≥ 90%
Rated Power	0.8 kW	EC high-efficiency · low power draw
Max. Airflow	14,500 m³/h	Free air, zero back pressure
Max. Static Pressure	240 Pa	Zero-flow shutoff pressure
Sound Level	69 dB(A)	Full speed
Standard IP Rating	IP44	Dust-protected + Powerful water jets
Custom IP Rating	IP65	Fully dust-tight + Water jets · potted terminal box
Speed Control	0–10V / PWM / Modbus RTU	0–10V selected · plant DCS integration
Certifications	CE / ISO 9001 / ErP 2026	—
Weight	~15 kg	Including motor + housing + guard

3.2 Critical Customization: EC Control Board Potting for IP65

EC fans differ fundamentally from traditional AC fans — they have no separate motor junction box. The EC control board (rectifier + VFD drive + 0–10V/PWM signal interface) is integrated and enclosed within the motor's terminal cover. The FG3G Series ships standard at IP56 — suitable for most outdoor duct installations. For this project, the upgrade to IP65 was achieved through control board potting and targeted sealing improvements:

Full control board potting with silicone rubber — the terminal cover is opened, and the entire EC control board — including all connectors, capacitors, and MOSFETs — is encapsulated in silicone rubber. Once cured, it forms a seamless 3–5mm protective layer. Even if the terminal cover gasket ages and moisture penetrates the cover, the control board itself is completely isolated from water. This is the core IP65 guarantee.
Terminal cover gasket upgraded to FKM (Viton) — the original NBR gasket swells and degrades under chlorine-based cleaners. FKM offers over 5× the chemical resistance in this environment.
Double-lip stainless steel skeleton oil seal on the shaft — prevents water jet ingress along the motor shaft. The dual-lip design creates two independent barriers, with high-temperature grease packed between the lips.

Potting is the standard process for achieving IP65 on EC fans — it adds no external dimensions, no additional enclosures, and approximately 8–12% to unit cost. For a continuous-production exhaust line, this premium eliminates the risk of a water-damaged control board entirely.

3.3 Mounting System: All-304-SS Cross-Adjustable Bracket

Addressing both failure modes of the old bracket — plastic joint loosening and galvanized steel rust — the replacement bracket was redesigned with every component in 304 stainless steel, every adjustment joint metal-on-metal.

Elliptical slots + metal-on-metal locking joints — ±15mm field adjustment. In place of the old plastic clamp heads, stainless steel lock nuts provide sustained clamping force through elastic deformation of the metal. Unlike plastic, metal does not creep or wear under micro-vibration.
Triangular base plates — distribute 78 kg across 6× M10 stainless steel bolts. Each bolt carries ~13 kg — safety factor > 8.
All-304-SS construction — bracket body, flange plate, and every bolt/nut/washer are 304 stainless steel. Zero rust risk, zero galvanic corrosion at the SS duct interface. This directly eliminates both failure modes of the old galvanized bracket.

5mm EPDM isolation pads — placed between bracket and flange. Decouple motor vibration from the duct wall while protecting the flange contact surface from fretting wear.

3.4 Variable-Speed Control via DCS

Operating Mode	Airflow Demand	0–10V Signal	Speed	Power Draw
Standby ventilation	2,000 m³/h	2.0V	~400 rpm	0.15 kW
Normal production	6,000 m³/h	5.5V	~800 rpm	0.4 kW
Peak exhaust	10,000 m³/h	9.0V	~1,100 rpm	0.7 kW

The EC motor's part-load efficiency is the standout advantage. Standby power draw is ~0.15 kW — over 60% lower than an equivalent AC motor — saving over 3,000 kWh/year.

4. Installation & Commissioning

Duct wall cutout — plasma-cut 620×620mm square opening. Deburr edges to R3 radius.
Flange seating — 3mm EPDM gasket. Cross-torque M10 bolts to 40 N·m.
Bracket alignment — hang the cross bracket on inner flange face. Use elliptical slots for ±15mm fine positioning.
Fan placement — hoist FG3G630 into position. Engage 4× M12 eyebolts, align, and lock down.
Electrical termination — route 0–10V control + power through IP65 cable gland. Pot terminal box with silicone.
Commissioning — ramp speed in steps. Record current, airflow, vibration. Cross-check against factory PQ curve.

Three field essentials: ① Verify G½" drain plug faces downward — schedule periodic condensate draining. ② Maintain ≥ 400mm clearance on inlet side for impeller access. ③ Verify earth continuity: SS duct → flange → bracket → fan housing ≤ 0.1Ω.

5. Measured Performance

Parameter	Design Target	Measured	Deviation
Airflow at 200 Pa back pressure	8,500 m³/h	8,380 m³/h	−1.4%
Max. Static Pressure	240 Pa	235 Pa	−2.1%
Sound Level at 3m (full speed)	≤ 69 dB(A)	67.5 dB(A)	✅ Better than rated
Motor Efficiency	≥ 90%	91.3%	✅
Vibration Velocity	≤ 3.5 mm/s	2.8 mm/s	✅
IP65 Seal Integrity	No water ingress	No water ingress	✅ Passed pressure-wash test

6. Engineering Takeaways

6.1 Bracket Material Is the #1 Criterion for Duct Wall Exhaust

The old fan was also 630mm — the fan itself was never the problem. Duct wall exhaust installations subject the mounting system to a triple threat: condensation, chlorine-based cleaners, and continuous vibration. Plastic joints will loosen. Galvanized steel will rust. When selecting a fan for this application, impeller diameter and airflow are just the starting point — bracket material and joint design determine system lifetime. All-304-SS construction + all-metal locking joints + EPDM isolation pads: all three are non-negotiable.

6.2 IP Rating Selection Guide

Installation Location	Standard IP	Recommendation
Indoor, dry duct	IP44	Basic dust protection
Indoor, condensing duct	IP54	Splash-proof
Outdoor, with weather hood	IP55	Low-pressure water jets
Duct wall embedded · direct outdoor exposure	IP56 standard · IP65 custom	Powerful water jets + fully dust-tight
Fully exposed, no weather protection	IP66	Heavy seas / powerful water jets

The FG3G Series' standard IP56 rating already covers most duct-wall-embedded scenarios. This project's IP65 upgrade was driven by daily pressure-washing. The ~8–12% cost premium is easily justified against the downtime cost of a water-damaged motor on a continuous-production exhaust line.

6.3 Material Compatibility

304 SS duct + non-SS brackets = galvanic corrosion within 6–12 months in condensing environments (electrode potential difference > 0.3V). Specify uniform 304 SS for all fasteners, brackets, and flange plates.

7. Additional Applications (FG3G Series)

Food processing exhaust — 304 SS + IP56/IP65 meets HACCP hygiene requirements
Chemical lab fume hood exhaust — corrosion-resistant + ATEX Zone 2/22 available
Underground parking CO exhaust — high flow + low noise for long duct runs
Wastewater treatment odour extraction — IP56 + SS resists H₂S corrosion
Marine machinery space ventilation — compact + salt-spray resistant