How to overhaul an auxiliary fan for underground mining

Why auxiliary fans matter in underground mining

Primary ventilation systems move large air volumes across the mine. Auxiliary fans do the precision work.

They are typically used to:

• Push fresh air into development headings, stopes and dead ends
• Extract contaminated air from areas where diesel equipment, blasting fumes or dust build up
• Support temporary or changing work areas where permanent ventilation is not practical

Their portability is part of the appeal. Auxiliary fans are compact, can be relocated as mining progresses and are used with flexible ducting so air goes exactly where it is needed.

Because they often operate in harsh conditions, auxiliary fans are exposed to dust, vibration and frequent handling. Downtime or non-compliance can quickly become a safety, production and regulatory problem, which is why a structured overhaul process is so important.

When to plan an auxiliary fan overhaul

Overhauls are usually driven by a combination of:

• Statutory requirements for flameproof and explosion protected equipment
• OEM recommendations on operating hours and service intervals
• Condition based triggers such as increased vibration, noise, poor performance or repeated defects

Planning ahead is critical. Having clear visibility of upcoming overhaul dates, along with pre-overhaul inspections, allows mines to:

• Book workshop capacity
• Organise temporary ventilation or spare units
• Align the overhaul with other planned shutdown activities

This aligns well with broader asset management and mechanical overhaul strategies that look at the full equipment lifecycle, not just individual failures.

Step by step: a typical auxiliary fan overhaul process

Although each site and fan type will vary, a good overhaul process usually follows similar stages.

1. Strip and assess

After safe isolation and transport to the workshop, the fan is stripped down so that all critical components can be inspected. This often includes:

• Motor and windings
• Impeller, shaft and keyways
• Bearings, seals and housings
• Flameproof enclosures and terminal compartments where applicable

The goal is to build an honest picture of the condition, separating minor wear from issues that affect safety or reliability. A clear strip and assess report provide the mine a basis for approving the scope before major work proceeds.

2. Aligning with AS/NZS 3800 and AS/NZS 5368

For flameproof auxiliary fans, the overhaul must preserve explosion protection properties. That is where standards such as AS/NZS 3800 and AS/NZS 4871 (now AS/NZS 5368) come in.

Key activities at this stage include:

• Checking flamepaths for damage, corrosion or wear beyond allowable limits
• Verifying that certified fasteners and glands are correct, undamaged and properly engaged
• Inspecting internal components for tracking, arcing or overheating
• Confirming ingress protection, cable terminations and earthing arrangements

Any proposed repairs or modifications should be reviewed by suitably qualified people so that compliance is maintained throughout the work, not just at the end.

3. Mechanical refurbishment

On the mechanical side, auxiliary fan overhauls commonly involve:

• Rewinding or replacing the motor if insulation resistance or test results indicate deterioration
• Restoring impeller balance and addressing any shaft run out
• Replacing bearings and seals, paying attention to correct fits and lubrication
• Repairing or replacing guards, frames and mounting hardware

Good workshops will combine machining, balancing and other mechanical overhaul activities so that the rebuilt fan runs smoothly and within specified vibration levels.

4. Electrical and functional checks

Electrical work is more than just replacing like for like components. Typical checks include:

• Insulation resistance testing
• Verification of protection settings and safety devices
• Functional testing of controls, starters and monitoring equipment where they are part of the package

For flameproof equipment, all electrical work is carried out within the control of the certified system so that the explosion protection concept is preserved.

5. Final testing, documentation and certification

Before the fan leaves the workshop, it should be tested as a complete unit. This often involves:

• Running tests to confirm current draw, vibration, noise and airflow performance
• Verification of rotational direction and controls
• Pressure testing and inspection of flameproof joints where required

All measurements and test results are documented, along with details of repairs and replacements. This documentation supports certification under AS/NZS 3800 and forms part of the equipment history for future inspections and audits.

Practical lessons for mines

Looking across auxiliary fan overhauls, a few themes tend to repeat:

• Early planning reduces risk. Knowing overhaul dates and condition ahead of time prevents last minute ventilation gaps.
• Compliance and performance go together. Treating AS/NZS 3800 and AS/NZS 5368 as design tools, not just paperwork, results in safer and more reliable equipment.
• Integrated capability saves time. Workshops that combine mechanical, electrical and flameproof expertise can turn around fans faster while maintaining control over quality.
• Documentation matters. Clear records make future inspections easier and provide evidence that equipment is fit for service.

Viewing auxiliary fans as critical safety assets, rather than ancillary gear, helps set the right expectations for overhaul quality and timing.

How we support auxiliary fan overhauls

Ampcontrol provides overhaul and repair services for auxiliary fans and other underground ventilation equipment through our AS/NZS 3800 certified workshops in New South Wales and Queensland. We combine:

• Integrated mechanical and electrical overhaul capability
• Experience with flameproof and explosion protected equipment
• Site-based service and maintenance teams who work alongside our workshop technicians

If you are reviewing your auxiliary fan overhaul strategy or want to benchmark your current process, reach out to our team or submit an enquiry.