Fan and motor drive refurbishment on closed-circuit evaporative coolers

Equipment

A closed-circuit evaporative cooler passes process fluid through a coil that is wetted by spray water and cooled by air drawn through the unit by a fan. The fan is driven by a motor through a V-belt drive: motor pulley and bush, fan pulley and bush, belts, and the fan shaft on its bearings.

Failure modes

Pulley grooves wear and belts ride low, slip and overheat; taper-lock bushes loosen and fret on the shaft; belts crack and fail; fan-shaft bearings corrode and seize; casings and drift eliminators corrode; spray nozzles block and the coil scales.

Common causes

The wet environment and water carry-over onto the drive; belt tension outside specification; misaligned pulleys; lubrication intervals missed on bearings in a hard-to-reach location; and pulleys left in service after the groove profile has gone.

Inspection

Check belt tension and condition; inspect pulley grooves with a gauge; look for rust bleed at bushes; check bearing temperature and vibration; inspect the coil for scaling and the eliminators and casing for corrosion; confirm water treatment and bleed-off are working.

Maintenance

Tension and align belts to the manufacturer’s figures; replace belts as a matched set; grease fan-shaft bearings to schedule; keep spray nozzles clear and water chemistry in range; touch up coating damage on the casing before it spreads.

Repair and refurbishment

A drive refurbishment replaces the fan pulley and bush, motor pulley and bush, and belts, checks the fan shaft and bearings, and re-aligns the drive. The unit returns to service with the drive train restored to specification; where the coil or casing is also deteriorated, the scope extends to coil cleaning or replacement and casing repair.

Replacement

Replace the cooler when the coil has failed and is uneconomic to replace, or when the casing has corroded beyond repair. Drive-train refurbishment is normally a fraction of that cost.

Umbusso capability

Umbusso refurbished three EVAPCO closed-circuit evaporative coolers at an Eskom power station in 2024 — new fan pulleys and bushes, motor pulleys and bushes, and restored V-belt drive trains under an Eskom order.

This article is general technical guidance. Intervals, standards and methods must be confirmed against the current regulation, the manufacturer’s documentation and the site standard before they are applied.