11 AERATION, VENTILATION AND AIR PURIFICATION SYSTEMS COMPRISING BLOWERS, DUCTS AND FILTERS, FOR USE IN INDUSTRIAL PLANTS; ELECTRIC FANS; WATER PURIFICATION SYSTEMS FOR SWIMMING POOLS COMPRISING PUMPS, WATER LINES AND FILTERS; AIR FILTERING UNITS FOR VENTILATION AND AIR PURIFICATION SYSTEMS IN INDUSTRIAL PLANTS; DUST FILTERING UNITS FOR THE LABORATORY; DRINKING WATER FILTERING UNITS; VENTILATION GRIDS MADE OF PLASTIC; PLASTIC BLOWERS AND PLASTIC DUST SEPARATORS FOR USE IN VENTILATION SYSTEMS; PARTS FOR PURIFICATION SYSTEMS, NAMELY PLASTIC PICKLING, RINSING AND WASHING VATS; PLASTIC STORAGE TANKS; PLASTIC MIXING VESSELS