Manufacturers. We are a worldwide operating and leading manufacturer of filters â€“ certified under ISO 9001/14001 and approved by more than 80 classification societies. We are specialist for the filtration of liquids and gases. Our automatic, duplex and simplex filters are the result of our own research and development and comply with international technical standards. BOLLFILTERs protect important parts such as valves, pumps and bearings from contamination and accumulation of mud. They are installed into the pressure line or suction line. Depending on type and application, the filter housings are made of grey cast iron, nodular grey cast iron, carbon steel or CrNi-steel. They are designed in accordance with national and international regulations and standards. Continuous or intermittent operation, manual or fully automatic cleaning of the filter elements will determine the choice of filter type.