All-Flo, the manufacturer of air-operated diaphragm (AOD) pumps, was challenged to construct an entire pump with conductive albeit non-metallic materials for a mining application. All-Flo turned to custom plastics compounder RTP Co., in Winona, Minn., which came up with a material that enabled the successful production of a specialized version of the pump maker’s 1-inch (25-mm) polypropylene AOD pump.
All-Flo has long used non-metallic materials for its pumps. Traditional fluid handling pump designs favored metals, but many end-users demand non-metallic materials that either resist corrosion from harsh chemicals or reduce weight for portability. “Plastic materials provide benefits that we simply could not otherwise obtain,” said Paul McGarry, All-Flo’s sales and marketing manager.
“Miners have to carry equipment down in tight elevators or often walk it from hole to hole,” McGarry said, referring to their weight benefits. “Using RTP’s glass-fiber-reinforced polypropylene compounds enables us to achieve the considerable weight savings, while providing a stronger degree of resistance to atmospheric corrosion.
“While many of All-Flo’s pumps can meet ATEX Directive requirements for being safe to operate in potentially explosive environments, safety standards can vary from country to country and some companies have their own safety standards that are stricter than regulations require,” McGarry explained, referring to the recent customer challenge to construct the AOD pump using conductive, non-metallic materials.
Working in partnership with All-Flo and the pump maker’s injection molder, Royal Plastics, in Mentor, Ohio, RTP evaluated and trialed a number of materials, each with a different glass-fiber loading, in search of the necessary mechanical properties required for the pump. A variation of RTP’s 100 Series glass-fiber-reinforced polypropylene compound that All-Flo already used was chosen after passing evaluation testing.
The addition of a carbon powder provided the conductive properties to meet application requirements that satisfied the European ATEX Directive standards for use in hazardous environments (preventing static discharge that could be aggravated by fumes or dust to cause an explosion). The ESD C 100 Series compound that RTP employed has a surface resistivity of less than 10-6 ohm/sq and is considered electrically conductive.
“Not only did RTP provide a conductive material that had the properties and met the requirements, it had the same processability and worked with our existing molds,” said McGarry. “For our molder, Royal Plastics, it’s really just a matter of switching out materials to produce a specialized version of our polypropylene pump.”
Some All-Flo pumps incorporate plastic compounds based on acetal resin. Acetal is a thermoplastic material commonly used in pumps due to its inherent wear resistant characteristics for certain media conveyed.