Solid-Body AODD Pumps Ideal for Transfer of Hazardous Chemicals

Contributed by: Sergio Avila at Almatec

In first century A.D., sulfuric acid was referred to as “vitriol” by Greek physician Dioscorides and Roman naturalist Pliny the Elder. Today, this highly corrosive mineral acid is one of many dangerous chemicals used in manufacturing processes around the world, such as automotive applications, fertilizer manufacturing, oil refining, and wastewater processing. Designated as ‘highly hazardous’ (toxic and reactive with high potential for human injury), the safe containment, handling, and transfer of sulfuric acid –and chemicals like it– is critical.

Strict regulations, certifications, and labeling requirements ensure that manufacturers meet safe distribution and transfer standards within the global chemical manufacturing process to protect the people working with these hazardous materials and the environment. The dangerous nature of these chemicals means that they also require highly specialized pumping equipment for their safe transfer. While not all hazardous chemicals can be handled by the same pumping equipment, there are important factors to consider when choosing between different pumps.

Chemicals have unique properties that make them more or less volatile in certain environments. These considerations are important for correct pump specification given the application. In 2007, this point was solidified by an explosion at a Barton Solvents facility in Wichita, Kan. The facility was transferring Naphtha, a flammable liquid that can produce ignitable vapor-air mixtures inside tanks. Due to its low electrical conductivity, the vapors accumulated dangerous levels of static electricity and ignited, causing an explosion that destroyed the tank farm, injured 11 residents, and forced the town’s 6,000 residents to evacuate. Following this incident, the U.S. Chemical Safety and Hazard Investigation Board ruled that non-conductive flammable liquids capable of forming ignitable vapor-air mixtures should be pumped at reduced velocities to minimize risk of static ignition.

Pumps remain the most critical component in the safe transfer of hazardous chemicals, although the correct pipes, valves, seals, and connectors are important as well. Consider these important factors when choosing a pump to handle dangerous chemicals:

  • Leak-free
  • Dry run capabilities
  • Self-priming
  • Chemical-compatible materials of construction
  • Shear sensitive
  • Deadheading
  • Ease of maintenance

Air-operated double-diaphragm (AODD) pumps meet all these requirements. AODD pumps are reciprocating, positive-displacement type pumps powered by compressed air rather than electric motors, which allows them to run dry and deadhead without damage. The pumps do not require mechanical seals, either, making them virtually leak-proof. AODD pumps also provide strong suction and are shear-sensitive.

Other pump types, such as lobe pumps and gear pumps, have many of the same characteristics as AODD pumps but are less ideal for dangerous chemical transfer. Lobe pumps, for example, are prone to slipping, resulting in inconsistent flow rates and production values. Gear pumps have the same inconsistency problem, relying on meshing gears that begin to wear as soon as the pump is turned on. When volumetric consistency is compromised, flow rates go down while energy consumption goes up. Both centrifugal and gear pumps also create turbulence that can shear the pumped fluid, potentially altering or damaging the chemicals’ properties.

Not all AODD pumps may be best suited for specific applications, and the exact pump can vary depending on manufacturer, materials of construction, and configuration. For example, Almatec offers its E-Series Plastic AODD pumps in a plastic solid-body construction, which increases the pumps’ durability and strength in even the harshest environments. Each unique application merits careful consideration of the various pump options available and the extra benefits they may offer to provide the safest and most efficient handling of hazardous chemicals.


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