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How to choose an AODD pump
A quick guide to selecting the correct AODD pump for your specific application
When deciding on which Air Operated Double Diaphragm (AODD) pump to select for a particular application, the first crucial question to ask is what material is being pumped? More specifically, what is the material’s solid content, pH level, viscosity, density and specific gravity, and is the material abrasive? All these considerations have a major impact on the compatibility of the material with the pump.
Aluminium for example offers only medium corrosion and abrasion resistance and is not suitable for halogenated hydrocarbons, while polypropylene has a much wider chemical compatibility. However, polypropylene has a limited temperature range, so for higher temperatures other materials need to be chosen. PVDF (Kynar) displays strong chemical resistance of acids and bases, a good abrasion resistance and high temperature resistance. PTFE displays the widest chemical compatibility, extreme corrosion resistance, has a very low frictional coefficient, is non-adhesive, provides high heat resistance, but offers poor abrasion resistance. Another key material for AODD pumps is Santoprene, which offers good abrasion and chemical resistance, and suitability for use with some solvents, caustic solutions, dilute acids, and alcohols.
The next consideration is the application. What flow rate do you need, where is the feed tank relative to the pump, and what is the overall suction length, vertical rise, and discharge distance? All these play a role in determining the inlet and outlet hose diameter.
Whether a pump with an ATEX certification is necessary or not also has an influence. If not, then a polypropylene or PVDF pump can be chosen. If ATEX certification is needed then a conductive polypropylene offers chemical resistivity at a low cost, while Hastelloy offers even higher resistance to chemicals, is mechanically robust, but is expensive.
Let’s now consider what type of AODD pump to select for specific applications.
Paint circulation and transfer
A challenge with this application is that a very long hose length is often required, sometimes up to 250 meters, so it’s important to get the right combination between fluid pressure and volume. Paint suspension is another challenge. For example, metallic paints or zinc epoxies need to remain in suspension, which rules out a pressurized system. Moreover, paint is sensitive to shear, so a pump needs to be selected that avoids shear. A typical Graco solution for paint circulation and transfer is a Husky 716, 1050, 1590, 2150, 3300 or 1050e model. The wetted section is metal, the diaphragms PTFE (over-molded or 2-piece) and Santoprene, and the seats constructed from polypropylene, Santoprene, PVDF or stainless steel.
Graphite transfer in pipe manufacturing
During the manufacturing process of a pipe, graphite needs to be transferred as a lubricant to the mandrel. The graphite in powder form is mixed with water. Challenges include a high application temperature, and a material that is viscous, thixotropic and abrasive. A conventional piston pump is no use for this application as it will separate the graphite from the water and clog the pump. The Graco solution would be a Husky 2150 aluminium pump with a 2-inch outlet pipe, stainless steel balls, and a Santoprene diaphragm.
Pumping an injectable gel inside a wall
Such an application is common in the construction industry, for example to control moisture in a cellar. Controlled manual dispensing is necessary of a highly viscous material. Low pumping volume and low pressure is used to inject the gel. If a material such as Siloxane is used, the pump should be corrosion resistant. Graco recommends its Husky 307 Acetal pump, which has an acetal body for corrosion resistivity along with PTFE inner parts. Acetal offers wide solvent resistance and withstands extreme fatigue while offering a good level of abrasion resistance.
Chemical transfer in heap leaching
To extract minerals from stone, the crushed ore heap is sprinkled with an acid (e.g. sulfuric) that penetrates the ore and dissolves the minerals. The leach solution then needs to be pumped into the mixing and separation process. Obviously the key requirement is for a pump that resists strong acids and cyanide solutions. It should also provide high flow, as large quantities of acids are used, while a leak-free design is essential to avoid contamination of the environment. A good solution is a 2-inch Graco Husky pump with a stainless steel center and fluid section, and Santoprene inner parts. A polypropylene center and fluid section is also possible. For higher flow rates a 3-inch pump would be preferable.
Metal plating
This application concerns the plating of small metal components with protective or decorative coatings of zinc. AODD pumps are suitable for this application, and are used for the transfer of the plating material from the chemical kitchen to the dipping tanks and back to the kitchen where the sludge is separated from the coating material and further processed through a filter press. The main requirements are chemical compatibility and a leak-free design. Fitting the bill is a Graco Husky 1050, 1590 or 2150 pump with a PVDF body and PTFE inner parts. When a sodium hydroxide bath is included, the pump should have a polypropylene body and Santoprene inner components.
Ceramics
The challenge faced by pumps in the ceramics industry is the presence of highly abrasive, high viscosity ceramic slips and slurries which have to be transferred in large volumes. Generally a 1”, 1½” or 2” aluminium pump is suitable. The wetted section can be metal or plastic, with Santoprene balls, stainless steel seats, and Geolast or Santoprene diaphragms. For larger castings the larger size pumps should be selected.
Ask Graco for specific information
Graco provides a wealth of information and tools to help you decide which AODD pump to select for each specific application.
For example, Graco’s detailed Materials of Construction Guide outlines all the materials commonly used in the manufacture of AODD pumps, along with their temperature range and an indication of price. It indicates whether each material is suitable for mild chemicals, aggressive chemicals, high temperatures and abrasives.
Graco also provides pump performance charts to help you determine what the air consumption will be at a certain fluid pressure and flow, as well as an online diaphragm pump selector tool at www.graco.com/husky.
For specific questions, fill in the below form.
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