AODD pumps are a dry, self-priming design that can handle relatively high suction lifts. Image 1 illustrates an AODD pump sectional with some important components labeled. The self-priming capability is the result of reciprocating diaphragms and inlet and outlet check valves that enable the evacuation of air from the liquid chamber and suction line without having to manually introduce liquid into the liquid chamber.
The maximum suction lift cannot be stated generally because it will depend on the fluid being pumped and how ideal the installation is. Fluid properties like higher viscosity and vapor pressure can limit the suction lift, as can installation considerations like suction pipe length and diameter. The limitation is primarily due to acceleration pressure and higher viscous losses in the suction piping that result in higher levels of vacuum, which—along with the static suction lift—can cause the pressure in the suction pipe or at the pump inlet to drop below the liquid’s vapor pressure, causing vaporization. Even though AODD pumps can handle vapor better than a centrifugal pump, vaporization makes it harder to lift the liquid and may result in the pump not achieving prime. Additionally, vapor pockets that form after priming can cause loss of prime or inconsistent flow.
To determine the suction lift capabilities, review the application in question with the pump manufacturer and follow their instructions with respect to suction piping to maximize the suction lift. To learn more about the priming and suction lift capabilities of AODD pumps, refer to American National Standards Institute (ANSI)/HI 10.1-10.5 Air-Operated Pumps for Nomenclature, Definition, Application and Operation.
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