Yes, air-operated double diaphragm (AODD) pumps are capable of meeting variable flow and differential pressures, but this requires the compressed air driving the pump to be variable. AODD pumps are a reciprocating positive displacement pump type. They are unique in that they are driven by compressed gas, typically air, which actuates diaphragms out of phase from one another. Therefore, their performance will be a function of the air volume and pressure supplied, which makes their performance characteristics different than other types of positive displacement pumps driven by constant speed electric motors.
When at a constant operating speed, positive displacement pumps typically deliver a nearly constant flow rate with slight flow variation due to increasing or decreasing pump differential pressure. To vary flow rate, the positive displacement pump’s rotational speed is typically adjusted. However, for AODD pumps, an electric motor is not used, so a variable supply air flow and pressure are plotted on the pump performance curve to show how the pump’s differential pressure and flow rate can vary. Image 1 is a generic representation of pump differential pressure as a function of pump flow rate for high and low air supply pressures. Additionally, to meet the flow rate, the air supply flow rate must be to the right of the high- and low-air pressure performance curves.
For additional information on pump performance, review Basic Pump & System Training offered by Pump Systems Matter at training.pumps.org. This training also helps when preparing for the Hydraulic Institute (HI)’s Pump System Certification (PSC) Level 1.
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