Most AODD pump problems — premature diaphragm failure, poor flow rate, excessive air consumption, early seal wear — can be traced back to the selection stage. The wrong pump going into an application is a problem that no amount of maintenance will fix.
Here are the five factors that must be considered before specifying an AODD pump, and why each one matters.
The Fluid
The fluid being pumped determines the material selection for every wetted component — body, diaphragm, balls, ball seats, and O-rings. This is the first question to answer, not an afterthought.
Different fluids have different properties that require different material responses. A corrosive fluid like sulphuric acid 98% requires PVDF body and PTFE diaphragm. A fluid containing abrasive solids like coagulant or ceramic slurry requires an elastomer diaphragm rather than PTFE, because elastomers absorb abrasive impact far better than rigid PTFE. A flammable fluid in a hazardous area requires a conductive body material and ATEX certification. A shear-sensitive fluid like polymer solution requires a slower stroke rate and lower air pressure to minimise mechanical shear.
Wrong material selection is one of the three most common causes of premature AODD pump failure. It can also be a safety issue — using the wrong body material with a highly corrosive or flammable fluid is not just an operational problem.
Viscosity
The viscosity of the fluid — its resistance to flow — affects flow rate, pump efficiency, and installation design requirements.
AODD pump performance curves are published for water, which has a viscosity of approximately 1 centipoise (cps) at room temperature. Most industrial chemicals are similar in viscosity to water and can be assessed directly against the published pump curve. But fluids with significantly higher viscosity — heavy oils, concentrated polymers, adhesives — behave very differently. A pump sized purely on its water performance curve will underperform significantly when handling a viscous fluid.
Pump manufacturers publish viscosity correction curves that apply a derating factor to the published performance. For high-viscosity fluids, always apply this correction before selecting the pump size, and ensure the suction and discharge pipe design accommodates the increased flow resistance.
Flow Rate
Flow rate determines the pump size. The required flow rate — in litres per minute or cubic metres per hour — is the volume of fluid that needs to be moved within a given time. The larger the required flow, the larger the pump.
To determine which pump will deliver the required flow, refer to the pump performance curve. The curve shows flow rate as a function of discharge pressure (total dynamic head) and air supply pressure. The three variables are interdependent — changing one changes the others. Understanding this relationship is essential to selecting a pump that will perform as required under actual operating conditions, not just at a single idealised data point.
Viscosity must be factored in as described above. A pump selected for flow rate without accounting for fluid viscosity will not deliver the expected performance.
Operating Pressure
AODD pumps operate on a principle of pressure balance: the air pressure supplied to the pump determines the maximum discharge pressure the pump can generate. This is essentially a 1:1 ratio — a pump supplied with 4 bar of air pressure can generate a maximum discharge pressure of approximately 4 bar.
Before specifying a pump, you need to know the maximum air supply pressure available from the plant compressed air system. This sets the ceiling for what the pump can deliver. If the application requires a discharge pressure that exceeds what the available air supply can support, you are either looking at a different pump type or a larger air supply system.
Operating pressure also interacts with flow rate on the performance curve. As discharge pressure increases (more back pressure from the system), flow rate decreases. The selected pump must be able to deliver the required flow at the actual system pressure, not just at zero back pressure.
Pumping Temperature
Temperature is frequently the least-considered factor in AODD pump selection, but it has a direct and significant impact on material service life.
Elastomer diaphragms, O-rings, and plastic body materials all have temperature limits. Exceeding these limits — particularly with concentrated chemicals at elevated temperatures — accelerates degradation significantly. Santoprene diaphragms, for example, have good abrasion resistance but limited high-temperature performance. PTFE has excellent temperature resistance. PVDF handles temperatures above 100°C; polypropylene does not.
For pumping hot process fluids, check the temperature rating of every wetted component individually. A configuration that is chemically compatible may still fail prematurely if the operating temperature exceeds what the diaphragm or O-ring material can withstand.
The Right Pump for the Right Application
The Fluimac Phoenix AODD pump range covers connection sizes from 1/4 inch to 3 inch BSP/DN80, with body materials in polypropylene, PVDF, aluminium, and stainless steel 316, and diaphragm options across the full range of elastomers and PTFE. Getting the selection right across all five factors ensures the pump performs reliably and delivers the expected service life.
Autoflo Technology is the official distributor of Fluimac Phoenix AODD Pumps in Malaysia. For help with pump selection for a specific application, contact us at info@autoflotechnology.com.