How to Select AODD Pump Diaphragm Material by Fluid Chemistry: PTFE, Santoprene & 7 Common Options

In an air-operated diaphragm pump, the diaphragm both contacts the pumped fluid directly and flexes continuously with every air stroke. It is therefore not possible to select a material based on a single factor alone. When evaluating a diaphragm material for a specific fluid, consider all of the following simultaneously:

• Chemical compatibility — will the material swell, blister, or degrade on contact with the pumped fluid? This is the first elimination criterion.
• Temperature range — low temperatures make rubber brittle, high temperatures soften the material and reduce its mechanical properties. Each material has its own limiting range.
• Abrasion resistance — for fluids containing solid particles, slurries, slimes, or crystals, diaphragm abrasion durability determines replacement frequency.
• Flex life — the number of cycles the diaphragm can endure before fatigue and cracking. More flexible materials generally have better flex life, but typically trade off chemical resistance.

!A material that performs well on one criterion often falls short on another. PTFE offers broad chemical resistance but is stiff with lower flex life; conversely, Santoprene/EPDM are flexible and tough but limited against strong solvents. Always eliminate first by chemical compatibility, then weigh temperature and abrasion.

The table below summarizes the characteristics of common AODD diaphragm materials based on Sandpiper technical documentation and general industry material standards. Use it as a quick filter, then cross-reference the chemical compatibility chart for your specific fluid.

!Temperature figures are for general reference only. Actual limits depend on chemical concentration, pressure, and the specific pump configuration — always cross-reference the manufacturer’s compatibility chart before finalizing your selection.

To shorten the selection process, common situations encountered in Vietnamese industrial plants can be grouped as follows:

• Strong acids and bases, solvents: PTFE is preferred for its broad chemical resistance spectrum. Because PTFE is less flexible, designs typically add a backing diaphragm to compensate for flex life.
• Fluids with solid particles, slurries, slimes, abrasive crystals: Santoprene or Buna-N offer a good balance between abrasion resistance and flex life.
• Oil-based fluids, greases, fuels: Buna-N (Nitrile) or Geolast provide good oil resistance and adequate mechanical durability.
• Hot water, steam, water-based chemicals: EPDM is flexible and resistant in hot water-based environments.
• Aggressive chemicals at high temperatures: Viton (FKM) withstands harsh conditions; note that flex life and abrasion resistance are more limited, requiring an appropriate maintenance plan.

Air-operated diaphragm pumps have structural advantages that support this: their seal-less design, self-priming capability, safe dry-run operation, and low shear forces allow them to handle viscous, particle-laden, or abrasive fluids that many other pump types struggle with.

Selecting the diaphragm is the first step, but the valve assembly and housing material must also be compatible with the pumped fluid:

• Ball valve: suited to most clean fluids or fluids with small particles, seals well and is the standard choice.
• Flap valve: provides a wider flow passage, suited for thick, viscous fluids or fluids containing large solid particles that tend to jam ball valves.
• Pump housing: aluminum for neutral fluids at low cost; SS316 for corrosive chemicals and food-grade applications; PP/PVDF for acids/bases; cast iron for heavy-duty applications.

Air supply pressure for diaphragm pumps typically falls in the range of 1.4–8.6 bar. For applications requiring reduced compressed air consumption, the electric EODD diaphragm pump is an alternative that lowers air usage compared to conventional pneumatic configurations.