A diaphragm pump moves fluid by flexing a flexible membrane back and forth inside a chamber. On the suction stroke, the diaphragm pulls away from the chamber, creating a low-pressure region that opens an inlet check valve and draws fluid in. On the discharge stroke, the diaphragm pushes back, closing the inlet valve and forcing fluid through the outlet check valve. The pumped fluid only touches the diaphragm, the check valves, and the chamber wetted surfaces — never any shaft, seal, or bearing.

That isolation is the whole point. Because there's no rotating shaft passing into the pumped fluid, there's no dynamic seal to leak. This makes diaphragm pumps the default choice for:

• Hazardous or toxic fluids — chemical dosing, acids, solvents
• Abrasive slurries — mine tailings, ceramic slips, drilling mud
• Shear-sensitive fluids — latex, food products, biological suspensions
• Sanitary applications — pharmaceuticals, dairy (with PTFE or EPDM diaphragms)
• Self-priming duty — they can pump air, so they'll evacuate a suction line on startup

Actuation types: Mechanically actuated pumps use a crankshaft or eccentric — simple but limited to low pressures. Air-operated double diaphragm (AODD) pumps use compressed air alternately on the back side of two linked diaphragms; they're the workhorse of industrial transfer duty because they stall safely against a closed valve (no overpressure, no motor overload). Hydraulically actuated diaphragm pumps use oil behind the diaphragm and can hit 5,000+ psi for metering applications.

Rule of thumb for AODD sizing: Flow rate is roughly proportional to inlet air pressure and inversely proportional to discharge pressure. Air consumption is typically 1 to 1.5 SCFM per GPM of water at moderate discharge pressures. So a pump moving 20 GPM will burn through 20–30 SCFM of compressed air — meaning you often need a much bigger compressor than the pump nameplate suggests. This is why AODD pumps are cheap to buy but expensive to run: compressed air is one of the least efficient energy carriers in a plant.

Real-world example: A paint manufacturing plant transfers thick pigment dispersions from mixing tanks to filling lines. An AODD pump with EPDM diaphragms handles the shear-sensitive paint without damaging it, self-primes when tanks run low, and safely dead-heads when the filling line pauses — no controls, no VFD, no seal maintenance. When operators want more flow, they open the air regulator.

Diaphragm life is the failure mode to watch. Every stroke flexes the membrane; fatigue eventually cracks it. PTFE lasts longest chemically but flexes poorly; elastomers like Santoprene flex well but have narrower chemistry compatibility. Expect 10–100 million cycles depending on material, pressure, and temperature.