A diaphragm pump has no piston or gears: a flexible membrane flexes back and forth, and a pair of one-way check valves turns that push-and-pull into a steady, single-direction flow.
A diaphragm pump (also called a membrane pump) is a positive-displacement pump that flexes a rubber or plastic membrane to move fluid. Because the fluid never touches a piston or seal, it can handle slurries, chemicals and abrasive liquids that would destroy other pumps.
The secret is the pair of check valves and how they team up with the diaphragm. Only with the body opened up can you see how the same chamber both sucks and pushes, and why no fluid flows backwards.
The motor turns an eccentric crank. On its pull stroke the rod drags the diaphragm away from the fluid chamber, making the chamber bigger and lowering the pressure inside.
With the chamber pressure lower than the inlet line, the inlet check valve lifts off its seat. Fluid is pushed in by the outside pressure; the outlet check stays firmly shut.
The crank now reverses and the rod pushes the diaphragm into the chamber. The trapped fluid is squeezed and the pressure rises.
Now the outlet check valve lifts while the inlet snaps shut, so the pressurised fluid can only leave through the outlet — never back down the inlet.
By opening and closing out of step, the two check valves turn the diaphragm's back-and-forth motion into a steady stream in one direction, and they keep the flow from ever reversing.
One lets fluid into the chamber and the other lets it out. Together they make the chamber act as a one-way pump, so fluid only ever moves in the intended direction.
A piston pump uses a sliding piston and often stuffing-box seals. A diaphragm pump uses a flexing membrane, and the fluid is fully sealed from the mechanism, so it can handle aggressive or gritty liquids.
Usually yes, briefly — it is not damaged the way many centrifugal pumps are by dry running. Its self-priming nature is one reason it is favoured for drawing liquids up from below.
Each stroke adds a small push, so the output naturally pulses. Some pumps stack two or more diaphragms, or add a damping chamber, to smooth it out.
Often a ball or a flap with an elastomer seat, chosen to suit the fluid. The soft seat is what lets the valve seal tightly even at low pressure.