How Does a Diaphragm Carburetor Work?
In most ways, a diaphragm carburetor works exactly like other carburetors but with a unique mechanism for maintaining fuel levels inside the fuel chamber. Unlike a float chamber carburetor, which uses a simple inlet valve to maintain a constant reservoir of fuel, a diaphragm carburetor sequesters gasoline behind a diaphragm mounted to a needle valve. The advantage to this arrangement is that the fuel can be delivered regardless of orientation.
In a diaphragm carburetor, such as those used by portable gasoline engines, powered hand tools and piston-engine aircrafts, gasoline is delivered by the fuel pump to the carburetor, but it is not immediately admitted to the fuel chamber. Instead, it is blocked by a diaphragm that flexes inward and outward in response to pressure inside the mixing chamber. As it flexes, the diaphragm pushes against a needle valve. As this valve opens and closes, it admits or restricts the flow of gasoline into the chamber. When pressure inside the chamber is low, the diaphragm flexes forward, pushes on the needle valve, opens the aperture and admits gasoline. As fuel fills the chamber, pressure is equalized, the diaphragm returns to its resting position, and the valve closes to slow the flow of fuel.