Pressure Carburetor - Construction

Construction

Like a float carburetor, a pressure carburetor has a barrel with a venturi inside it through which air flows on its way to the engine cylinders. However, it does not have a float to control the flow of fuel into the carburetor. Instead, it has four chambers in a row separated by flexible diaphragms. The diaphragms are attached concentrically to a shaft which operates a wedge-shaped servo valve. This valve controls the rate at which fuel can enter the pressure carburetor. Inside the barrel, downsteam of the throttle sits the discharge valve, which is a spring-loaded valve operated by fuel pressure that controls the rate that fuel is discharged into the barrel.

Some pressure carburetors had many auxiliary systems. The designs grew in complexity with the bigger models used on bigger engines. Many have an accelerator pump, an automatic mixture control, and models on turbocharged engines feature a temperature compensator. The result is that pressure carbureted engines are fairly simple to operate compared to float carbureted engines.