What type of primer makes use of the vacuum in the intake manifold of a gasoline engine?

Vacuum primers utilize the vacuum created in the intake manifold of a gasoline engine to facilitate the priming process. This mechanism works by using the negative pressure generated during the intake stroke of the engine to draw fuel from the tank into the fuel line and into the carburetor or fuel injectors. When the engine starts, it creates a vacuum that helps pull fuel into the system, ensuring proper fuel delivery for combustion.

The design of vacuum primers is particularly advantageous because it relies on existing engine mechanics, which means it doesn’t require additional electrical components or mechanisms to operate. This can make the system simpler and more reliable in many applications, especially in fire apparatus where quick and reliable fuel delivery is critical.