What device uses the vacuum in the intake manifold on a gasoline engine?

The vacuum primer is a device specifically designed to utilize the vacuum created in the intake manifold of a gasoline engine to facilitate fuel delivery, particularly in applications where fuel needs to be primed into the system before starting. When the engine is cranked, the vacuum in the intake manifold draws fuel from the tank into the carburetor or fuel injection system, ensuring that the engine has a sufficient supply to start and run efficiently.

This device takes advantage of the changes in pressure created by the engine's operation, providing a simple and effective means of supplying fuel without the need for additional mechanical pumps. Understanding this mechanism is vital, especially in fire apparatus, where reliable engine performance is crucial for operational readiness.

In contrast, devices like the exhaust primer, pressure governor, and relief valve serve different functions. The exhaust primer is used to introduce fuel into the exhaust system to aid in starting diesel engines, while a pressure governor regulates the pressure within a system. The relief valve, on the other hand, ensures that excessive pressure does not accumulate, typically for safety purposes. Each of these devices plays a unique role in engine operation but does not utilize the intake manifold vacuum in the same manner as the vacuum primer.