Here's how engine vacuum works in a typical gasoline-powered car:
The engine vacuum is a byproduct of the piston's downward stroke during the intake phase. Here's a breakdown:
1. Intake Stroke: The piston moves downward, creating a low-pressure area (partial vacuum) in the cylinder. This lower pressure is relative to atmospheric pressure outside the engine.
2. Air Intake: This low pressure sucks air (and fuel) into the cylinder through the intake manifold. The greater the pressure difference between the cylinder and the atmosphere, the stronger the vacuum.
3. Manifold Vacuum: This partial vacuum isn't confined to just the cylinders. It extends throughout the intake manifold, creating what is known as "manifold vacuum." This vacuum is the engine's vacuum.
4. Vacuum-Operated Systems: Many systems in the car utilize this manifold vacuum to operate. This includes:
* Brake Booster: Assists the driver in braking by multiplying the force applied to the brake pedal.
* Power Steering (in some older systems): Assists in steering, although most modern cars use electric power steering.
* Vacuum-operated distributor advance: Adjusts the timing of the spark to optimize engine performance.
* Climate Control Systems (some components): May use vacuum for things like controlling vents or recirculation.
* Cruise Control (some older systems): Some older cruise control systems relied on vacuum.
5. Measurement: Manifold vacuum is measured in inches of mercury (inHg) or kilopascals (kPa). A healthy engine will typically have a fairly strong vacuum at idle. A low vacuum often indicates a problem somewhere in the engine or intake system (e.g., a leak, faulty valve, etc.).
In short, engine vacuum is a consequence of the engine's normal operation – the act of drawing air into the cylinders. It's a readily available source of power used to operate various vehicle systems.
