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Manifold vacuum, or engine vacuum in a petrol engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the airflow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of ...
The system usually consists of a tube, a one-way valve and a vacuum source (such as the inlet manifold). The unwanted gases, called "blow-by", are gases from the combustion chamber which have leaked past the piston rings. Early engines released these gases to the atmosphere simply by leaking them through the crankcase seals.
Vacuum Modulator is an engine load sensing device that converts engine vacuum into a transmission valve body input.. Most vacuum modulators operate with manifold vacuum (below throttle blades) that offer more vacuum at idle, and proportionately changes (rises and falls) with engine load as opposed to operating on engine speed.
The vacuum is only an assist and the brakes can still function, requiring greater force, if the booster vacuum is used up. Many older vehicles used vacuum-powered windshield wipers. Loss of manifold vacuum when the engine was working hard, or at wide open throttle, necessitated using a vacuum booster pump which was usually part of the fuel pump.
Some early gas engines worked on the "vacuum" or "atmospheric" principle in a similar way to the Newcomen steam engine.A mixture of gas and air was eaten by the cylinder and ignited; the mixture expanded and part of it escaped through the exhaust valve; the valve then closed, the mixture cooled and contracted, and atmospheric pressure pushed the piston in.
A vacuum hose connected to the intake manifold downstream of the throttle provides a reference pressure for the blowoff valve.. When the throttle is open, the air pressure on both sides of the blowoff valve's piston is equal, therefore the spring holds the valve closed.
The ACIS/TVIS System. Acoustic Control Induction System, or ACIS, is an implementation of a variable-length intake manifold system designed by Toyota.. Simply put, the ACIS system uses a single intake air control valve located in the intake to vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency and reduce intake "roar".
Engines fitted with a decompressor can also be stopped by operating the decompressor, and in a vehicle with a manual transmission it is sometimes possible to stop the engine by engaging a high gear (i.e. 4th, 5th, 6th etc.), with foot brake and parking brake fully applied, and quickly letting out the clutch to slow the engine RPM to a stop ...