What is the principle of vacuum tube for valve cover of MG 3 engine?

Using the principle of vacuum assisted braking.

Vacuum tube is a kind of negative pressure produced by air intake when throttle valve is closed, commonly known as vacuum. Use this vacuum to help brake. Because the braking of a car requires a certain amount of force, using vacuum power can make the operation very easy.

Vacuum tube is a kind of negative pressure produced by air intake when throttle valve is closed, commonly known as vacuum.