Automobile Engineering in ME
The condition that causes vapour locking in a brake system is

Keeping the vehicle without use for an extended period
An excessively high engine speed on a downhill road
Overcooling of the brakes during high speed driving
Overheating of the fluid due to frequent brake application

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Automobile Engineering in ME
The function of a first compression ring (top ring) is that it

Increases the combustion temperature
Maintains a seal and prevents the fuel leakage
Maintains a seal and prevents escape of burned gases and loss of pressure in the combustion chamber
Creates swirl

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