A check valve for a vacuum booster holds vacuum pressure and assures power assist capability when ___________________.

The function of a check valve in a vacuum booster is to maintain the vacuum pressure necessary for providing power assistance during braking. When the engine is operating normally, it generates a strong vacuum that allows the booster to amplify the driver’s braking force. However, if there is a low engine vacuum, the check valve helps ensure that the existing vacuum is retained within the booster. This is critical because it allows the power assistance capability to remain functional even during periods of reduced vacuum, such as under heavy engine load or during certain driving conditions. By holding the vacuum, the check valve effectively prevents any unnecessary loss of power assist, ensuring that the brakes remain responsive when needed.

Maintaining this vacuum is paramount for the system’s reliability, as a loss of vacuum pressure could lead to a reduction or complete loss of power assist, greatly affecting braking performance.