خزان التفريغ مسرّب

The reservoir storing vacuum for vacuum-operated devices, leaking so it cannot hold a charge. Its whole purpose is to store, so a leak defeats it entirely even though the pump or the manifold may be producing vacuum perfectly well.

The signature is a supply that is adequate while the engine is running and gone when it is needed. Devices work under some conditions and not others, and the auxiliary vacuum pump runs far more often than it should — a pump cycling frequently is the audible clue and points at storage rather than generation.

On engines with little manifold vacuum this matters most, since there is nothing to fall back on. The reservoir is usually a moulded plastic vessel that cracks at a seam or a spigot, or corrodes if it is steel, and its check valve is the other failure point. Test it by applying vacuum with a hand pump and watching it hold — that separates a leaking reservoir from a leaking check valve or a device downstream in one measurement.