Abstract: A leak detection system for monitoring an evacuated space which includes a vacuum pump, a low vacuum gauge for continuously monitoring the magnitude of the vacuum in said space, and a vacuum control switching assembly responsive to the vacuum in the space for periodically starting the pump when the vacuum in the space is lost to a predetermined extent, and thereby restoring the vacuum to a certain magnitude. A counter is provided to count cycles of the vacuum pump. An alarm device provides an alarm responsive to execessive running of the pump. A high vacuum test line is connected between the evacuated space and the vacuum pump. The high vacuum test line and vacuum pump are used concurrently with a switching system which opens to allow atmospheric air to be drawn into the evacuated space between the confining walls to sweep out and purge this space when high vacuum is applied to the evacuated space, and which isolates the sensitive low vacuum gauge at this time.