The fast valve is positioned immediately downstream of the slow valve. This all-metal-seal fast valve closes in as little as 5 to 9 ms, thereby retarding the advance of a pressure wave progression upstream. This valve, however, does not seal and cannot support even instantaneous exposure to a full photon beam without physical damage. Therefore, it is interlocked to the photon shutter (PS1) during operation.

On vacuum failure, the photon shutter (PS1) is activated, which triggers immediate beam dump. Once the photon shutter mechanism is down, the fast valve closes, followed by the closing of the slow valve.

The MOM-Vacuum group is currently working on removing all Front End Fast Valves which have become problematic over time.