The conversion of the PETRA storage ring at DESY to a third generation synchrotron radiation light source PETRAIII poses a challenge to the design of the beamline transport system. One of these challenges is to supply 15 beamlines and experiments windowless with the extremely collimated undulator radiation from the storage ring. The windowless connection causes the risk of accidental venting of the storage ring by experiments connected to the beamlines. To stop the inrush of such an accidental venting fast acting valve systems with closing times in the 10msec range are mandatory. The strong radiation background in the storage ring tunnel causes the need of all metal valves. A new small fast acting valve with an aperture of 40mm fitting to the strong collimated undulator beams and with a closing time < 10msec was developed. The all metal sealing principle achieves leak rates smaller than 10 mbarl/sec. This leak rate of the fast acting valve combined with a standard all metal valve prevents venting of the storage ring and the involved beam time losses for all beamlines. The mechanical and electronically layouts as well as first experiences with the new fast acting valve system developed for PETRAIII are presented.