The RUVAC WH / WHU series is equipped with a hermetically sealed motor without shaft seals and with an integrated water cooling facility. Moreover, it is provided with a purge gas option qualifying it for pumping corrosive and toxic gases. The RUVAC WHU types are equipped with an integrated bypass line incorporating a newly developed control flap. Thus the pumps can be started at atmospheric pressure and the pump down times in short cycle operation are considerably reduced.