When laboratory ground devices are used under vacuum or/and slight overpressure, the use of this combined overpressure safety valve can be recommended. These valves act as immediately closing safety valve under vacuum and they allow under overpressure the visual control of the bubble formation in the blocking liquid. The real sealing is effected by a special designed spherical ground joint (cup and ball) on which an adjustable spring power acts. It is supported by a free to chose blocking liquid which should be higher viscous for vacuum operations. The sealed climbing tube at the spherical ground cup serves as a guide and prevents that the liquid climbs back into the apparatus.