Vacuum producing device

A vacuum producing device comprising:

• a principal suction nozzle unit able to be supplied by way of principal inflow duct with a pressure medium subject to a predetermined operating pressure, said pressure medium causing a suction effect, on flowing through the principal suction nozzle unit, in a principal suction duct adjoining a principal suction opening, said principal suction duct being connectable with a space to be evacuated, a shut-off valve being provided on the principal supply duct, said valve being actuatable in accordance with the negative pressure obtaining instantaneously in the space to be evacuated, said shut-off valve preventing flow of the pressure medium supply through the shut-off valve thereby interrupting the pressure medium supply to the principal suction nozzle unit when a predetermined target negative pressure is reached, wherein an additional suction nozzle unit is provided and connected in parallel functionally with the principal suction nozzle unit, such additional unit being constantly supplied during operation of the device with pressure medium subject to an operating pressure and such additional unit possessing an additional suction opening connected fluidwise with the principal suction duct of the principal suction nozzle unit, a check valve being provided between the two suction openings on the principal suction duct and being adapted to close oppositely to the direction of suction able to be caused by the principal suction nozzle unit.