Shut-off device for pipes

A shut-off device for pipes having a spindle connected to a shut-off element arranged in a housing, said spindle being borne in an upper part of the housing so as to be axially slidable, said upper part of the housing being provided with a cover resting on said housing, said cover having an interior space communicating with a medium led through the housing,

• said spindle (40) being provided at its lower end facing the shut-off element (80) with a ring (60) carrying at least two concentrically arranged expansion bellows defining an inner expansion bellows (70) and an outer expansion bellows (50), said inner expansion bellows being connected to said spindle,
• characterized in that said outer expansion bellows (50) is connected to a flange (11b) of the cover of the housing (11), the shut-off element (80) slides said ring (60) along the spindle (40) in a sleeve-shaped cover body (11c) of the housing cover (11) until it abuts against a stopper (18) in the cover body (11c), said inner bellows (70) is pre-tensioned on pressure while said outer bellows (50) is pre-tensioned on tension when the shut-off device for pipes (1) is closed, and when said ring comes to abut on the stopper (18) said inner bellows (70) is submitted to tensile load while said outer bellows is submitted to pressure load.