A valve for controlling a flow of fluid, the valve having: a housing with a flow channel extending through the housing from a first end in an axial direction to a second end, the flow channel having a first flow channel section extending into the valve from the first end and a second flow channel section extending into the valve from the second end; a bulb suspended in said second flow channel section via at least one bridge connecting said bulb to said housing, said second flow channel section passing radially outside of said bulb except where said at least one bridge is located and said first flow channel section extending axially from said first end to said bulb; an obturator sheath suspended for guided axial movement between a closed position and an open position; wherein the obturator sheath in the closed position closes off at least one flow passage between the first flow channel section radially inside the at least one flow passage and the second flow channel section radially outward of the at least one flow passage, substantially blocking flow from the first flow channel section to the second flow channel section and vice versa; wherein the obturator sheath in the open position at least partially leaves open the flow passage between the first flow channel section and the second flow channel section, allowing flow from the first flow channel section to the second flow channel section and vice versa; an operating member extending axially in the bulb and connected to the obturator sheath, the operating member having at least one engagement surface (18, 19) facing in axial direction; a toggle member pivotably mounted to the bulb so as to be pivotable about a pivot axis between a closing position causing the obturator sheath to be in the closed position and an opening position causing the obturator sheath to be in the open position, the toggle member having at least one actuating surface (22, 23) in contact with the at least one engagement surface (18, 19) in a position in a plane spaced from the pivot axis in a direction perpendicular to the axial direction and to the pivot axis; characterized in that, the at least one actuating surface (22, 23) has at least first and second surface portions (22a, 23a; 22b, 23b) at mutually different distances from the pivot axis and contiguous to each other, said first and second surface portions (22a, 23a; 22b, 23b) having mutually different radii of curvature about axes of curvature parallel to the pivot axis. a housing with a flow channel extending through the housing from a first end in an axial direction to a second end, the flow channel having a first flow channel section extending into the valve from the first end and a second flow channel section extending into the valve from the second end; a bulb suspended in said second flow channel section via at least one bridge connecting said bulb to said housing, said second flow channel section passing radially outside of said bulb except where said at least one bridge is located and said first flow channel section extending axially from said first end to said bulb; an obturator sheath suspended for guided axial movement between a closed position and an open position; wherein the obturator sheath in the closed position closes off at least one flow passage between the first flow channel section radially inside the at least one flow passage and the second flow channel section radially outward of the at least one flow passage, substantially blocking flow from the first flow channel section to the second flow channel section and vice versa; wherein the obturator sheath in the open position at least partially leaves open the flow passage between the first flow channel section and the second flow channel section, allowing flow from the first flow channel section to the second flow channel section and vice versa; wherein the obturator sheath in the closed position closes off at least one flow passage between the first flow channel section radially inside the at least one flow passage and the second flow channel section radially outward of the at least one flow passage, substantially blocking flow from the first flow channel section to the second flow channel section and vice versa; wherein the obturator sheath in the open position at least partially leaves open the flow passage between the first flow channel section and the second flow channel section, allowing flow from the first flow channel section to the second flow channel section and vice versa; an operating member extending axially in the bulb and connected to the obturator sheath, the operating member having at least one engagement surface (18, 19) facing in axial direction; a toggle member pivotably mounted to the bulb so as to be pivotable about a pivot axis between a closing position causing the obturator sheath to be in the closed position and an opening position causing the obturator sheath to be in the open position, the toggle member having at least one actuating surface (22, 23) in contact with the at least one engagement surface (18, 19) in a position in a plane spaced from the pivot axis in a direction perpendicular to the axial direction and to the pivot axis; characterized in that, the at least one actuating surface (22, 23) has at least first and second surface portions (22a, 23a; 22b, 23b) at mutually different distances from the pivot axis and contiguous to each other, said first and second surface portions (22a, 23a; 22b, 23b) having mutually different radii of curvature about axes of curvature parallel to the pivot axis.