The double-acting pressure reducing cylinder (1) includes a cylinder shaft (71) which cooperates with a double-acting pressure reducing piston (2) connected to transmission elements (3) housed in a transmission casing (8), while a hollow pillar (13) whose ends are articulated is traversed by a rod tunnel and bears against the casing (8) to support the shaft (71), a tie rod (17) likewise articulated traversing the tunnel to clamp the cylinder shaft (71) to the hollow pillar (13), while lower centering elements of the cylinder (20) and upper centering elements of the cylinder (21) integrated with the transmission casing (8) in particular via a centering frame (22) allow the cylinder shaft (71) to move freely in parallel with its longitudinal axis but not in the plane perpendicular to the axis.