Hydraulic system, in particular for a mixing apparatus, comprising: - a hydraulic cross connection, housed in a housing case configured to be mounted on a rear planar support, the housing case comprising one or more supporting rear elements, each one having a free supporting end configured to rest on the rear planar support when the housing case is mounted on the same rear planar support, the hydraulic cross connection comprising one or more ducts (70, 71), a seat being obtained on an outer wall of each one of said one ore more ducts (70, 71), - at least one tubular element (105, 106) having a longitudinal tube removably insertable in each one of said one or more ducts (70, 71), the longitudinal tube externally comprising a circular notch, having a depth, delimited by ends of two portions of the longitudinal tube adjacent to the circular notch, - at least one quick coupling removable hook (91; 991), configured to be inserted in the seat obtained on an outer wall of each one of said one or more ducts (70, 71), said at least one removable hook (91; 991) comprising at least one first front elastic arm (93, 94) and at least one second front elastic arm (93, 94) configured to interact with the seat and with the ends of the two portions of the longitudinal tube delimiting the circular notch of the longitudinal tube when inserted in one of said one or more ducts (70, 71) to which the seat belongs for locking the longitudinal tube, the hydraulic system being characterised in that said at least one quick coupling removable hook (91; 991) is configured to be posteriorly inserted in the seat and it comprises at least one rear arm (95; 995), and in that a distance separating the seat of each one of said one or more ducts (70, 71) from a planar surface passing through each free supporting end of said one or more supporting rear elements of the housing case ranges from a minimum value equal to the minimum distance sufficient for housing said at least one rear arm (95; 995) when said at least one removable hook (91; 991) is inserted in the seat, including such minimum value, and a maximum value equal to the sum of the minimum distance sufficient for housing said at least one rear arm (95; 995) when said at least one removable hook (91; 991) is inserted in the seat with said depth of the notch of the longitudinal tube when inserted in one of said one or more ducts (70, 71) to which the seat belongs, excluding such maximum value, whereby said at least one removable hook (91; 991) is removable from the seat and the longitudinal tube is extractable from the duct (70, 71) to which the seat belongs only when the housing case is not mounted on the rear planar support. - a hydraulic cross connection, housed in a housing case configured to be mounted on a rear planar support, the housing case comprising one or more supporting rear elements, each one having a free supporting end configured to rest on the rear planar support when the housing case is mounted on the same rear planar support, the hydraulic cross connection comprising one or more ducts (70, 71), a seat being obtained on an outer wall of each one of said one ore more ducts (70, 71), - at least one tubular element (105, 106) having a longitudinal tube removably insertable in each one of said one or more ducts (70, 71), the longitudinal tube externally comprising a circular notch, having a depth, delimited by ends of two portions of the longitudinal tube adjacent to the circular notch, - at least one quick coupling removable hook (91; 991), configured to be inserted in the seat obtained on an outer wall of each one of said one or more ducts (70, 71), said at least one removable hook (91; 991) comprising at least one first front elastic arm (93, 94) and at least one second front elastic arm (93, 94) configured to interact with the seat and with the ends of the two portions of the longitudinal tube delimiting the circular notch of the longitudinal tube when inserted in one of said one or more ducts (70, 71) to which the seat belongs for locking the longitudinal tube,