Density meter for slurry which is transported through pipes, the density meter comprising: - a housing having, on opposites sides of the housing, two flanged pipe couplings (3, 4, 5, 6) for coupling of a feed pipe and a discharge pipe; - a pipe part housed in the housing and extending between and spaced apart from the two flanged pipe couplings (3, 4, 5, 6); - a flexible sleeve having on both ends a flange (10, 11), which flexible sleeve extends through both pipe couplings (3, 4, 5, 6) and the pipe part and wherein the flanges (10, 11) of the flexible sleeve abut against the flange of the respective flanged pipe coupling (3, 4, 5, 6); and - a sensor arranged to the pipe part and computing means for computing the density of the slurry in the pipe part at least on the basis of the volume of the pipe part and measurements of the sensor; wherein each flange (10, 11) of the flexible sleeve has an inner annular portion of a first thickness (t 1) characterized in that each flange (10, 11) of the flexible sleeve has an outer annular portion of a second thickness (t 2), wherein the first thickness (t 1) is smaller than the second thickness (t 2); and in that a spacer ring is provided around each flange (10, 11) of the flexible sleeve and wherein the spacer ring abuts against the flange of the respective flanged pipe coupling (3, 4, 5, 6), which spacer ring has a thickness of the first thickness (t 1) or less, wherein the flexible sleeve is of a reinforced rubber, such as natural rubber or Styrol Butadiene Rubber with embedded nylon cords, and wherein a number of cord loops extend in the axial plane partially out of the outer annular portion. - a housing having, on opposites sides of the housing, two flanged pipe couplings (3, 4, 5, 6) for coupling of a feed pipe and a discharge pipe; - a pipe part housed in the housing and extending between and spaced apart from the two flanged pipe couplings (3, 4, 5, 6); - a flexible sleeve having on both ends a flange (10, 11), which flexible sleeve extends through both pipe couplings (3, 4, 5, 6) and the pipe part and wherein the flanges (10, 11) of the flexible sleeve abut against the flange of the respective flanged pipe coupling (3, 4, 5, 6); and - a sensor arranged to the pipe part and computing means for computing the density of the slurry in the pipe part at least on the basis of the volume of the pipe part and measurements of the sensor; wherein each flange (10, 11) of the flexible sleeve has an inner annular portion of a first thickness (t 1) characterized in that each flange (10, 11) of the flexible sleeve has an outer annular portion of a second thickness (t 2), wherein the first thickness (t 1) is smaller than the second thickness (t 2); and in that a spacer ring is provided around each flange (10, 11) of the flexible sleeve and wherein the spacer ring abuts against the flange of the respective flanged pipe coupling (3, 4, 5, 6), which spacer ring has a thickness of the first thickness (t 1) or less, wherein the flexible sleeve is of a reinforced rubber, such as natural rubber or Styrol Butadiene Rubber with embedded nylon cords, and wherein a number of cord loops extend in the axial plane partially out of the outer annular portion.