768,537. Centrifugal separators. FREEMAN H., and BOADWAY, J. D. April 27, 1955 [April 27, 1954], No. 12193/55. Addition to 740,588. Class 23 In a method of separating gases and other impurities from a liquid comprising injecting the liquid into a chamber 13 to form a hollow vortex 15, reversing part of the vortex 15 to form a second vortex 20, and reversing part of the vortex 20 to form a third vortex 35 enclosing a gas core 14, the impurities are discharged with the remaining part of the vortex 15, the purified liquid in the remaining part of the vortex 20, and the gas is withdrawn at a rate to maintain a sub-atmospheric pressure in the core. Paper pulp, tangentially injected into the chamber 13 by a nozzle 10, is guided within the chamber by a spiral guide 12 to form the vortex 15. On reaching the bottom section 16 part of the vortex 15 is reversed to form the vortex 20 and the remainder of the vortex 15 carries dirt to the outlet 18. The vortex 20 passes upwardly through the vortex finder 21 to meet a conical projection 27 which reverses a part of the vortex to form the vortex 35 whilst the purified pulp forming the remainder of the vortex 20 passes through an annular gap 29 to a chamber 30 from whence it is discharged by a tangential outlet 32. The vortex 35, which contains gas bubbles, is discharged with the dirty pulp through the outlet 18. As shown, the outlet is connected to a pipe 36 shaped to give an eduction effect which permits discharge to atmosphere, but the outlet may be connected to a vacuum pump particularly if it is desired to remove dissolved gases. In a modification (Fig. 9, not shown) the outlet 18 discharges axially into the upper part of a chamber similar to the chamber 13 and to which water is supplied through the tangential inlet so that the eduction effect on the outlet is increased and the dirty pulp is diluted. In the modification, shown in Fig. 7, the outer part of the vortex 20 1 , constituting the purified pulp, is discharged through perforations in a cylindrical extension 40 of the vortex finder 21 1 to a chamber 42 having an outlet 43. In the separating plant shown in Fig. 8 three separators 13 discharge dirty pulp into a vacuum chamber 46, the dirty pulp from the chamber 46 being separated, after dilution in a further separator 52 and the purified pulp from the separator 52 being returned to the separators 13. Dimensions of the section 16 are given in the Specification.