PURPOSE: To enable a cylinder and a gate vane both made of iron-base sintered substance to be prevented from wearing, by impregnating the surface of the gate vane made of iron-base sintered substance with an impregnant material made mainly of Fe3O4 and Cr2O3.

CONSTITUTION: A gate vane 11 is made of iron-base sintered substance, and its surface is impregnated with an impregnant material made mainly of Fe3O4 and Cr2O3. Thereby, high wear resistant fabric which is composed of the iron- base sintered substance, Fe3O4 and Cr2O3 is formed on the surface of the gate vane 11. Thereby, if a cylinder 1 made of iron-base sintered substance and the gate vane 11 are scrubbed together, abrasion loss of them can be reduced. Furthermore, wear of the cylinder 1 and the gate vane 11 can be further reduced, by impregnating the cylinder 1 with above-mentioned impregnant material or using high wear resistant aluminium-base alloy for rotor 10 and nitriding its surface.