A device for carrying out liquid treatment of a fiber pulp suspension to form a running fiber web includes an arc-shaped duct having various portions. The first portion has a converging cross-section for compressing the fiber pulp suspension to form the fiber web. The second portion has a diverging cross-section for the expansion of the fiber web and includes a liquid-treatment zone. The third portion has a converging cross-section for compressing the fiber web. Along its length, the duct is defined inwardly by a rotary cylindrical screen member and radially outwardly by a stationary wall member.