Abstract: An apparatus for regulating the fiber concentration of a fiber suspension during transport of the fiber suspension through a conduit which comprises a variable speed-controlled electric motor driving a pump for impelling the fiber suspension through the conduit to an outlet of the latter. A system is provided for obtaining a measure of the power supplied by the motor to the pump and for dividing this measure by a signal proportional to the flow rate of the fiber suspension in the conduit. The resulting signal, which is proportional to the fiber concentration in the fiber suspension, is employed to regulate the speed of the pump motor.

Abstract: The invention relates to a method of, and system for, degassing a mixture of a liquid first material, e.g. white water, and at least one second material, e.g. paper-making stock, the mixture being regeneratively pumped through cleaning means, e.g. a vortex cleaner, to an aeration tank. The regenerative pumping may be controlled to control the sub-atmospheric pressure applied to, and the liquid level in, the aeration tank.