Process for metering liquid through serially connected pumps

Claim 1

In a process for metering liquid from a source into a material flowing through a vessel according to the flow rate of the material through the vessel including the step of pumping the liquid under pressure through a pipe from said source to said vessel through first and second gear pumps serially connected in said pipeline and driven by respective electric motors, said motors having control units for varying the speed thereof, the improvement comprising the steps of; a, continuously detecting the differential pressure across the second gear pump; b, generating a signal proportional to said differential pressure; and c, feeding said signal to the control unit of the first gear pump motor foR changing the speed of the first gear pump motor upon a change in differential pressure across the second gear pump whereby the first gear pump changes speed due to a change in back pressure on said second gear pump, said differential pressure thereby being maintained substantially constant.