A sub-sea mud pump system includes a plurality of pump units, and each pumping
unit includes a plurality of pumping elements. Each pumping element includes a
pressure vessel with a first and a second chamber, a separating member between
the first and second chambers, a measurement device adapted to measure the volume
of at least one of the first and second chambers, a hydraulic inlet control valve
and a hydraulic outlet control valve coupled to the first chamber, a mud suction
valve and a mud discharge valve coupled to the second chamber. The first chamber
is hydraulically coupled to receive and discharge a hydraulic fluid, and the second
chamber is hydraulically coupled to receive and discharge a drilling fluid. The
separating member is adapted to move within its the pressure vessel in response
to a pressure differential between the first and second chambers. The pump system
also includes a hydraulic control unit adapted to control the plurality of pump units.
