Dual-rigid-hollow-stem actuators in opposite-phase slurry pump drive having variable pumping speed and force

A pumping apparatus, comprising:

• means defining first and second variable-volume pumping chambers;
• first and second pumping members reciprocable within the first and second pumping chambers, respectively, to vary the volumes thereof, the pumping chambers each having an inlet for the introduction of material to be pumped and an outlet for the delivery of material from the pumping chamber;
• first and second actuator means coupled to the first and second pumping members, respectively, and operable to reciprocate the pumping members, said first and second actuator means driving said first and second pumping members with mutually opposite phases;
• each of said actuator means comprising
• a cylinder having a cylinder bore therein,
• a plunger located within the cylinder,
• a tubular partition fixed with respect to the cylinder and arranged within the plunger, the partition cooperating with said plunger and said cylinder for defining first and second drive chambers which have different working areas, the plunger being slidable in the cylinder bore and with respect to the tubular partition to vary the volumes of said drive chambers,
• a pump for supplying pressure fluid,
• pump output selection means comprising first and second valve means arranged within conduit means between said pump and said first and second actuator means, respectively, each said valve means being operable to shut off flow of pressure fluid from said pump to one of said drive chambers of its associated actuator means to determine the pumping force transmitted to its associated pumping member,
• and valve control means for controlling operation of said first and second valve means so that both of said first and second valve means are in the same position at any given time and pressure fluid is supplied on alternate strokes to corresponding drive chambers in said first and second actuator means.