Positive-displacement type pump system

A positive-displacement type pump system comprising:

• a common pump housing formed with a plurality of cylinders;
• a plurality of pistons slidably received in the respective cylinders and cooperating therewith to form a plurality of pump units;
• a drive shaft extending into the housing for driving the pistons into reciprocating motion within the respective cylinders;
• and
• control means for adjusting delivery volume of the pump units, including at least (i) first throttle valve means disposed in a first suction passage between a working fluid source and a first group of the pump units for operating a first actuator, for adjusting a flow rate of a working fluid from said working fluid source to be supplied to the pump units of the first group, and (ii) second throttle valve means disposed in a second suction passage between said working fluid source and a second group of said pump units for operating a second actuator, for adjusting a flow rate of a working fluid from said working fluid source to be supplied to the pump units of the second group independently of said first throttle means for the first group, and thereby permitting individual adjustment of the pump units of the first and second groups in terms of their respective delivery volumes.