A system for removing material with a high velocity jet of working fluid comprises an ultra-high pressure pump having an odd numbered plurality of composite fluid cylinders disposed radially outwardly of an axis of rotation of an eccentric crank. Each composite cylinder includes an inner low pressure cylinder and an outer high pressure cylinder coaxially aligned therewith and the longitudinal axes of the composite cylinders are spaced equilaterally around the crankshaft axis of rotation in a common radial plane. A low pressure piston is mounted in each low pressure cylinder for reciprocation between inner and outer ends and each low pressure piston is interconnected with the crankshaft eccentric to reciprocate on sequential pressure and exhaust strokes during each revolution of the crankshaft. Each high pressure cylinder includes a high pressure piston interconnected with a respective low pressure piston and adapted to reciprocate therewith. A high pressure valve system is provided for each cylinder including an inlet check valve for introducing working fluid into the high pressure cylinder upon successive exhaust strokes thereof. The valve system further includes an outlet check valve for each high pressure cylinder for expelling working fluid under ultra-high pressure as the high pressure piston moves on a pressure stroke.