Ultra high pressure pump

A waterjet cutting apparatus, comprising:

• a cutting head configured to open and close, with pressurized fluid being able to be dispersed from the cutting head when the cutting head is open and the pressurized fluid being prevented from being dispersed from the cutting head when the cutting head is closed;
• a pump arranged to pressurize and supply the pressurized fluid to the cutting head, the pump comprising
• two pistons and two cylinders cooperatively defining two pumping chambers;
• a servo motor comprising a hollow rotor and a stator;
• and
• a drive mechanism comprising a screw arranged co-axial with the hollow rotor, with opposite ends of the screw being coupled to respective ones of the pistons, the drive mechanism being configured to convert alternating rotation of the hollow rotor to reciprocal linear displacement of the screw to pressurize fluid in the pumping chambers;
• a computer-based control system that is operationally connected to the pump, with the control system being configured to control the servo motor, and hence a rate of linear displacement of the screw, such that given geometries of the pumping chambers, pressurized fluid being output by the pump has a fluid pressure greater than 50,000 psi;
• and
• a pressure sensor arranged to measure a fluid pressure that is indicative of a pump output pressure of the pressurized fluid being output by the pump, with a signal from the pressure sensor that indicates the measured fluid pressure being provided to the control system as a pressure feedback signal;
• wherein the computer-based control system is configured to receive and process the pressure feedback signal to control the pump output pressure, without information pertaining to operation of the cutting head, so as to control pressure pulse and dead head spike and, when the cutting head is closed, to store and hold pressure.