Regulating pressure of a fluid in a wellbore

A high pressure fluid pump system of a fluid injection system includes a large volume displacement system, having a large volume pump, and low volume displacement system, having a low volume pump, a programmable logic control (PLC) computer coupled with each displacement system. The large volume displacement system is configured to incrementally or continuously increase a pressure of a fluid in a downhole to a predetermined pressure setting below a maximum pressure setting, and the low volume displacement system is configured to increase the pressure of the fluid from the predetermined pressure setting to a pressure setting above the predetermined pressure setting and at or below the maximum pressure setting. The functioning of the high pressure fluid pump system can be monitored, controlled and tested by the PLC computer. One or more graphical user interfaces can be coupled to the PLC computer for user input.