Patent ID: 7594541

Claim:
A fluid pump system for a downhole tool connected to a pipe string positioned in a borehole penetrating a subterranean formation, the system comprising: a pump linked to a transmission which is linked to a turbine which is in fluid communication with mud flowing downward through the pipe string, the pump comprising a first pump chamber accommodating a first piston and a second pump chamber accommodating a second piston, wherein: the first and second pistons are connected together and linked to a planetary roller screw which is linked to the transmission which is linked to a motor; and the first and second pump chambers are in fluid communication with a valve block that is in fluid communication with the formation, the borehole and at least one fluid sample chamber; a first pressure sensor disposed between the pump and a first side of a valve; a second pressure sensor disposed on a second side of the valve; and a controller linked to the motor and the first and second pressure sensors, wherein the controller is configured to: control the pump based on at least one parameter selected from the group consisting of mud volumetric flow rate, tool temperature, formation pressure, fluid mobility, system losses, mechanical load limitations, borehole pressure, available power, electrical load limitations and combinations thereof; and open the valve once the pressure obtained by the first sensor is substantially similar to the pressure obtained by the second sensor.