Requirement is to control a hydraulic valve in linear travel (Valve Travel 0 to 15 mm maximum) and control by close loop controller even non discrete positions say 2.5mm, 5.8 mm etc.,) . hydraulic valve operates at high pressures 65 bars and LVDT (positioned on the valve) feedback is fed to controller. purpose of the valve is for accurate flow control.

Eventhough servo valve control gives good accuracy, due to operating media -Diesel fuel (prone to contaminate servo valves), i would like to use stepper motor or torque motor control with 27V and 10A max current consumption. necessary mechanism will be used for coverting rotational to linear travel of valve (worm or gears...)

Could somebody throw some light which one -stepper or Torque motor is better for a longer run and for accurate control. many thanks in advance

why not just use a linear actuator instead of piece mealing one?

Accuracy will depend on what the sensor is measuring and be taken care of by the loop, it has nothing to do with what motor you use. If you are measuring the valve position there is nothing that will make it accurate because of the contamination you mentioned. On the other hand you can be very accurate if it is actually measuring the flow.