From - Yogesh Patel.
In the screw pump the VFD is required only to control the RPM and for which model no. ACS-350 is suitable. 
The model no. ACS -800 is used for controlling the RPM and also the torque which is not required in our case. 
hence we are recommending model no. ACS-350 and are going ahead with the same. Moreover the price differance of the two models is about  Rs. 30,000/- 
Kindly confirm the same as early as possible. 