Submersed water pump for river flows. Two cylinders, one with 1 meter diameter and the other 0.2 m/diameter. Pistons are in the same shaft. Area ratio is of 25 X. The bigger cylinder have a shroud of a diameter of 1.5 meter in both ends and is open on both sides. When we submerse it in the river flow the water flows in and pushes the piston. On the other end of the cylinder the water flows out in the direction of the river flow. The piston pushes the second piston, in a closed cylinder ( 0,2m/d) and pressures water. The inlets and outlets of this double side cylinder have retention valves to control aspiration and discharged of the cylinder. The cylinders rotate on its axis, enabling continuous cycles. I need to find the pressure on both cylinders, if the flows at 1 m/s, and power calculations if the pressure water works on micro hydro turbine to produce electric energy.