1. Hydraulic axial forces acting on a Francis runner

3. Hydraulic axial forces acting on a Francis runner
F1 = Force from ring area
F2 = Reaction force from the absolute velocity at the inlet.
F3 = Force due to the outlet pressure
F4 = Reaction force from the absolute velocity at the outlet.
F5 = Force due to the pressure between the top cover and the impeller hub at the low pressure side of the labyrinth sealing.
F6 = Force due to the pressure between the top cover and the impeller hub at the high pressure side of the labyrinth sealing.
F7 = Force due to the pressure between the lower cover and the impeller ring at the high pressure side of the labyrinth sealing
F8 = Force due to the pressure at the upper labyrinth sealing
F9 = Force due to the pressure at the lower labyrinth sealing

4. Force from ring area, F1

5. Reaction force from the absolute velocity at the inlet, F2

6. Force due to the outlet pressure, F3

7. Reaction force from the absolute velocity at the outlet, F4

8. Force due to the pressure between the top cover and the impeller hub at the low pressure side of the labyrinth sealing, F5.
where:
hp = pressure of the cooling water for the generator  25 meter water colomn
hp will have another pressure if the water is not used for cooling.
k = 0,50 – 0,55
rp = Dp/2
ri = Dr/2

9. Force due to the pressure between the top cover and the impeller hub at the high pressure side of the labyrinth sealing, F6.

10. Force due to the pressure between the lower cover and the impeller ring at the high pressure side of the labyrinth sealing, F7.

11. Force due to the pressure at the upper labyrinth sealing. F8.
where the pressure at the high pressure side of the labyrinth sealing is:

12. Force due to the pressure at the lower labyrinth sealing. F9.
where the pressure the high pressure side of the labyrinth sealing is:
and hs = pressure head at the draft tube inlet