As such the overall efficiency incorporates mechanical efficiency,
taking into account mechanical losses in shaft seals and
bearings; volumetric efficiency, taking into account leakage and
coolingwater flow; and hydraulic efficiency, defining the amount of
power extracted by the runner from the power available from the
water. Owing to the tight internal tolerances of the casing the
volumetric efficiency can be approximated to hv z 1, with only
small losses due to cooling water flow, so that