Abstract: The turning point of two-segment linear closure law is commonly determined by using only the rated working condition of a impulse turbine, which neglects the fact that the maximum water hammer (MWH) happens at partial load rejection. This paper analyzes the MWH behaviors at linear valve closure and derives two inferences for the case of general needle-valve closure. First, for each linear closure region, the local MWH always happens at the end time of its line segment if its time duration is no less than that of one phase; second, the MWH pressure in the whole needle-closure region equals the greatest value of all the first-phase water hammers in all working conditions if in any working conditions no negative water hammer occurs at the nozzle until its total shutdown. Using these two inferences, we further derive a critical turning point formula and come to the conclusion that if the three discrimination formulas are true, then the two regional MWHs used as the basis of this derivation are also the MWH pressures in the whole region of needle valve closure.