s used to control the seawater flow (shown in Fig. 3). A sliding
axial spool has various ‘‘land” modulating flow, which moves in a
sleeve containing three ports. When the spool moves, each ‘‘land”
vary the area of the corresponding ports exposed to flow, thus, the
flow versus pressure relationship at the orifices is changed. Assuming
that the spool travel is in general restricted (x 6 l), the simpli-
fied orifice equations derived by linearized analysis [1