A hand-operated piston pump, particularly for directional control of watercrafts, boats or the like, said pump comprising: a drive shaft, which is rotatably mounted in a housing case, a rotor, which is mounted in the housing case and is rotationally integral with the drive shaft, said rotor having a plurality of axial compression chambers formed in the body of said rotor, said axial compression chambers surrounding the drive shaft, a piston being axially slidably housed in each compression chamber and biased by elastic means, with one end projecting out of one end side of the corresponding compression chamber against a cam track consisting of an annular plate inclined with respect to the axis of rotation of said rotor, a fluid reservoir in said housing case, a valve plate located downstream from said rotor and having at least two separate conduits (106, 306) for the passage of pressurized fluid, which alternately communicate with conduits for drawing/discharging said pressurized fluid, the latter conduits being provided in the bottom delimiting walls of said compression chambers facing toward said valve plate, said valve plate being non-rotatably mounted below said housing case and said valve plate communicating with conduits for supplying and returning the pressurized fluid to a consuming unit through an interposed check valve inserted in a corresponding valve body, said valve body having an upper flange, said upper flange having fluid supply and return channels communicating with said fluid passage conduits (106, 306) of said valve plate, characterized in that said valve plate is mounted to float relative to said upper flange, 0-ring seals or the like being interposed between said valve plate and said upper flange, such that said valve plate is separate from said upper flange. a drive shaft, which is rotatably mounted in a housing case, a rotor, which is mounted in the housing case and is rotationally integral with the drive shaft, said rotor having a plurality of axial compression chambers formed in the body of said rotor, said axial compression chambers surrounding the drive shaft, a piston being axially slidably housed in each compression chamber and biased by elastic means, with one end projecting out of one end side of the corresponding compression chamber against a cam track consisting of an annular plate inclined with respect to the axis of rotation of said rotor, a fluid reservoir in said housing case, a valve plate located downstream from said rotor and having at least two separate conduits (106, 306) for the passage of pressurized fluid, which alternately communicate with conduits for drawing/discharging said pressurized fluid, the latter conduits being provided in the bottom delimiting walls of said compression chambers facing toward said valve plate, said valve plate being non-rotatably mounted below said housing case and said valve plate communicating with conduits for supplying and returning the pressurized fluid to a consuming unit through an interposed check valve inserted in a corresponding valve body, said valve body having an upper flange, said upper flange having fluid supply and return channels communicating with said fluid passage conduits (106, 306) of said valve plate, characterized in that said valve plate is mounted to float relative to said upper flange, 0-ring seals or the like being interposed between said valve plate and said upper flange, such that said valve plate is separate from said upper flange.