Hand-operated pump with a free floating sleeve piston

A hand operated pump for fluid distribution comprising:

• a) a pump body defming a pump chamber supplied with an inlet valve;
• b) a hollow control rod movable in said pump body between a rest position and a depressed, lower position, said rod biased to said rest position by a return spring within said pump body, said rod comprising an inner lift duct;
• c) a free floating piston assembled in a sliding manner in said pump body and on said rod to define an outlet valve for sealing the inner lift duct in the rest position of the control rod;
• d) the rod comprising a stop surface, said piston cooperating with said stop surface during its upward sliding to provide a sealing at this level;
• e) said piston comprising a sleeve surrounding said control rod, said sleeve having a lower end in cylindrical sealing contact with said control rod in said rest position and an upper end adapted to function on said stop surface of said rod during the slide of the piston towards the top;
• f) said sleeve having an inner diameter greater than the outer diameter of said rod;
• g) the upper end of said sleeve defming an upper circular sealing stop ridge adapted to engage the stop surface of the rod, said outlet valve being defined at least in part by said cylindrical sealing contact which is adapted to be broken by upward sliding of said piston on the rod at such a height that the stop ridge sealingly engages the stop surface before the cylindrical sealing contact of the outlet valve is broken, thus providing a precompression.