Precompression pump for spray discharge of a liquid

A precompression pump for spray discharge of a liquid, wherein said pump includes a first inner compression chamber formed within a pump body between a valve for closing an orifice through which liquid is withdrawn from a storage container and a discharge orifice through which the withdrawn liquid is expelled to a spray-discharge head, the volume of said first chamber being variable by reason of the fact that said chamber is limited by a driving piston which is thrust axially by a moving element within said pump body and continuously urged by first resilient means towards a position corresponding to the maximum volume of the first chamber, and a second intermediate chamber between said first chamber and said discharge orifice which is shut-off by a second valve forming the precompression system and mounted within an internal space of said moving element, said second valve being urged by second resilient means to a position of closure of the discharge orifice from which said second valve is withdrawn in spite of the action of the second resilient means when the liquid is pressurized within the second chamber, said moving element being provided with communication ports which are distributed annularly and open laterally towards the second chamber on an elastic sealing sleeve mounted on the periphery of the moving element at the level of said communication ports, the sleeve being mounted between the second chamber and a third chamber, the moving element being applied directly on the driving piston, a third valve placed within the third chamber which is internal to said moving element being urged by third resilient means towards the driving piston to a position in which it closes an orifice of the driving piston which puts the third chamber into communication with the first chamber.