High-pressure pre-compression pump

A pump for dispensing a fluid product comprising a piston (1) secured to an actuation rod (2) and which slides in a pump body (3) having a pump chamber (5) defined between an inlet valve (11) and an outlet valve (12), said outlet valve (12) comprising an outlet valve element (39) sliding during actuation in a sealed manner in the pump chamber (5), said pump chamber (5) comprising passage means (40) so that, at the end of actuation of the pump, said outlet valve element (39) co-operates in a non-sealed manner with said passage means (40) in order to open said outlet valve (12) to allow the expulsion of the product contained in the pump chamber, said inlet valve (11) comprising an inlet valve element (10) which slides after closure of the inlet valve (11) in a sleeve (9) of the pump body (3), said sleeve (9) having a reduced diameter with respect to said pump chamber (5) and containing a spring (20) bearing firstly on said inlet valve element (10) and secondly on a bottom of said sleeve (9), said spring (20), in addition expelling the product, also returning the piston (1) into its rest position, wherein said sleeve (9) has an inner diameter of less than 4.2 mm, said spring (20) having a force of at least 20N, so that said pump dispenses said fluid product at a pressure (P) of at least 15 bars.