Multidose delivery pump

1) A delivery pump (1) provided with a plug (20, 21) for the removable coupling to the neck (O) of a container (C) filled with a liquid (L) to be delivered comprising:

• a hollow body (3) defining a suction and compression chamber (4) for said liquid (L) having at least one suction duct (5) for said liquid (L);
• a tight piston (8) sliding in said hollow body (3) to cause inflow and outflow of said liquid (L) into and from said suction and compression chamber (4);
• at least a delivery duct (6) for said liquid (L) communicating with said suction and compression chamber (4);
• valve means (7a, 7b) arranged downstream said suction duct (4) and upstream said delivery duct (6) respectively, adapted to regulate inflow and outflow of said liquid (L) into and from said suction and compression chamber (4);
• elastic means (9) arranged between said tight piston (8) and said hollow body (3);
• first constraint means (10) belonging to said plug (21) cooperating selectively with second constraint means (11) belonging to said tight piston (8) to define the stroke of said piston (8), said stroke being variable according to the mutual position of said first (10) and second (11) constraint means,
• wherein said plug (21) holds a ring nut (13) rotably coupled to said plug, said ring nut being provided with one or more said first constraint means (10) to be coupled to said second constraint means (11).