Trigger dispenser for a liquid comprising: - a container having an inner compartment for the containment of the liquid; - a dispenser head attachable to the container, comprising: a) a pressure chamber and a piston operable by the trigger and slidable in said pressure chamber, in a dispensing step in which it operates with pressure in the pressure chamber and in a return step in which it operates with suction in said pressure chamber; b) a mouth delimited by a mouth wall, in fluid communication with the pressure chamber, suitable for the passage of the liquid entering the pressure chamber during the return step and coming out of said pressure chamber during the active step; c) a dispenser duct suitable for being placed in communication with the pressure chamber by means of said mouth, for dispensing the liquid outwards; d) valve dispenser means comprising an engagement wall, said engagement wall being: i) in a pre-dispensing sub-step of the active step, engaged so as to sealingly slide with a first portion of the mouth wall to prevent the communication of the pressure chamber with the dispenser duct, and characterised in that, said engagement wall being: ii) in a dispensing sub-step of the active step, engaged with a second portion (92a") of the mouth wall, provided with passages to allow the communication of the pressure chamber with the dispenser duct. - a container having an inner compartment for the containment of the liquid; - a dispenser head attachable to the container, comprising: a) a pressure chamber and a piston operable by the trigger and slidable in said pressure chamber, in a dispensing step in which it operates with pressure in the pressure chamber and in a return step in which it operates with suction in said pressure chamber; b) a mouth delimited by a mouth wall, in fluid communication with the pressure chamber, suitable for the passage of the liquid entering the pressure chamber during the return step and coming out of said pressure chamber during the active step; c) a dispenser duct suitable for being placed in communication with the pressure chamber by means of said mouth, for dispensing the liquid outwards; d) valve dispenser means comprising an engagement wall, said engagement wall being: i) in a pre-dispensing sub-step of the active step, engaged so as to sealingly slide with a first portion of the mouth wall to prevent the communication of the pressure chamber with the dispenser duct, and characterised in that, said engagement wall being: ii) in a dispensing sub-step of the active step, engaged with a second portion (92a") of the mouth wall, provided with passages to allow the communication of the pressure chamber with the dispenser duct. a) a pressure chamber and a piston operable by the trigger and slidable in said pressure chamber, in a dispensing step in which it operates with pressure in the pressure chamber and in a return step in which it operates with suction in said pressure chamber; b) a mouth delimited by a mouth wall, in fluid communication with the pressure chamber, suitable for the passage of the liquid entering the pressure chamber during the return step and coming out of said pressure chamber during the active step; c) a dispenser duct suitable for being placed in communication with the pressure chamber by means of said mouth, for dispensing the liquid outwards; d) valve dispenser means comprising an engagement wall, said engagement wall being: i) in a pre-dispensing sub-step of the active step, engaged so as to sealingly slide with a first portion of the mouth wall to prevent the communication of the pressure chamber with the dispenser duct, and characterised in that, said engagement wall being: ii) in a dispensing sub-step of the active step, engaged with a second portion (92a") of the mouth wall, provided with passages to allow the communication of the pressure chamber with the dispenser duct. i) in a pre-dispensing sub-step of the active step, engaged so as to sealingly slide with a first portion of the mouth wall to prevent the communication of the pressure chamber with the dispenser duct, and characterised in that, said engagement wall being: ii) in a dispensing sub-step of the active step, engaged with a second portion (92a") of the mouth wall, provided with passages to allow the communication of the pressure chamber with the dispenser duct.