Self-adjusting valve system for sporting air guns using PCP or pre-compressed air, comprising a trigger having a support part, which defines a housing, comprising at least one air inlet (2,12), at least one outlet, wherein the self-adjusting valve system furthermore comprises: - a first body, as a valve, which blocks, when in a rest position, the air outlet; - a second body, as a piston, which partially encloses the first body; said second body being blocked by the trigger when in a rest position; - a first elastic means, arranged in the housing, between the second body and the support part, - a slot, formed in the first body, and - a pin, which passes through the slot and fits into certain holes formed in the second body, wherein, when in a passive position, the first elastic means pushes the second body towards the outlet, and the second body in turn pushes the first body towards the outlet and blocks said outlet, and the air pressure coming from the inlets (2,12) is projected towards the first body, thus contributing to the blocking of the outlet, and towards the second body, thus moving said second body in an opposite direction of the outlet; said second body being thus blocked against the trigger; and when in the active position, the trigger rotates and releases the second body which, by the effect of the air pressure projected in the second body compresses the first elastic means and moves said second body in an opposite direction to the outlet; the pin is moved by the slot and when reaching the end of the stroke, said pin drags the first body in an opposite direction to the outlet and releases said outlet, letting out the pressure air from the inlets (2,12), and when the first elastic means is decompressed, it drags the second body towards the outlet thus allowing the blocking of the trigger, pushing the first body towards the outlet and blocking the outlet. - a first body, as a valve, which blocks, when in a rest position, the air outlet; - a second body, as a piston, which partially encloses the first body; said second body being blocked by the trigger when in a rest position; - a first elastic means, arranged in the housing, between the second body and the support part, - a slot, formed in the first body, and - a pin, which passes through the slot and fits into certain holes formed in the second body, when in a passive position, the first elastic means pushes the second body towards the outlet, and the second body in turn pushes the first body towards the outlet and blocks said outlet, and the air pressure coming from the inlets (2,12) is projected towards the first body, thus contributing to the blocking of the outlet, and towards the second body, thus moving said second body in an opposite direction of the outlet; said second body being thus blocked against the trigger; and when in the active position, the trigger rotates and releases the second body which, by the effect of the air pressure projected in the second body compresses the first elastic means and moves said second body in an opposite direction to the outlet; the pin is moved by the slot and when reaching the end of the stroke, said pin drags the first body in an opposite direction to the outlet and releases said outlet, letting out the pressure air from the inlets (2,12), and when the first elastic means is decompressed, it drags the second body towards the outlet thus allowing the blocking of the trigger, pushing the first body towards the outlet and blocking the outlet.