Water gun with adjustable pressure chamber

Toy water gun (10) comprising: a housing (12) including a handle (14) with a trigger (16) and a water ejection nozzle (18) disposed therein; a tank water supply (20) connected to the housing (12) fillable water; a water pump (30) located in the housing (12) for pumping water from the supply tank (20) to at least one water pressure chamber (40); including the pressure chamber of water (40) at least one fixed wall (46), a first end wall (48), and a movable wall (44) in contact substantially sealed with at least one fixed wall (46) and is slidable in estrangement from the first end wall (48) when the water is pumped into the water pressure chamber (40) and toward the first end wall (48) when the water is discharged; a pressure chamber air (60); an air pump (62) connected to the air pressure chamber (60) for pressurizing the air pressure chamber (60) with an air pressure desired by the user; and an exhaust valve (70) in fluid communication with the pressure chamber of water (40) so that actuation of the exhaust valve (70) ejects a water jet through the nozzle (18) due, to partially less, the compressed air acting on the movable wall (44), wherein the chamber air pressure is located on one side of the movable wall (44) opposite with respect to the pressure chamber water (40) and it can be pressurized with compressed air to bias the moveable wall (44) toward the first end wall (48).