Improvements in an agricultural manual sprayer for preventing leakage of fluids such as insecticides, herbicides or fungicides that comprises tank with a large storage capacity into which a pressure vessel is installed. A manually activated pumping assembly is connected with the inferior section of the pressure vessel and also with the inferior section of the tank. The pumping assembly comprises a reciprocating piston pump for extracting the fluid from the storage tank and pressurizing it within the pressure vessel. The pressurized fluid is applied with a hose and a throttle valve attached to the pressure vessel. The assembly also comprises a double walled piston and barrier against leakage consisting of a ring with interior lips which seal it against the cylinder preventing the exit of fluid, forcing it to remain in the collection chamber until it is emptied with the downward movement of the piston, returning the liquid from the collection chamber to the storage tank through a return hose and internal ducts.
