An applicator such as a drenching gun for treating livestock is disclosed. The applicator comprises a fluid supply inlet (14), an outlet (4) and a barrel (1) having a barrel outlet (2) and a barrel inlet (15) in fluid communication, or selective fluid communication with the fluid supply inlet (14). A one way outlet valve (3) is in fluid communication with the barrel outlet (2) and with the outlet (4). A piston (5) is disposed in the barrel (1) with piston actuation means for moving the piston relative to the barrel. The applicator further comprises pressure limiting means for limiting a maximum pressure of fluid entering the barrel (1) from the fluid supply inlet (14). The pressure limiting means limits the pressure in the barrel so the outlet valve (3) is not activated unintentionally i.e. by a pressure surge.
