An irrigation sprinkler can include an outer case and a riser extendible from the outer case by water pressure. A nozzle can be rotatably mounted at an upper end of the riser. A water inlet can connect the sprinkler to a water source. A turbine may be mounted in the riser for rotation by water entering a lower end of the riser. A gear train reduction can be mounted in the riser. A gear driven coupling mechanism mounted in the riser may couple the gear train reduction and the nozzle. A pressure regulator can be mounted inside the outer case at the water inlet.
