An improved sprinkler has a flow altering device to change water direction and control the direction of a blade wheel. A gear set causes a sprinkler head's repetitive rotation. The sprinkler head includes a set of corresponding upper plate and lower plate to divide an interior chamber of the sprinkler head to two chambers: a control chamber and a gear chamber. A water inlet pipe connects only with the control chamber to provide water to enter the control chamber. The upper plate and the lower plate form a filtering channel interconnecting between the control chamber and the gear chamber. The water from the control chamber can flow into the gear chamber through the filtering channel. The filtering channel filters the large/coarser particle debris in the water and the water flowing into the gear chamber can lubricate and cool the gear set in the gear chamber.