Rotary drive sprinkler

DETAILED DESCRIPTION In accordance with the invention, an improved rotary drive sprinkler includes a spray head rotatably driven in a series of relatively small rotational steps by a water-powered piston drive assembly.
The piston drive assembly indexes the spray head through continuous full-circle rotation or reversibly between selected end limits of a part-circle arcuate path, with the stepping rate and angular magnitude of the steps being substantially constant throughout a broad range of normal water inlet supply pressures.
A stream of irrigation water is projected outwardly from the spray head to irrigate surrounding terrain area.
In accordance with a preferred form of the invention, the improved rotary drive sprinkler comprises a generally hollow spinkler housing having a lower water inlet.
The spray head is carried by a pop-up stem assembly biased normally by a retraction spring to a retracted position within the sprinkler housing but movable to a spraying position with the spray head elevated above the sprinkler housing upon admission of water under pressure to the sprinkler housing interior.
Water supplied to the sprinkler housing flows through the lower water inlet into communication with a pressure reduction assembly which divides the water flow into a first portion substantially at line pressure and a second portion at a reduced reference pressure.
A reduction valve forming part of the pressure reduction assembly maintains the pressure differential between the first and second water flow portions at a substantially constant magnitude irrespective of line pressure.
The first and second water flow portions are supplied to opposite sides of a drive piston forming an integral part of the piston drive assembly.
The pressure differential displaces the drive piston in one direction against a piston biasing spring and in a direction increasing spring forces applied to a relief vale to open the relief valve at the end of a predetermined drive piston stroke.
The opened relief valve unloads the line pressure from the drive piston, thereby permitting return piston displacement through an opposite stroke under the influence of the piston spring together with reclosure of the relief valve