Abstract: An improved nozzle unit for periodically dispensing a fluid. The nozzle unit includes a fluid dispensing component mounted for confined displacement in a housing having first and second stop surfaces. The fluid dispensing component, when subjected to a displacement force produced by fluid flowing into the housing under pressure, moves from a primary stored position against the first stop surface to impact the second stop surface in a deployed position in which fluid flows through the dispensing component. At least one of the dispensing component and the housing is shaped and dimensioned to cause fluid flowing through the housing under pressure to produce fluid flow forces counteracting the displacement force which moves the dispensing component from the stored position to the deployed position. The fluid flow forces counteracting the impact force minimize material fatigue caused by the impact force and extend the operational life of the nozzle unit.

Abstract: A hydraulically actuated device is employed as part of a pool cleaning system. An improved structure assembly of a hydraulically actuated core within a housing provides ease of manufacture and assembly. Graded control of the application of pressure and the flow of fluid through the system is provided so that the hydraulic device is actuated in a relatively gradual and graded manner to overcome the deleterious effects of abrupt actuation of such devices and the resultant water hammer, pressure surges which are generated in such abruptly operated systems. Improved jet orifices enclosed within the hydraulically actuated cylinder of the device provide for more efficient disturbance of sediments on the interior surfaces of the pool in the immediate vicinities of the hydraulically actuated devices.