a selected range arc settable spray nozzle with pre - set table precipitation rate in which the arc of coverage adjustment is coupled to an upstream flow throttling valve . as the arc of coverage is adjusted , the opening of the upstream flow throttling valve is proportionally adjusted to maintain the precipitation rate substantially constant independent of arc of coverage adjustments . upstream flow throttling achieved by use of pre - selected number of larger slots for desired flow whose opening area is varied as the arc is being set . the precipitation rate is set by adjusting the throttling valve to provide the desired flow rate for the maximum arc of coverage setting . a pressure compensating valve may also be provided .