referring to fig1 a first embodiment of an adjustable arc of coverage spray nozzle according to this invention , generally indicated at 1 , is comprised of a cylindrical housing 3 , a central body insert 23 , an adjustable arc - of - coverage flow control member 15 , an upstream flow throttling valve assembly 36 , and a rotatable and axially movable central adjusting shaft 71 with a valving head 73 at its lower end , and an adjusting slot 74 at its upper end . cylindrical housing 3 is comprised of a generally circular outer wall 5 that defines an internal cavity 7 , an outlet end closure top wall 9 , the latter including a radically spiraled opening 11 that forms an arcuate water discharge orifice or spray slot , and a downwardly depending externally threaded skirt portion 13 that couples the nozzle to a conventional riser tube 30 , by which pressurized water for the sprinkler may be supplied . a filter 90 is positioned within riser tube 30 , and is retained by a shoulder portion 44 that is held between a complementary shoulder 46 on the inside of tube 30 and the bottom end 48 of skirt portion 13 of housing 3 . filter 90 is of generally conventional construction , and includes a plurality of filter openings 92 through which water flows into an inner cavity 95 at its downstream or top end . cavity 95 functions as a valve housing or body for flow throttling valve assembly 36 , as described below . body insert 23 is positioned in central cavity 7 of housing 3 , and is supported therein by circumferentially spaced axial ribs 12 . these can be integrally molded with insert 23 ; alternatively , a separate spacer including ribs 12 may be positioned in cavity 7 around insert 23 . flow adjusting shaft 71 includes a threaded body portion 72 , a valve adjusting member 73 at its lower end , and an adjustment slot 74 , or the like , at the top . the upper end of flow control adjusting shaft body portion 72 is received in an internally threaded central bore 38 in a body portion 40 of the arc - of - coverage flow control member 15 . the portion of adjusting shaft body 72 that extends below flow control member body 40 is threadedly received in an internally threaded central bore 24 in body insert 23 . the fit between adjusting shaft body 72 and central bore 24 is such that shaft 71 is rotationally and axially movable within bore 24 , while the frictional fit between bore 38 and adjusting shaft body 72 is sufficiently tight that deflector body 40 and adjusting shaft 71 normally move together . thus adjusting shaft 71 moves axially within bore 24 as deflector body 40 is manually rotated to adjust the arc of coverage . the deflector body 40 includes a sloped axially spiraled surface 17 which cooperates with the radially spiraled housing slot 11 to provide a sealable variable - arc exit opening 19 that is rotationally adjustable from approximately zero to 360 degrees . the slope of deflector body 40 also determines the exit angle of the water stream through exit opening 19 , and therefore , the range of the nozzle . further details of the construction and operation of the adjustable arcuate orifice spray nozzle is provided in commonly owned u . s . pat . no . 5 , 588 , 594 , the content of which is incorporated herein by reference as if fully set forth . throttling valve member 73 mounted on the lower end of adjusting shaft 71 cooperates with a cavity 95 at the top of filter 90 to form flow throttling valve assembly 36 . throttling valve member 73 may be formed separately or as an integral part of adjusting shaft 71 . likewise , the flow valve housing may also be created as a cylindrical skirt depending from the bottom of spray nozzle housing insert 23 . the interior wall 91 of cavity 95 includes a downstream outlet orifice region defined by a plurality of axial slots or shaped flow openings 80 which communicate with the lower end 98 of housing cavity 7 . the outside circumference of throttling valve member portion 82 can be a 1 : 1 fit with interior wall 91 of the filter cavity 95 . as adjusting shaft 71 moves axially due to rotation of deflector body 40 , throttling valve member 73 moves up or down within cavity 95 . this progressively uncovers ( or covers ) slots 80 , and changes the flow area and thus the flow rate of valve 36 . after the water flows through outlet slots 80 , it then flows axially upward through passages formed between insert 23 supporting ribs 12 , and through cavity 7 to exit orifice 19 . as will be appreciated by those skilled in the art , the precise configuration of outlet slots 80 , which may have an axially varying width , can be selected in coordination with the configurations of deflector body 40 and arcuate slot 11 , and the pitch of tread 72 to produce desired flow rate variations as valve member 73 moves with shaft 71 . according to this invention , these selections are made so that manual adjustment of the arc of coverage ( by rotating deflector body 40 ) produces a proportional change in the flow area of throttling valve 36 . because of this proportional adjustment , the flow through nozzle opening 19 is substantially constant independent of arc adjustment , and the desired substantially constant precipitation rate can be maintained . as will further be appreciated by those skilled in the art in light of the disclosure herein , the axial position of valve member 73 when slot deflector body 40 is adjusted relative to slot 11 for the maximum arc of coverage determines the maximum flow rate , and therefore the precipitation rate . this remains fixed because adjusting shaft 71 rotates with deflector body 40 . however , as another feature of this invention , the threaded fit between adjusting shaft body 72 and threads 24 is designed to allow shaft 71 to be rotated relative to deflector body 40 for adjustment . thus , if deflector body 40 is immobilized at the position corresponding to the maximum arc of coverage , and a tool is engaged in adjusting slot 74 , the axial position of valve member 73 can be adjusted . this can be done during assembly at the factory to provide nozzles of different precipitation rates for the same range of coverage with the same parts . the proportional flow control and the ability to preset a full arc of coverage position for throttling valve 36 is an important improvement over existing designs . the slope of deflector body 40 primarily determines the spray range . thus , a complete sprinkler system having nozzles with one predetermined precipitation rate for different spray ranges can be assembled from common parts except for interchangeable deflector bodies 40 . filter 90 ( even if the upper end serves as the body of throttling valve 36 ) may be a common part with precipitation rate adjusted by pre - positioning adjusting shaft 71 and flow control head 73 . the illustrated construction allows slots 80 each to be larger than the openings 92 in filter 90 . in contrast , a continuous slot surrounding the outer circumference of valve member upper portion 82 would have to be narrower that the filter opening for short range nozzles and would consequently be more likely to be obstructed by dirt . compensation for this by using a filter with smaller openings would only make the filter more prone to obstruction . even though the spray nozzle range can be somewhat reduced by a smaller spray deflector elevation angle , if the flow rate is not also reduced , the precipitation rate would be very high for the reduced area of coverage , and the spray angle would have to be reduced to flat or inverted unless the flow is throttled upstream or the adjustable arc discharge slot is made small , ( i . e . 0 . 010 in .) for some of the shortest ranges desired . reducing the range in half , for example , reduces the flow rate for the same precipitation rate by a factor of four . fig2 illustrates a modified embodiment of the arc settable spray nozzle of this invention . the modified nozzle , generally denoted at 100 is similar to the embodiment previously described except that the upstream throttling valve is formed by valve member 173 and the valve body is formed by a resilient pressure compensating diaphragm 150 which is snap attached to the bottom end of the spray nozzle body 105 at 106 . member 150 includes an axial slot 191 which functions as an outlet orifice . pressure compensating member 150 includes a folded area 155 . the structure deflects in response to increased inlet water pressure , thereby reducing the throttling slot opening . by properly selecting the thickness and rigidity of folded area 155 , the changes in the size of the throttling slot opening can compensate for pressure variations by their axial position and thus help keep the flow more constant at elevated inlet pressures . ribs 160 may be provided to keep the pressure compensating member 150 from being excessively deflected which might totally shut off the flow at very high pressure . although the present invention has been described in relation to particular embodiments thereof , many other variations and modifications and other uses will become apparent to those skilled in the art . the scope of the present invention is therefore not intended to be limited not by the specific disclosure herein .