the distribution valve illustrated in fig1 comprises a valve housing consisting of two t - pieces 1 and 2 , tightly joined together for instance by means of screw thread 3 . the axially aligned through - ports 4 and 5 are connected to a main conduit and the lateral outlet ports 6 and 7 to sprinklers or other distribution devices , or to lateral lines provided with such devices . in their position of rest frusto - conically shaped valve members 8 and 9 are pressed into their seats in the t - pieces 1 and 2 , respectively , by a spring 10 , keeping outlet ports 6 and 7 , respectively , closed . for clarity the valve members are drawn at a small distance away from their seats . the interior of each of valve members 8 and 9 is hollow and is cylindrically shaped for the greater part of its length , but the facing ends of the members are provided with inwardly directed collars 11 and 12 , respectively , which co - operate with a tubular sleeve 13 by means of a locking ring 14 and a flange 15 , respectively . tubular sleeve 13 , henceforth referred to as &# 34 ; the plug receiver &# 34 ;, has frusto - conical shaped entrances 17 to facilitate the receiving of a plug element 16 , which will be described in detail below . with valve members 8 and 9 in their position of rest the fluid can pass freely through these valves and plug receiver 13 , but when a plug element 16 is present in the pipeline this will be carried along by a flow , directed in fig1 to the left as indicated by arrow v , and will arrive in plug receiver 13 , intercepting the flow of the medium through it . forced by the pressure of the fluid on plug element 16 , plug receiver 13 now moves to the left in the direction of arrow v , pulling valve 9 with it , and thereby opening outlet port 7 . in its extreme left position the left front side of plug receiver 13 will engage the radial surface of shoulder 4 &# 39 ; near through - port 4 , thereby preventing the escape of fluid from the distribution valve housing along the outside periphery of valve member 9 or the engaging faces of collar 12 and flange 15 . the sealing between the front side of plug receiver 13 and the radial surface of shoulder 4 &# 39 ; can be sufficiently tight if suitable materials are used . it is possible , however , to provide the shoulder 4 &# 39 ; with a sealing ring . as will be explained afterwards in connection with fig2 plug element 16 is temporarily retained in plug receiver 13 . after a given period plug element 16 leaves plug receiver 13 , with the result that valve 9 under the influence of spring 10 returns to its initial position , taking plug receiver 13 along with it . the various parts of the distribution valve then take up the positions again as shown in fig1 . obviously , if the medium flows in the opposite direction and plug element 16 enters the distribution valve via through - port 4 , valve member 8 will be displaced to the right as seen in fig1 and fluid will leave distribution valve through outlet port 6 . fig2 shows an enlarged cross section view of plug element 16 . the plug element comprises a cylindrical jacket 18 , provided with outer screw thread 19 at one end and closed by bottom 20 at the other end . jacket 18 is further provided with several slots 21 , extending over a given length of the jacket and continuing in the bottom 20 . a disc shaped element 22 provided with as many legs 23 as there are slots 21 is fitted against bottom 20 in such manner that each slot 21 accommodates one leg 23 . the front side of disc 22 has a step to take up o - ring 24 , which is locked into place be a frusto - conical nut 25 , screwed on to a bolt 26 , the head 27 of which lies on the inside of bottom 20 and the shaft of which passes through holes in bottom 20 and disc 22 . jacket 18 encases a first fluid - filled chamber 28 , consisting mainly of a liquid filled elastic tubular bag 29 , closed at one end and provided with a collar 30 at the other end . a cover 31 is fitted into collar 30 and is provided with a seat for check valve 32 . the valve 32 is pressed against its seat in the one side of cover 31 by means of elastic washer 33 , lying against the other side of cover 31 . the space at this side of cover 31 is enclosed by a membrane 34 , which via an o - ring 35 is pressed against cover 31 by plug head 36 , the latter being tightly screwed onto thread 19 . the plug head 36 is provided with o - ring 37 . the space enclosed by membrane 34 forms a second chamber . plug element 16 now functions as follows . when entering plug receiver 13 as described above , the protruding parts 23 &# 39 ; of legs 23 , which are made of a slightly elastic material , are pressed inward by receiver 13 and so the legs are pressed against the tubular bag 29 . this pressure forces the liquid inside bag 29 to seep slowly either through the not leakproof closure of check valve 32 or alternatively through a perforation in cover 31 or valve 32 into the second chamber enclosed by membrane 34 , causing a gradual expansion of the latter . in the course of this process , the legs 23 will be bent inwards to such a position that they cannot prevent plug element 16 from leaving plug receiver 13 any longer . consequently , plug element 16 will be pushed through and out of plug receiver 13 by the pressure of the fluid in the upstream section of the conduit and as already explained above this will allow valve member 9 to return to its initial position and close outlet port 7 . as soon as plug element 16 has left plug receiver 13 , the legs 23 will elastically return to their original position and bag 29 and membrane 34 will elastically resume their original shape . because of this the liquid which has been squeezed out of bag 29 will flow back into it via the now open check valve 32 . as the check valve 32 is open now the return of the liquid will be completed in a very short time and plug element 16 will be ready for service again when it arrives at the next distribution valve . the period during which the plug element 16 is held in the plug receiver 13 depends on the time needed for pressing a certain amount of liquid out of the first chamber , comprising tubular bag 29 , and into the second chamber closed by membrane 34 . this time again depends on the pressure difference between tubular bag 29 and the membrane closed second chamber . this pressure difference can be adjusted by means of a piston 60 slidably mounted inside plug head 36 , a sealing ring 61 being present between piston 60 and the inner wall of the head 36 . the piston is connected with a threaded rod 62 running through a threaded bore in the front wall of the head 36 . by moving the piston 60 in the one or the other direction the pressure of the air present in the space between the piston and the membrane can be changed so that the period will have the desired value . the adjusting rod 62 is locked by means of nut 63 . having activated and passed through all the distribution valves in a pipeline , plug element 16 arrives at a flow control device as illustrated in fig3 . this device consists of a cylindrical housing 38 within which there are two fluid control valves 39 and 40 and two vent control valves 41 and 42 . the fluid control valves 39 and 40 , which are of sliding plunger type and provided with sealing rings 43 , serve to cover or uncover supply inlet ports 44 and 45 in casing 38 . the valves 39 and 40 are provided with at least one hole 39 &# 39 ; and 40 &# 39 ;, respectively , so that fluid can pass through to the vent control valves . to ensure the synchronous displacement of the valves 39 and 40 there is provided valve interconnecting means comprising rod 46 . the vent control valves 41 and 42 are connected with each other by means of a tubular sleeve 47 , slidably mounted on a connecting rod 46 . the sealing surfaces of vent control valves 41 and 42 , formed by sealing rings 48 , co - operate with a bore 49 surrounding the sleeve 47 and connected to vent 50 . vent control valves 41 and 42 are interconnected to fluid control valves 39 and 40 by springs 51 and distance tubes 52 , mounted on connecting rod 46 between each pair of fluid control and vent control valves . in the situation illustrated in fig3 and 4 , the fluid supplied by the main supply line 53 enters through the open supply inlet port 45 and flows through the threaded connection 56 into the pipeline 54 in the direction indicated by arrow v . pipeline 54 comprises a number of distribution valves , shown in fig1 and its other terminal end is connected to the opposite threaded connection 55 of casing 38 near supply inlet port 44 . when a plug element 16 , shown in fig2 is carried along with the fluid flowing through pipeline 54 and received by a distribution valve , it will open one of its lateral outlet ports in the manner described before . after a certain period , plug element 16 will leave this distribution valve and move on to the next one in the series . during this displacement any quantity of fluid present in the pipeline downstream of the plug element is carried in front of it and disposed of through the open vent control valve 41 . having passed through all the distribution valves in the pipeline , plug element 16 engages flow control valve 39 and thereby blocks up the passage 39 &# 39 ;. consequently , the full pressure of the fluid is exerted on the combination of plug element 16 and valve 39 and plug element 16 and supply inlet valve 39 will be moved to the right as viewed in fig3 by which movement supply inlet port 44 is opened and supply inlet port 45 closed . having moved somewhat to the right valve 39 will start putting an increasing load on spring 51 , which will transfer this load to exhaust valve 41 , but valve 41 will remain open for the time being due to the opposing pressure of the fluid on the closed exhaust valve 42 . as soon , however , as supply inlet port 45 has been fully closed valve 39 will push distance tube 52 against valve 41 . the greater force of the fluid on the blocked - up valve 39 will now overcome the lesser opposing force of the fluid on the smaller closed valve 42 , with the result that valve 42 is forced off its seat and valve 41 immediately pressed on to its seat by the compressed spring 51 . from now on fluid control valve 39 and vent control valve 42 are open so that the fluid supplied by the main supply line 53 enters through supply inlet port 44 and flows through pipeline 54 in the opposite direction . plug element 16 will again successively pass through the distribution valves in pipeline 54 , this time entering via their through - ports 4 and opening their lateral outlet ports 6 . in the foregoing , reference has already been made to fig4 showing the lay - out of an distribution system in which the various described components are used . as explained in connection with fig3 the fluid is fed by main supply line 53 to the flow control device with supply inlet ports 44 and 45 and the connections 55 and 56 , respectively . with the control device positioned as shown in fig3 the flow in conduit 54 is to the right , as indicated by arrow v . in fig4 of the drawing , five distribution valves are connected with their through - ports 4 and 5 to the conduit 54 . lateral lines 57 and 58 connect the outlet ports 6 and 7 of the distribution valves to distribution devices , e . g ., sprinklers 59 , shown in fig5 - 7 . in the situation represented in fig4 the plug element starting from the flow control device will first arrive at the distribution valve situated on the extreme right and fluid will be supplied to the first lateral line 58 . after a certain period this flow is interrupted and the fluid will then be supplied to lateral line 58 of the next distribution valve , and so on . when the fluid has been supplied to all lateral lines 58 during a given period , plug element 16 will arrive at fluid control valve 39 of the flow control device as shown in fig3 and will act on the valve to cause a reversal in the direction of fluid flow through conduit 54 . fluid will then be supplied to lateral line 57 of the distribution valve immediately to the left of the flow control device , and subsequently to lateral line 57 of the next distribution valve , and so on . the sprinkler illustrated in fig5 comprises an upright stand pipe 101 , a sprinkler head 102 slidably mounted on it , and a nozzle 103 with orifice 104 , screwed in sprinkler head 102 at an inclined angle . stand pipe 101 is provided with an inside collar 105 which co - operates with a flange 106 on sprinkler head 102 . a sealing ring , e . g . a rubber o - ring 107 has been fitted between collar 105 and flange 106 . the lower part of sprinkler head 102 is provided with toothed crowns 108 and 109 , separated by a recess 110 , into which projects a pin 111 as part of a screw 112 , which is tightly fitted in the wall of stand pipe 101 . water fed under pressure to stand pipe 101 will raise sprinkler head 102 until sealing ring 107 is pressed firmly between collar 105 and flange 106 . in this position , pin 111 rests between adjacent teeth in the lower crown 109 , as indicated in fig6 . when the supply is cut off , the pressure drops and sprinkler head 102 will return to its lower end position . during this downward movement , a sloping flank of one of the teeth in the upper crown 108 will hit against pin 111 and cause sprinkler head 102 to turn in the direction indicated by arrow r until pin 111 rests between two adjacent teeth in crown 108 and sprinkler head 102 can not move downward further . when the water supply is re - established sprinkler head 102 will be pushed upward and the sloping flank of the next tooth in the lower crown 109 will hit against pin 111 , forcing the sprinkler head to slightly turn again in the direction of arrow r in fig6 . during the now following sprinkling period pin 111 will rest between the next pair of adjacent teeth in lower crown 109 and nozzle 103 will consequently point in an other direction than before . in this manner , a different sector of the area surrounding stand pipe 101 will be irrigated during each successive sprinkling period . in the embodiment shown in fig7 rows of teeth 113 and 114 are cut in a raised cam around the periphery of sprinkler head 102 and co - operate with two pins 115 and 116 , screwed or otherwise fastened into the wall of stand pipe 101 . in the drawing , full lines show the locations of pins 115 and 116 when sprinkler head 102 is in its higher end position during sprinkling , and dotted lines show the position of the sprinkler head relative to the pins 115 and 116 when the water supply has been cut off and sprinkler head 102 has returned to its lower end position . evidently , the co - operation of teeth rows and pins has the same effect in both embodiments . however , the arrangement shown in fig7 may have certain advantages from a manufacturing point of view . while there have been described what are believed to be the preferred embodiments of the present invention , those skilled in the art will recognize that other and further modifications may be had thereto without departing from the true spirit and scope of the invention , and it is intended to cover all such embodiments which fall within the true scope of the invention .